一、JDK中ArrayList是如何实现的
1、先看下ArrayList从上而下的层次图：
说明：
从图中可以看出，ArrayList只是最下层的实现类，集合的规则和扩展都是AbstractList、List、Collection等上层的接口所设定的，而ArrayList实现或继承了上层的规则，然后重新或扩展来处理集合中的数据。
2、看看接口：Iterable<E>中都定义了那些规则？
JDK1.8中的源码：
package java.lang; import java.util.Iterator;
import java.util.Objects;
import java.util.Spliterator;
import java.util.Spliterators;
import java.util.function.Consumer;
public interface Iterable<T> {//实现这个接口允许对象成为 "foreach" 语句的目标。
Iterator<T> iterator();
default void forEach(Consumer<? super T> action) {
Objects.requireNonNull(action);
for (T t : this) {
action.accept(t);
}
}
default Spliterator<T> spliterator() {
return Spliterators.spliteratorUnknownSize(iterator(), 0);
}
}
这里说明一下：
（1）Consumer<? super T> action 可以理解为：实现了Consumer接口的实现类对象。
（2）accept(T t) T 是每一次forEach方法处理的数据类型，t是数据
（3）spliterator()：Spliterator（splitable iterator可分割迭代器）接口是Java为了并行遍历数据源中的元素而设计的迭代器。也就是收JDK1.8版本已经支持多核并发处理集合中的数据了，你只需要告诉JDK你要做什么并行任务，关注业务本身，至于如何并行，怎么并行效率最高，就交给JDK自己去思考和优化速度了。
简单举个forEach的例子：
package com.xfwl.test; import java.util.ArrayList;
import java.util.List;
import java.util.function.Consumer;
@SuppressWarnings("unchecked")
public class Test2 {
public static void main(String[] args) {
List alist=new ArrayList();
alist.add("1");
alist.forEach(new T());
}
/**
* Consumer接口测试实现类T
* @param <E>
*/
static class T implements Consumer{
public T(){}
public void accept(Object e) {
System.out.println("当前数据："+e);
}
public Consumer andThen(Consumer after) {
// TODO Auto-generated method stub
return null;
}
}
}
运行结果：
当前数据：1
总结一下：
（1）接口Iterable，定义了遍历集合中的数据的方法：forEach()，这个方法需要一个实现了Consumer接口的参数；
（2）接口Iterable，定义了一个可以实现并发的迭代器，具体如何实现和优化交给jdk自己处理，我们只负责使用集合即可。
3、看看接口：Collection<E>中定义了那些规则？
JDK1.8中的源码：
package java.util;
import java.util.function.Predicate;
import java.util.stream.Stream;
import java.util.stream.StreamSupport; public interface Collection<E> extends Iterable<E> {
int size(); //获取集合元素总数
boolean isEmpty(); //判断集合是否非空
boolean contains(Object o); //判断集合是否包含指定元素
Iterator<E> iterator(); //获取迭代器
Object[] toArray(); //把集合转化成Object类型数组对象
<T> T[] toArray(T[] a); //把集合转化成指定T类型数组对象
boolean add(E e); //添加数据到集合
boolean remove(Object o); //从集合中移除数据
boolean containsAll(Collection<?> c); //集合是否包含另一个集合
boolean addAll(Collection<? extends E> c); //集合添加另外一个集合
boolean removeAll(Collection<?> c); //集合中移除另外一个集合中的内容
default boolean removeIf(Predicate<? super E> filter) {//JDK1.8开始加入的方法，按指定条件移除集合中的信息
Objects.requireNonNull(filter);
boolean removed = false;
final Iterator<E> each = iterator();
while (each.hasNext()) {
if (filter.test(each.next())) {
each.remove();
removed = true;
}
}
return removed;
}
boolean retainAll(Collection<?> c); //移除此 collection 中未包含在指定 collection 中的所有元素
void clear(); //清除集合中的信息
boolean equals(Object o); //比较此 collection 与指定对象是否相等。
int hashCode(); //返回此 collection 的哈希码值。
@Override
default Spliterator<E> spliterator() { //JDK1.8开始新加入的方法，返回当前集合的并发迭代器
return Spliterators.spliterator(this, 0);
}
default Stream<E> stream() { //JDK1.8开始新加入的方法，通过传入并发迭代器，来使用stream过滤集合数据
return StreamSupport.stream(spliterator(), false);//返回的流是顺序的
}
default Stream<E> parallelStream() { //JDK1.8开始新加入的方法，通过传入并发迭代器，来使用stream过滤集合数据
return StreamSupport.stream(spliterator(), true);//返回的流是并行的
}
}
这里说明一下：
（1）JDK8版本中，接口中可以定义方法的实现了，即方法可以定义方法体了。
（2）Collection中定义了一些针对集合数据的添加，删除，判空，是否存在，整块集合的包含+移除等操作，以及JDK1.8开始新增的方法：removeIf()和spliterator()，stream()以及parallelStream()方法。
简单举个stream()的例子：
package com.xfwl.test; import java.util.Arrays;
import java.util.List;
import java.util.function.Consumer;
import java.util.stream.Collectors;
@SuppressWarnings("unchecked")
public class Test2 {
public static void main(String[] args) {
List<Integer> alist=Arrays.asList(1,2,3,4,5,6,7,8,9,10);
alist=alist.stream().filter(s -> (s>5)).collect(Collectors.toList());//lumbda表达式 for(int i:alist){ System.out.println(i); } } }
运行结果：
6
7
8
9
10
继续修改代码，举个removeIf()的例子：
package com.xfwl.test; import java.util.Arrays;
import java.util.List;
import java.util.function.Consumer;
import java.util.stream.Collectors;
@SuppressWarnings("unchecked")
public class Test2 {
public static void main(String[] args) {
List<Integer> alist=Arrays.asList(1,2,3,4,5,6,7,8,9,10);
alist=alist.stream().filter(s -> (s>5)).collect(Collectors.toList());//lumbda表达式
alist.removeIf(s->s==10);
for(int i:alist){
System.out.println(i);
}
}
}
运行结果：
6
7
8
9
4、看看抽象类：AbstractCollection<E>中定义了那些规则？
JDK1.8中的源码
package java.util;
public abstract class AbstractCollection<E> implements Collection<E> {
protected AbstractCollection() {
}
public abstract Iterator<E> iterator(); public abstract int size(); public boolean isEmpty() {
return size() == 0;
}
public boolean contains(Object o) {
Iterator<E> it = iterator();
if (o==null) {
while (it.hasNext())
if (it.next()==null)
return true;
} else {
while (it.hasNext())
if (o.equals(it.next()))
return true;
}
return false;
}
public Object[] toArray() {
// Estimate size of array; be prepared to see more or fewer elements
Object[] r = new Object[size()];
Iterator<E> it = iterator();
for (int i = 0; i < r.length; i++) {
if (! it.hasNext()) // fewer elements than expected
return Arrays.copyOf(r, i);
r[i] = it.next();
}
return it.hasNext() ? finishToArray(r, it) : r;
}
@SuppressWarnings("unchecked")
public <T> T[] toArray(T[] a) {
// Estimate size of array; be prepared to see more or fewer elements
int size = size();
T[] r = a.length >= size ? a :
(T[])java.lang.reflect.Array
.newInstance(a.getClass().getComponentType(), size);
Iterator<E> it = iterator(); for (int i = 0; i < r.length; i++) {
if (! it.hasNext()) { // fewer elements than expected
if (a == r) {
r[i] = null; // null-terminate
} else if (a.length < i) {
return Arrays.copyOf(r, i);
} else {
System.arraycopy(r, 0, a, 0, i);
if (a.length > i) {
a[i] = null;
}
}
return a;
}
r[i] = (T)it.next();
}
// more elements than expected
return it.hasNext() ? finishToArray(r, it) : r;
} private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
@SuppressWarnings("unchecked")
private static <T> T[] finishToArray(T[] r, Iterator<?> it) {
int i = r.length;
while (it.hasNext()) {
int cap = r.length;
if (i == cap) {
int newCap = cap + (cap >> 1) + 1;
// overflow-conscious code
if (newCap - MAX_ARRAY_SIZE > 0)
newCap = hugeCapacity(cap + 1);
r = Arrays.copyOf(r, newCap);
}
r[i++] = (T)it.next();
}
// trim if overallocated
return (i == r.length) ? r : Arrays.copyOf(r, i);
} private static int hugeCapacity(int minCapacity) {
if (minCapacity < 0) // overflow
throw new OutOfMemoryError
("Required array size too large");
return (minCapacity > MAX_ARRAY_SIZE) ?
Integer.MAX_VALUE :
MAX_ARRAY_SIZE;
}
public boolean add(E e) {
throw new UnsupportedOperationException();
}
public boolean remove(Object o) {
Iterator<E> it = iterator();
if (o==null) {
while (it.hasNext()) {
if (it.next()==null) {
it.remove();
return true;
}
}
} else {
while (it.hasNext()) {
if (o.equals(it.next())) {
it.remove();
return true;
}
}
}
return false;
}
public boolean containsAll(Collection<?> c) {
for (Object e : c)
if (!contains(e))
return false;
return true;
}
public boolean addAll(Collection<? extends E> c) {
boolean modified = false;
for (E e : c)
if (add(e))
modified = true;
return modified;
}
public boolean removeAll(Collection<?> c) {
Objects.requireNonNull(c);
boolean modified = false;
Iterator<?> it = iterator();
while (it.hasNext()) {
if (c.contains(it.next())) {
it.remove();
modified = true;
}
}
return modified;
}
public boolean retainAll(Collection<?> c) {
Objects.requireNonNull(c);
boolean modified = false;
Iterator<E> it = iterator();
while (it.hasNext()) {
if (!c.contains(it.next())) {
it.remove();
modified = true;
}
}
return modified;
}
public void clear() {
Iterator<E> it = iterator();
while (it.hasNext()) {
it.next();
it.remove();
}
}
public String toString() {
Iterator<E> it = iterator();
if (! it.hasNext())
return "[]"; StringBuilder sb = new StringBuilder();
sb.append('[');
for (;;) {
E e = it.next();
sb.append(e == this ? "(this Collection)" : e);
if (! it.hasNext())
return sb.append(']').toString();
sb.append(',').append(' ');
}
} }
说明一下：
（1）整体上来看，抽象类：AbstractCollection<E>实现了Collection接口，并且定义了接口中没有实现的方法体。
（2）其中的： public abstract Iterator<E> iterator(); 依然是沿用之前jdk版本的使用方式，当前抽象类没有给出具体的实现，在另外一个抽象类AbstractList中给出了具体实现：
public Iterator<E> iterator() {
return new Itr();
}
那么其中：new Itr()拿到的到底是什么呢？
继续贴出jdk中的源码：
private class Itr implements Iterator<E> {
int cursor = 0; //下一个元素的索引下标
int lastRet = -1; //上一个被调用的元素下标
int expectedModCount = modCount;
public boolean hasNext() {
return cursor != size();
}
public E next() { //返回下一个元素
checkForComodification();
try {
int i = cursor;
E next = get(i);
lastRet = i;
cursor = i + 1;
return next;
} catch (IndexOutOfBoundsException e) {
checkForComodification();
throw new NoSuchElementException();
}
}
public void remove() { //移除元素
if (lastRet < 0)
throw new IllegalStateException();
checkForComodification();
try {
AbstractList.this.remove(lastRet);
if (lastRet < cursor)
cursor--;
lastRet = -1;
expectedModCount = modCount;
} catch (IndexOutOfBoundsException e) {
throw new ConcurrentModificationException();
}
}
final void checkForComodification() {
if (modCount != expectedModCount)
throw new ConcurrentModificationException();
}
}
总结一下：
到目前为止，我们知道，如果只是想简单地获取集合的迭代器（非并行），可直接调用集合的iterator()方法即可，但是如果想要调用几何的并发的迭代器，则需要换一个JDK1.8新增进去的方法：
default Stream<E> stream() { //JDK1.8开始新加入的方法，通过传入并发迭代器，来使用stream过滤集合数据
return StreamSupport.stream(spliterator(), false);//返回的流是顺序的
}
default Stream<E> parallelStream() { //JDK1.8开始新加入的方法，通过传入并发迭代器，来使用stream过滤集合数据
return StreamSupport.stream(spliterator(), true);//返回的流是并行的
}
5、看看抽象类：AbstractList<E>中定义了那些规则？
贴上JDK1.8中的源码：
package java.util;
public abstract class AbstractList<E> extends AbstractCollection<E> implements List<E> { protected AbstractList() {
}
public boolean add(E e) {
add(size(), e);
return true;
} abstract public E get(int index); public E set(int index, E element) {
throw new UnsupportedOperationException();
}
public void add(int index, E element) {
throw new UnsupportedOperationException();
} public E remove(int index) {
throw new UnsupportedOperationException();
}
public int indexOf(Object o) {
ListIterator<E> it = listIterator();
if (o==null) {
while (it.hasNext())
if (it.next()==null)
return it.previousIndex();
} else {
while (it.hasNext())
if (o.equals(it.next()))
return it.previousIndex();
}
return -1;
}
public int lastIndexOf(Object o) {
ListIterator<E> it = listIterator(size());
if (o==null) {
while (it.hasPrevious())
if (it.previous()==null)
return it.nextIndex();
} else {
while (it.hasPrevious())
if (o.equals(it.previous()))
return it.nextIndex();
}
return -1;
} public void clear() {
removeRange(0, size());
}
public boolean addAll(int index, Collection<? extends E> c) {
rangeCheckForAdd(index);
boolean modified = false;
for (E e : c) {
add(index++, e);
modified = true;
}
return modified;
}
public Iterator<E> iterator() {
return new Itr();
}
public ListIterator<E> listIterator() {
return listIterator(0);
}
public ListIterator<E> listIterator(final int index) {
rangeCheckForAdd(index); return new ListItr(index);
} private class Itr implements Iterator<E> { int cursor = 0; int lastRet = -1; int expectedModCount = modCount; public boolean hasNext() {
return cursor != size();
} public E next() {
checkForComodification();
try {
int i = cursor;
E next = get(i);
lastRet = i;
cursor = i + 1;
return next;
} catch (IndexOutOfBoundsException e) {
checkForComodification();
throw new NoSuchElementException();
}
} public void remove() {
if (lastRet < 0)
throw new IllegalStateException();
checkForComodification(); try {
AbstractList.this.remove(lastRet);
if (lastRet < cursor)
cursor--;
lastRet = -1;
expectedModCount = modCount;
} catch (IndexOutOfBoundsException e) {
throw new ConcurrentModificationException();
}
} final void checkForComodification() {
if (modCount != expectedModCount)
throw new ConcurrentModificationException();
}
} private class ListItr extends Itr implements ListIterator<E> {
ListItr(int index) {
cursor = index;
} public boolean hasPrevious() {
return cursor != 0;
} public E previous() {
checkForComodification();
try {
int i = cursor - 1;
E previous = get(i);
lastRet = cursor = i;
return previous;
} catch (IndexOutOfBoundsException e) {
checkForComodification();
throw new NoSuchElementException();
}
} public int nextIndex() {
return cursor;
} public int previousIndex() {
return cursor-1;
} public void set(E e) {
if (lastRet < 0)
throw new IllegalStateException();
checkForComodification(); try {
AbstractList.this.set(lastRet, e);
expectedModCount = modCount;
} catch (IndexOutOfBoundsException ex) {
throw new ConcurrentModificationException();
}
} public void add(E e) {
checkForComodification(); try {
int i = cursor;
AbstractList.this.add(i, e);
lastRet = -1;
cursor = i + 1;
expectedModCount = modCount;
} catch (IndexOutOfBoundsException ex) {
throw new ConcurrentModificationException();
}
}
}
public List<E> subList(int fromIndex, int toIndex) {
return (this instanceof RandomAccess ?
new RandomAccessSubList<>(this, fromIndex, toIndex) :
new SubList<>(this, fromIndex, toIndex));
}
public boolean equals(Object o) {
if (o == this)
return true;
if (!(o instanceof List))
return false; ListIterator<E> e1 = listIterator();
ListIterator<?> e2 = ((List<?>) o).listIterator();
while (e1.hasNext() && e2.hasNext()) {
E o1 = e1.next();
Object o2 = e2.next();
if (!(o1==null ? o2==null : o1.equals(o2)))
return false;
}
return !(e1.hasNext() || e2.hasNext());
}
public int hashCode() {
int hashCode = 1;
for (E e : this)
hashCode = 31*hashCode + (e==null ? 0 : e.hashCode());
return hashCode;
}
protected void removeRange(int fromIndex, int toIndex) {
ListIterator<E> it = listIterator(fromIndex);
for (int i=0, n=toIndex-fromIndex; i<n; i++) {
it.next();
it.remove();
}
}
protected transient int modCount = 0; private void rangeCheckForAdd(int index) {
if (index < 0 || index > size())
throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
} private String outOfBoundsMsg(int index) {
return "Index: "+index+", Size: "+size();
}
} class SubList<E> extends AbstractList<E> {
private final AbstractList<E> l;
private final int offset;
private int size; SubList(AbstractList<E> list, int fromIndex, int toIndex) {
if (fromIndex < 0)
throw new IndexOutOfBoundsException("fromIndex = " + fromIndex);
if (toIndex > list.size())
throw new IndexOutOfBoundsException("toIndex = " + toIndex);
if (fromIndex > toIndex)
throw new IllegalArgumentException("fromIndex(" + fromIndex +
") > toIndex(" + toIndex + ")");
l = list;
offset = fromIndex;
size = toIndex - fromIndex;
this.modCount = l.modCount;
} public E set(int index, E element) {
rangeCheck(index);
checkForComodification();
return l.set(index+offset, element);
} public E get(int index) {
rangeCheck(index);
checkForComodification();
return l.get(index+offset);
} public int size() {
checkForComodification();
return size;
} public void add(int index, E element) {
rangeCheckForAdd(index);
checkForComodification();
l.add(index+offset, element);
this.modCount = l.modCount;
size++;
} public E remove(int index) {
rangeCheck(index);
checkForComodification();
E result = l.remove(index+offset);
this.modCount = l.modCount;
size--;
return result;
} protected void removeRange(int fromIndex, int toIndex) {
checkForComodification();
l.removeRange(fromIndex+offset, toIndex+offset);
this.modCount = l.modCount;
size -= (toIndex-fromIndex);
} public boolean addAll(Collection<? extends E> c) {
return addAll(size, c);
} public boolean addAll(int index, Collection<? extends E> c) {
rangeCheckForAdd(index);
int cSize = c.size();
if (cSize==0)
return false; checkForComodification();
l.addAll(offset+index, c);
this.modCount = l.modCount;
size += cSize;
return true;
} public Iterator<E> iterator() {
return listIterator();
} public ListIterator<E> listIterator(final int index) {
checkForComodification();
rangeCheckForAdd(index); return new ListIterator<E>() {
private final ListIterator<E> i = l.listIterator(index+offset); public boolean hasNext() {
return nextIndex() < size;
} public E next() {
if (hasNext())
return i.next();
else
throw new NoSuchElementException();
} public boolean hasPrevious() {
return previousIndex() >= 0;
} public E previous() {
if (hasPrevious())
return i.previous();
else
throw new NoSuchElementException();
} public int nextIndex() {
return i.nextIndex() - offset;
} public int previousIndex() {
return i.previousIndex() - offset;
} public void remove() {
i.remove();
SubList.this.modCount = l.modCount;
size--;
} public void set(E e) {
i.set(e);
} public void add(E e) {
i.add(e);
SubList.this.modCount = l.modCount;
size++;
}
};
} public List<E> subList(int fromIndex, int toIndex) {
return new SubList<>(this, fromIndex, toIndex);
} private void rangeCheck(int index) {
if (index < 0 || index >= size)
throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
} private void rangeCheckForAdd(int index) {
if (index < 0 || index > size)
throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
} private String outOfBoundsMsg(int index) {
return "Index: "+index+", Size: "+size;
} private void checkForComodification() {
if (this.modCount != l.modCount)
throw new ConcurrentModificationException();
}
} class RandomAccessSubList<E> extends SubList<E> implements RandomAccess {
RandomAccessSubList(AbstractList<E> list, int fromIndex, int toIndex) {
super(list, fromIndex, toIndex);
} public List<E> subList(int fromIndex, int toIndex) {
return new RandomAccessSubList<>(this, fromIndex, toIndex);
}
}
简单看一下抽象类的结构图：
说明一下：
这个抽象类中存在：抽象方法的声明，一些具体方法的实现，也内置了一些内部类：
private class Itr implements Iterator<E> {}
private class ListItr extends Itr implements ListIterator<E> {}
以上2两种迭代器丰富了AbstractList这个抽象类的迭代方式，以后继承这个抽象类的子类也可以重写会直接复用，为子类提供了多样化的功能。
一直在说：以上的接口或者抽象类只是在定义集合的规则，有些人就会有疑惑了，明明这个接口或者抽象类中也有一些实现了功能的方法啊。
其实对于一个集合来说，最重要的是什么？是如何把数据存进去，存在哪里，如何存放，如何取出来，如何存放到一个迭代器中（我们都知道是以链表的形式存放），那么从上面的接口或者抽象类中，我并没有发现：
（1）数据的存放的位置（数组，list集合中维护的是数组）。
（2）数据如何存放在迭代器中的链表。
以上这2中核心实现的代码，并不存在于上述的接口和抽象类中，所以我们接着往下看，继续去寻找答案！！！
6、看看接口：List<E>中定义了那些规则？
贴上JDK1.8中的源码：
package java.util;
import java.util.function.UnaryOperator;
public interface List<E> extends Collection<E> {
// Query Operations /**
* Returns the number of elements in this list. If this list contains
* more than <tt>Integer.MAX_VALUE</tt> elements, returns
* <tt>Integer.MAX_VALUE</tt>.
*
* @return the number of elements in this list
*/
int size(); /**
* Returns <tt>true</tt> if this list contains no elements.
*
* @return <tt>true</tt> if this list contains no elements
*/
boolean isEmpty(); /**
* Returns <tt>true</tt> if this list contains the specified element.
* More formally, returns <tt>true</tt> if and only if this list contains
* at least one element <tt>e</tt> such that
* <tt>(o==null ? e==null : o.equals(e))</tt>.
*
* @param o element whose presence in this list is to be tested
* @return <tt>true</tt> if this list contains the specified element
* @throws ClassCastException if the type of the specified element
* is incompatible with this list
* (<a href="Collection.html#optional-restrictions">optional</a>)
* @throws NullPointerException if the specified element is null and this
* list does not permit null elements
* (<a href="Collection.html#optional-restrictions">optional</a>)
*/
boolean contains(Object o); /**
* Returns an iterator over the elements in this list in proper sequence.
*
* @return an iterator over the elements in this list in proper sequence
*/
Iterator<E> iterator(); /**
* Returns an array containing all of the elements in this list in proper
* sequence (from first to last element).
*
* <p>The returned array will be "safe" in that no references to it are
* maintained by this list. (In other words, this method must
* allocate a new array even if this list is backed by an array).
* The caller is thus free to modify the returned array.
*
* <p>This method acts as bridge between array-based and collection-based
* APIs.
*
* @return an array containing all of the elements in this list in proper
* sequence
* @see Arrays#asList(Object[])
*/
Object[] toArray(); /**
* Returns an array containing all of the elements in this list in
* proper sequence (from first to last element); the runtime type of
* the returned array is that of the specified array. If the list fits
* in the specified array, it is returned therein. Otherwise, a new
* array is allocated with the runtime type of the specified array and
* the size of this list.
*
* <p>If the list fits in the specified array with room to spare (i.e.,
* the array has more elements than the list), the element in the array
* immediately following the end of the list is set to <tt>null</tt>.
* (This is useful in determining the length of the list <i>only</i> if
* the caller knows that the list does not contain any null elements.)
*
* <p>Like the {@link #toArray()} method, this method acts as bridge between
* array-based and collection-based APIs. Further, this method allows
* precise control over the runtime type of the output array, and may,
* under certain circumstances, be used to save allocation costs.
*
* <p>Suppose <tt>x</tt> is a list known to contain only strings.
* The following code can be used to dump the list into a newly
* allocated array of <tt>String</tt>:
*
* <pre>{@code
* String[] y = x.toArray(new String[0]);
* }</pre>
*
* Note that <tt>toArray(new Object[0])</tt> is identical in function to
* <tt>toArray()</tt>.
*
* @param a the array into which the elements of this list are to
* be stored, if it is big enough; otherwise, a new array of the
* same runtime type is allocated for this purpose.
* @return an array containing the elements of this list
* @throws ArrayStoreException if the runtime type of the specified array
* is not a supertype of the runtime type of every element in
* this list
* @throws NullPointerException if the specified array is null
*/
<T> T[] toArray(T[] a); // Modification Operations /**
* Appends the specified element to the end of this list (optional
* operation).
*
* <p>Lists that support this operation may place limitations on what
* elements may be added to this list. In particular, some
* lists will refuse to add null elements, and others will impose
* restrictions on the type of elements that may be added. List
* classes should clearly specify in their documentation any restrictions
* on what elements may be added.
*
* @param e element to be appended to this list
* @return <tt>true</tt> (as specified by {@link Collection#add})
* @throws UnsupportedOperationException if the <tt>add</tt> operation
* is not supported by this list
* @throws ClassCastException if the class of the specified element
* prevents it from being added to this list
* @throws NullPointerException if the specified element is null and this
* list does not permit null elements
* @throws IllegalArgumentException if some property of this element
* prevents it from being added to this list
*/
boolean add(E e); /**
* Removes the first occurrence of the specified element from this list,
* if it is present (optional operation). If this list does not contain
* the element, it is unchanged. More formally, removes the element with
* the lowest index <tt>i</tt> such that
* <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt>
* (if such an element exists). Returns <tt>true</tt> if this list
* contained the specified element (or equivalently, if this list changed
* as a result of the call).
*
* @param o element to be removed from this list, if present
* @return <tt>true</tt> if this list contained the specified element
* @throws ClassCastException if the type of the specified element
* is incompatible with this list
* (<a href="Collection.html#optional-restrictions">optional</a>)
* @throws NullPointerException if the specified element is null and this
* list does not permit null elements
* (<a href="Collection.html#optional-restrictions">optional</a>)
* @throws UnsupportedOperationException if the <tt>remove</tt> operation
* is not supported by this list
*/
boolean remove(Object o); // Bulk Modification Operations /**
* Returns <tt>true</tt> if this list contains all of the elements of the
* specified collection.
*
* @param c collection to be checked for containment in this list
* @return <tt>true</tt> if this list contains all of the elements of the
* specified collection
* @throws ClassCastException if the types of one or more elements
* in the specified collection are incompatible with this
* list
* (<a href="Collection.html#optional-restrictions">optional</a>)
* @throws NullPointerException if the specified collection contains one
* or more null elements and this list does not permit null
* elements
* (<a href="Collection.html#optional-restrictions">optional</a>),
* or if the specified collection is null
* @see #contains(Object)
*/
boolean containsAll(Collection<?> c); /**
* Appends all of the elements in the specified collection to the end of
* this list, in the order that they are returned by the specified
* collection's iterator (optional operation). The behavior of this
* operation is undefined if the specified collection is modified while
* the operation is in progress. (Note that this will occur if the
* specified collection is this list, and it's nonempty.)
*
* @param c collection containing elements to be added to this list
* @return <tt>true</tt> if this list changed as a result of the call
* @throws UnsupportedOperationException if the <tt>addAll</tt> operation
* is not supported by this list
* @throws ClassCastException if the class of an element of the specified
* collection prevents it from being added to this list
* @throws NullPointerException if the specified collection contains one
* or more null elements and this list does not permit null
* elements, or if the specified collection is null
* @throws IllegalArgumentException if some property of an element of the
* specified collection prevents it from being added to this list
* @see #add(Object)
*/
boolean addAll(Collection<? extends E> c); /**
* Inserts all of the elements in the specified collection into this
* list at the specified position (optional operation). Shifts the
* element currently at that position (if any) and any subsequent
* elements to the right (increases their indices). The new elements
* will appear in this list in the order that they are returned by the
* specified collection's iterator. The behavior of this operation is
* undefined if the specified collection is modified while the
* operation is in progress. (Note that this will occur if the specified
* collection is this list, and it's nonempty.)
*
* @param index index at which to insert the first element from the
* specified collection
* @param c collection containing elements to be added to this list
* @return <tt>true</tt> if this list changed as a result of the call
* @throws UnsupportedOperationException if the <tt>addAll</tt> operation
* is not supported by this list
* @throws ClassCastException if the class of an element of the specified
* collection prevents it from being added to this list
* @throws NullPointerException if the specified collection contains one
* or more null elements and this list does not permit null
* elements, or if the specified collection is null
* @throws IllegalArgumentException if some property of an element of the
* specified collection prevents it from being added to this list
* @throws IndexOutOfBoundsException if the index is out of range
* (<tt>index < 0 || index > size()</tt>)
*/
boolean addAll(int index, Collection<? extends E> c); /**
* Removes from this list all of its elements that are contained in the
* specified collection (optional operation).
*
* @param c collection containing elements to be removed from this list
* @return <tt>true</tt> if this list changed as a result of the call
* @throws UnsupportedOperationException if the <tt>removeAll</tt> operation
* is not supported by this list
* @throws ClassCastException if the class of an element of this list
* is incompatible with the specified collection
* (<a href="Collection.html#optional-restrictions">optional</a>)
* @throws NullPointerException if this list contains a null element and the
* specified collection does not permit null elements
* (<a href="Collection.html#optional-restrictions">optional</a>),
* or if the specified collection is null
* @see #remove(Object)
* @see #contains(Object)
*/
boolean removeAll(Collection<?> c); /**
* Retains only the elements in this list that are contained in the
* specified collection (optional operation). In other words, removes
* from this list all of its elements that are not contained in the
* specified collection.
*
* @param c collection containing elements to be retained in this list
* @return <tt>true</tt> if this list changed as a result of the call
* @throws UnsupportedOperationException if the <tt>retainAll</tt> operation
* is not supported by this list
* @throws ClassCastException if the class of an element of this list
* is incompatible with the specified collection
* (<a href="Collection.html#optional-restrictions">optional</a>)
* @throws NullPointerException if this list contains a null element and the
* specified collection does not permit null elements
* (<a href="Collection.html#optional-restrictions">optional</a>),
* or if the specified collection is null
* @see #remove(Object)
* @see #contains(Object)
*/
boolean retainAll(Collection<?> c); /**
* Replaces each element of this list with the result of applying the
* operator to that element. Errors or runtime exceptions thrown by
* the operator are relayed to the caller.
*
* @implSpec
* The default implementation is equivalent to, for this {@code list}:
* <pre>{@code
* final ListIterator<E> li = list.listIterator();
* while (li.hasNext()) {
* li.set(operator.apply(li.next()));
* }
* }</pre>
*
* If the list's list-iterator does not support the {@code set} operation
* then an {@code UnsupportedOperationException} will be thrown when
* replacing the first element.
*
* @param operator the operator to apply to each element
* @throws UnsupportedOperationException if this list is unmodifiable.
* Implementations may throw this exception if an element
* cannot be replaced or if, in general, modification is not
* supported
* @throws NullPointerException if the specified operator is null or
* if the operator result is a null value and this list does
* not permit null elements
* (<a href="Collection.html#optional-restrictions">optional</a>)
* @since 1.8
*/
default void replaceAll(UnaryOperator<E> operator) {
Objects.requireNonNull(operator);
final ListIterator<E> li = this.listIterator();
while (li.hasNext()) {
li.set(operator.apply(li.next()));
}
} /**
* Sorts this list according to the order induced by the specified
* {@link Comparator}.
*
* <p>All elements in this list must be <i>mutually comparable</i> using the
* specified comparator (that is, {@code c.compare(e1, e2)} must not throw
* a {@code ClassCastException} for any elements {@code e1} and {@code e2}
* in the list).
*
* <p>If the specified comparator is {@code null} then all elements in this
* list must implement the {@link Comparable} interface and the elements'
* {@linkplain Comparable natural ordering} should be used.
*
* <p>This list must be modifiable, but need not be resizable.
*
* @implSpec
* The default implementation obtains an array containing all elements in
* this list, sorts the array, and iterates over this list resetting each
* element from the corresponding position in the array. (This avoids the
* n<sup>2</sup> log(n) performance that would result from attempting
* to sort a linked list in place.)
*
* @implNote
* This implementation is a stable, adaptive, iterative mergesort that
* requires far fewer than n lg(n) comparisons when the input array is
* partially sorted, while offering the performance of a traditional
* mergesort when the input array is randomly ordered. If the input array
* is nearly sorted, the implementation requires approximately n
* comparisons. Temporary storage requirements vary from a small constant
* for nearly sorted input arrays to n/2 object references for randomly
* ordered input arrays.
*
* <p>The implementation takes equal advantage of ascending and
* descending order in its input array, and can take advantage of
* ascending and descending order in different parts of the same
* input array. It is well-suited to merging two or more sorted arrays:
* simply concatenate the arrays and sort the resulting array.
*
* <p>The implementation was adapted from Tim Peters's list sort for Python
* (<a href="http://svn.python.org/projects/python/trunk/Objects/listsort.txt">
* TimSort</a>). It uses techniques from Peter McIlroy's "Optimistic
* Sorting and Information Theoretic Complexity", in Proceedings of the
* Fourth Annual ACM-SIAM Symposium on Discrete Algorithms, pp 467-474,
* January 1993.
*
* @param c the {@code Comparator} used to compare list elements.
* A {@code null} value indicates that the elements'
* {@linkplain Comparable natural ordering} should be used
* @throws ClassCastException if the list contains elements that are not
* <i>mutually comparable</i> using the specified comparator
* @throws UnsupportedOperationException if the list's list-iterator does
* not support the {@code set} operation
* @throws IllegalArgumentException
* (<a href="Collection.html#optional-restrictions">optional</a>)
* if the comparator is found to violate the {@link Comparator}
* contract
* @since 1.8
*/
@SuppressWarnings({"unchecked", "rawtypes"})
default void sort(Comparator<? super E> c) {
Object[] a = this.toArray();
Arrays.sort(a, (Comparator) c);
ListIterator<E> i = this.listIterator();
for (Object e : a) {
i.next();
i.set((E) e);
}
} /**
* Removes all of the elements from this list (optional operation).
* The list will be empty after this call returns.
*
* @throws UnsupportedOperationException if the <tt>clear</tt> operation
* is not supported by this list
*/
void clear(); // Comparison and hashing /**
* Compares the specified object with this list for equality. Returns
* <tt>true</tt> if and only if the specified object is also a list, both
* lists have the same size, and all corresponding pairs of elements in
* the two lists are <i>equal</i>. (Two elements <tt>e1</tt> and
* <tt>e2</tt> are <i>equal</i> if <tt>(e1==null ? e2==null :
* e1.equals(e2))</tt>.) In other words, two lists are defined to be
* equal if they contain the same elements in the same order. This
* definition ensures that the equals method works properly across
* different implementations of the <tt>List</tt> interface.
*
* @param o the object to be compared for equality with this list
* @return <tt>true</tt> if the specified object is equal to this list
*/
boolean equals(Object o); /**
* Returns the hash code value for this list. The hash code of a list
* is defined to be the result of the following calculation:
* <pre>{@code
* int hashCode = 1;
* for (E e : list)
* hashCode = 31*hashCode + (e==null ? 0 : e.hashCode());
* }</pre>
* This ensures that <tt>list1.equals(list2)</tt> implies that
* <tt>list1.hashCode()==list2.hashCode()</tt> for any two lists,
* <tt>list1</tt> and <tt>list2</tt>, as required by the general
* contract of {@link Object#hashCode}.
*
* @return the hash code value for this list
* @see Object#equals(Object)
* @see #equals(Object)
*/
int hashCode(); // Positional Access Operations /**
* Returns the element at the specified position in this list.
*
* @param index index of the element to return
* @return the element at the specified position in this list
* @throws IndexOutOfBoundsException if the index is out of range
* (<tt>index < 0 || index >= size()</tt>)
*/
E get(int index); /**
* Replaces the element at the specified position in this list with the
* specified element (optional operation).
*
* @param index index of the element to replace
* @param element element to be stored at the specified position
* @return the element previously at the specified position
* @throws UnsupportedOperationException if the <tt>set</tt> operation
* is not supported by this list
* @throws ClassCastException if the class of the specified element
* prevents it from being added to this list
* @throws NullPointerException if the specified element is null and
* this list does not permit null elements
* @throws IllegalArgumentException if some property of the specified
* element prevents it from being added to this list
* @throws IndexOutOfBoundsException if the index is out of range
* (<tt>index < 0 || index >= size()</tt>)
*/
E set(int index, E element); /**
* Inserts the specified element at the specified position in this list
* (optional operation). Shifts the element currently at that position
* (if any) and any subsequent elements to the right (adds one to their
* indices).
*
* @param index index at which the specified element is to be inserted
* @param element element to be inserted
* @throws UnsupportedOperationException if the <tt>add</tt> operation
* is not supported by this list
* @throws ClassCastException if the class of the specified element
* prevents it from being added to this list
* @throws NullPointerException if the specified element is null and
* this list does not permit null elements
* @throws IllegalArgumentException if some property of the specified
* element prevents it from being added to this list
* @throws IndexOutOfBoundsException if the index is out of range
* (<tt>index < 0 || index > size()</tt>)
*/
void add(int index, E element); /**
* Removes the element at the specified position in this list (optional
* operation). Shifts any subsequent elements to the left (subtracts one
* from their indices). Returns the element that was removed from the
* list.
*
* @param index the index of the element to be removed
* @return the element previously at the specified position
* @throws UnsupportedOperationException if the <tt>remove</tt> operation
* is not supported by this list
* @throws IndexOutOfBoundsException if the index is out of range
* (<tt>index < 0 || index >= size()</tt>)
*/
E remove(int index); // Search Operations /**
* Returns the index of the first occurrence of the specified element
* in this list, or -1 if this list does not contain the element.
* More formally, returns the lowest index <tt>i</tt> such that
* <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt>,
* or -1 if there is no such index.
*
* @param o element to search for
* @return the index of the first occurrence of the specified element in
* this list, or -1 if this list does not contain the element
* @throws ClassCastException if the type of the specified element
* is incompatible with this list
* (<a href="Collection.html#optional-restrictions">optional</a>)
* @throws NullPointerException if the specified element is null and this
* list does not permit null elements
* (<a href="Collection.html#optional-restrictions">optional</a>)
*/
int indexOf(Object o); /**
* Returns the index of the last occurrence of the specified element
* in this list, or -1 if this list does not contain the element.
* More formally, returns the highest index <tt>i</tt> such that
* <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt>,
* or -1 if there is no such index.
*
* @param o element to search for
* @return the index of the last occurrence of the specified element in
* this list, or -1 if this list does not contain the element
* @throws ClassCastException if the type of the specified element
* is incompatible with this list
* (<a href="Collection.html#optional-restrictions">optional</a>)
* @throws NullPointerException if the specified element is null and this
* list does not permit null elements
* (<a href="Collection.html#optional-restrictions">optional</a>)
*/
int lastIndexOf(Object o); // List Iterators /**
* Returns a list iterator over the elements in this list (in proper
* sequence).
*
* @return a list iterator over the elements in this list (in proper
* sequence)
*/
ListIterator<E> listIterator(); /**
* Returns a list iterator over the elements in this list (in proper
* sequence), starting at the specified position in the list.
* The specified index indicates the first element that would be
* returned by an initial call to {@link ListIterator#next next}.
* An initial call to {@link ListIterator#previous previous} would
* return the element with the specified index minus one.
*
* @param index index of the first element to be returned from the
* list iterator (by a call to {@link ListIterator#next next})
* @return a list iterator over the elements in this list (in proper
* sequence), starting at the specified position in the list
* @throws IndexOutOfBoundsException if the index is out of range
* ({@code index < 0 || index > size()})
*/
ListIterator<E> listIterator(int index); // View /**
* Returns a view of the portion of this list between the specified
* <tt>fromIndex</tt>, inclusive, and <tt>toIndex</tt>, exclusive. (If
* <tt>fromIndex</tt> and <tt>toIndex</tt> are equal, the returned list is
* empty.) The returned list is backed by this list, so non-structural
* changes in the returned list are reflected in this list, and vice-versa.
* The returned list supports all of the optional list operations supported
* by this list.<p>
*
* This method eliminates the need for explicit range operations (of
* the sort that commonly exist for arrays). Any operation that expects
* a list can be used as a range operation by passing a subList view
* instead of a whole list. For example, the following idiom
* removes a range of elements from a list:
* <pre>{@code
* list.subList(from, to).clear();
* }</pre>
* Similar idioms may be constructed for <tt>indexOf</tt> and
* <tt>lastIndexOf</tt>, and all of the algorithms in the
* <tt>Collections</tt> class can be applied to a subList.<p>
*
* The semantics of the list returned by this method become undefined if
* the backing list (i.e., this list) is <i>structurally modified</i> in
* any way other than via the returned list. (Structural modifications are
* those that change the size of this list, or otherwise perturb it in such
* a fashion that iterations in progress may yield incorrect results.)
*
* @param fromIndex low endpoint (inclusive) of the subList
* @param toIndex high endpoint (exclusive) of the subList
* @return a view of the specified range within this list
* @throws IndexOutOfBoundsException for an illegal endpoint index value
* (<tt>fromIndex < 0 || toIndex > size ||
* fromIndex > toIndex</tt>)
*/
List<E> subList(int fromIndex, int toIndex); /**
* Creates a {@link Spliterator} over the elements in this list.
*
* <p>The {@code Spliterator} reports {@link Spliterator#SIZED} and
* {@link Spliterator#ORDERED}. Implementations should document the
* reporting of additional characteristic values.
*
* @implSpec
* The default implementation creates a
* <em><a href="Spliterator.html#binding">late-binding</a></em> spliterator
* from the list's {@code Iterator}. The spliterator inherits the
* <em>fail-fast</em> properties of the list's iterator.
*
* @implNote
* The created {@code Spliterator} additionally reports
* {@link Spliterator#SUBSIZED}.
*
* @return a {@code Spliterator} over the elements in this list
* @since 1.8
*/
@Override
default Spliterator<E> spliterator() {
return Spliterators.spliterator(this, Spliterator.ORDERED);
}
}
简单看一下抽象类的结构图：
说明一下：
从源码和抽象类的结构图中，同样可以看到：
（1）List接口中没有说明集合数据是存放在哪里的?只是声明了一些集合操作的方法。、
（2）List接口中没有看到迭代器是如何获取集合数据并存放到链表中的：如下：
ListIterator<E> listIterator();
ListIterator<E> listIterator(int index);
所以想要探明究竟，就只能继续往下看，层层往下，直到ArrayList实现子类。
7、看看实现类：ArrayList<E>是如何实现集合功能的？
贴上JDK1.8中的源码：（内容有点多，会在下面捡重要的说明一下）
/*
* Copyright (c) 1997, 2013, Oracle and/or its affiliates. All rights reserved.
* ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*/ package java.util; import java.util.function.Consumer;
import java.util.function.Predicate;
import java.util.function.UnaryOperator; /**
* Resizable-array implementation of the <tt>List</tt> interface. Implements
* all optional list operations, and permits all elements, including
* <tt>null</tt>. In addition to implementing the <tt>List</tt> interface,
* this class provides methods to manipulate the size of the array that is
* used internally to store the list. (This class is roughly equivalent to
* <tt>Vector</tt>, except that it is unsynchronized.)
*
* <p>The <tt>size</tt>, <tt>isEmpty</tt>, <tt>get</tt>, <tt>set</tt>,
* <tt>iterator</tt>, and <tt>listIterator</tt> operations run in constant
* time. The <tt>add</tt> operation runs in <i>amortized constant time</i>,
* that is, adding n elements requires O(n) time. All of the other operations
* run in linear time (roughly speaking). The constant factor is low compared
* to that for the <tt>LinkedList</tt> implementation.
*
* <p>Each <tt>ArrayList</tt> instance has a <i>capacity</i>. The capacity is
* the size of the array used to store the elements in the list. It is always
* at least as large as the list size. As elements are added to an ArrayList,
* its capacity grows automatically. The details of the growth policy are not
* specified beyond the fact that adding an element has constant amortized
* time cost.
*
* <p>An application can increase the capacity of an <tt>ArrayList</tt> instance
* before adding a large number of elements using the <tt>ensureCapacity</tt>
* operation. This may reduce the amount of incremental reallocation.
*
* <p><strong>Note that this implementation is not synchronized.</strong>
* If multiple threads access an <tt>ArrayList</tt> instance concurrently,
* and at least one of the threads modifies the list structurally, it
* <i>must</i> be synchronized externally. (A structural modification is
* any operation that adds or deletes one or more elements, or explicitly
* resizes the backing array; merely setting the value of an element is not
* a structural modification.) This is typically accomplished by
* synchronizing on some object that naturally encapsulates the list.
*
* If no such object exists, the list should be "wrapped" using the
* {@link Collections#synchronizedList Collections.synchronizedList}
* method. This is best done at creation time, to prevent accidental
* unsynchronized access to the list:<pre>
* List list = Collections.synchronizedList(new ArrayList(...));</pre>
*
* <p><a name="fail-fast">
* The iterators returned by this class's {@link #iterator() iterator} and
* {@link #listIterator(int) listIterator} methods are <em>fail-fast</em>:</a>
* if the list is structurally modified at any time after the iterator is
* created, in any way except through the iterator's own
* {@link ListIterator#remove() remove} or
* {@link ListIterator#add(Object) add} methods, the iterator will throw a
* {@link ConcurrentModificationException}. Thus, in the face of
* concurrent modification, the iterator fails quickly and cleanly, rather
* than risking arbitrary, non-deterministic behavior at an undetermined
* time in the future.
*
* <p>Note that the fail-fast behavior of an iterator cannot be guaranteed
* as it is, generally speaking, impossible to make any hard guarantees in the
* presence of unsynchronized concurrent modification. Fail-fast iterators
* throw {@code ConcurrentModificationException} on a best-effort basis.
* Therefore, it would be wrong to write a program that depended on this
* exception for its correctness: <i>the fail-fast behavior of iterators
* should be used only to detect bugs.</i>
*
* <p>This class is a member of the
* <a href="{@docRoot}/../technotes/guides/collections/index.html">
* Java Collections Framework</a>.
*
* @author Josh Bloch
* @author Neal Gafter
* @see Collection
* @see List
* @see LinkedList
* @see Vector
* @since 1.2
*/ public class ArrayList<E> extends AbstractList<E>
implements List<E>, RandomAccess, Cloneable, java.io.Serializable
{
private static final long serialVersionUID = 8683452581122892189L; /**
* Default initial capacity.
*/
private static final int DEFAULT_CAPACITY = 10; /**
* Shared empty array instance used for empty instances.
*/
private static final Object[] EMPTY_ELEMENTDATA = {}; /**
* Shared empty array instance used for default sized empty instances. We
* distinguish this from EMPTY_ELEMENTDATA to know how much to inflate when
* first element is added.
*/
private static final Object[] DEFAULTCAPACITY_EMPTY_ELEMENTDATA = {}; /**
* The array buffer into which the elements of the ArrayList are stored.
* The capacity of the ArrayList is the length of this array buffer. Any
* empty ArrayList with elementData == DEFAULTCAPACITY_EMPTY_ELEMENTDATA
* will be expanded to DEFAULT_CAPACITY when the first element is added.
*/
transient Object[] elementData; // non-private to simplify nested class access /**
* The size of the ArrayList (the number of elements it contains).
*
* @serial
*/
private int size; /**
* Constructs an empty list with the specified initial capacity.
*
* @param initialCapacity the initial capacity of the list
* @throws IllegalArgumentException if the specified initial capacity
* is negative
*/
public ArrayList(int initialCapacity) {
if (initialCapacity > 0) {
this.elementData = new Object[initialCapacity];
} else if (initialCapacity == 0) {
this.elementData = EMPTY_ELEMENTDATA;
} else {
throw new IllegalArgumentException("Illegal Capacity: "+
initialCapacity);
}
} /**
* Constructs an empty list with an initial capacity of ten.
*/
public ArrayList() {
this.elementData = DEFAULTCAPACITY_EMPTY_ELEMENTDATA;
} /**
* Constructs a list containing the elements of the specified
* collection, in the order they are returned by the collection's
* iterator.
*
* @param c the collection whose elements are to be placed into this list
* @throws NullPointerException if the specified collection is null
*/
public ArrayList(Collection<? extends E> c) {
elementData = c.toArray();
if ((size = elementData.length) != 0) {
// c.toArray might (incorrectly) not return Object[] (see 6260652)
if (elementData.getClass() != Object[].class)
elementData = Arrays.copyOf(elementData, size, Object[].class);
} else {
// replace with empty array.
this.elementData = EMPTY_ELEMENTDATA;
}
} /**
* Trims the capacity of this <tt>ArrayList</tt> instance to be the
* list's current size. An application can use this operation to minimize
* the storage of an <tt>ArrayList</tt> instance.
*/
public void trimToSize() {
modCount++;
if (size < elementData.length) {
elementData = (size == 0)
? EMPTY_ELEMENTDATA
: Arrays.copyOf(elementData, size);
}
} /**
* Increases the capacity of this <tt>ArrayList</tt> instance, if
* necessary, to ensure that it can hold at least the number of elements
* specified by the minimum capacity argument.
*
* @param minCapacity the desired minimum capacity
*/
public void ensureCapacity(int minCapacity) {
int minExpand = (elementData != DEFAULTCAPACITY_EMPTY_ELEMENTDATA)
// any size if not default element table
? 0
// larger than default for default empty table. It's already
// supposed to be at default size.
: DEFAULT_CAPACITY; if (minCapacity > minExpand) {
ensureExplicitCapacity(minCapacity);
}
} private void ensureCapacityInternal(int minCapacity) {
if (elementData == DEFAULTCAPACITY_EMPTY_ELEMENTDATA) {
minCapacity = Math.max(DEFAULT_CAPACITY, minCapacity);
} ensureExplicitCapacity(minCapacity);
} private void ensureExplicitCapacity(int minCapacity) {
modCount++; // overflow-conscious code
if (minCapacity - elementData.length > 0)
grow(minCapacity);
} /**
* The maximum size of array to allocate.
* Some VMs reserve some header words in an array.
* Attempts to allocate larger arrays may result in
* OutOfMemoryError: Requested array size exceeds VM limit
*/
private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8; /**
* Increases the capacity to ensure that it can hold at least the
* number of elements specified by the minimum capacity argument.
*
* @param minCapacity the desired minimum capacity
*/
private void grow(int minCapacity) {
// overflow-conscious code
int oldCapacity = elementData.length;
int newCapacity = oldCapacity + (oldCapacity >> 1);
if (newCapacity - minCapacity < 0)
newCapacity = minCapacity;
if (newCapacity - MAX_ARRAY_SIZE > 0)
newCapacity = hugeCapacity(minCapacity);
// minCapacity is usually close to size, so this is a win:
elementData = Arrays.copyOf(elementData, newCapacity);
} private static int hugeCapacity(int minCapacity) {
if (minCapacity < 0) // overflow
throw new OutOfMemoryError();
return (minCapacity > MAX_ARRAY_SIZE) ?
Integer.MAX_VALUE :
MAX_ARRAY_SIZE;
} /**
* Returns the number of elements in this list.
*
* @return the number of elements in this list
*/
public int size() {
return size;
} /**
* Returns <tt>true</tt> if this list contains no elements.
*
* @return <tt>true</tt> if this list contains no elements
*/
public boolean isEmpty() {
return size == 0;
} /**
* Returns <tt>true</tt> if this list contains the specified element.
* More formally, returns <tt>true</tt> if and only if this list contains
* at least one element <tt>e</tt> such that
* <tt>(o==null ? e==null : o.equals(e))</tt>.
*
* @param o element whose presence in this list is to be tested
* @return <tt>true</tt> if this list contains the specified element
*/
public boolean contains(Object o) {
return indexOf(o) >= 0;
} /**
* Returns the index of the first occurrence of the specified element
* in this list, or -1 if this list does not contain the element.
* More formally, returns the lowest index <tt>i</tt> such that
* <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt>,
* or -1 if there is no such index.
*/
public int indexOf(Object o) {
if (o == null) {
for (int i = 0; i < size; i++)
if (elementData[i]==null)
return i;
} else {
for (int i = 0; i < size; i++)
if (o.equals(elementData[i]))
return i;
}
return -1;
} /**
* Returns the index of the last occurrence of the specified element
* in this list, or -1 if this list does not contain the element.
* More formally, returns the highest index <tt>i</tt> such that
* <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt>,
* or -1 if there is no such index.
*/
public int lastIndexOf(Object o) {
if (o == null) {
for (int i = size-1; i >= 0; i--)
if (elementData[i]==null)
return i;
} else {
for (int i = size-1; i >= 0; i--)
if (o.equals(elementData[i]))
return i;
}
return -1;
} /**
* Returns a shallow copy of this <tt>ArrayList</tt> instance. (The
* elements themselves are not copied.)
*
* @return a clone of this <tt>ArrayList</tt> instance
*/
public Object clone() {
try {
ArrayList<?> v = (ArrayList<?>) super.clone();
v.elementData = Arrays.copyOf(elementData, size);
v.modCount = 0;
return v;
} catch (CloneNotSupportedException e) {
// this shouldn't happen, since we are Cloneable
throw new InternalError(e);
}
} /**
* Returns an array containing all of the elements in this list
* in proper sequence (from first to last element).
*
* <p>The returned array will be "safe" in that no references to it are
* maintained by this list. (In other words, this method must allocate
* a new array). The caller is thus free to modify the returned array.
*
* <p>This method acts as bridge between array-based and collection-based
* APIs.
*
* @return an array containing all of the elements in this list in
* proper sequence
*/
public Object[] toArray() {
return Arrays.copyOf(elementData, size);
} /**
* Returns an array containing all of the elements in this list in proper
* sequence (from first to last element); the runtime type of the returned
* array is that of the specified array. If the list fits in the
* specified array, it is returned therein. Otherwise, a new array is
* allocated with the runtime type of the specified array and the size of
* this list.
*
* <p>If the list fits in the specified array with room to spare
* (i.e., the array has more elements than the list), the element in
* the array immediately following the end of the collection is set to
* <tt>null</tt>. (This is useful in determining the length of the
* list <i>only</i> if the caller knows that the list does not contain
* any null elements.)
*
* @param a the array into which the elements of the list are to
* be stored, if it is big enough; otherwise, a new array of the
* same runtime type is allocated for this purpose.
* @return an array containing the elements of the list
* @throws ArrayStoreException if the runtime type of the specified array
* is not a supertype of the runtime type of every element in
* this list
* @throws NullPointerException if the specified array is null
*/
@SuppressWarnings("unchecked")
public <T> T[] toArray(T[] a) {
if (a.length < size)
// Make a new array of a's runtime type, but my contents:
return (T[]) Arrays.copyOf(elementData, size, a.getClass());
System.arraycopy(elementData, 0, a, 0, size);
if (a.length > size)
a[size] = null;
return a;
} // Positional Access Operations @SuppressWarnings("unchecked")
E elementData(int index) {
return (E) elementData[index];
} /**
* Returns the element at the specified position in this list.
*
* @param index index of the element to return
* @return the element at the specified position in this list
* @throws IndexOutOfBoundsException {@inheritDoc}
*/
public E get(int index) {
rangeCheck(index); return elementData(index);
} /**
* Replaces the element at the specified position in this list with
* the specified element.
*
* @param index index of the element to replace
* @param element element to be stored at the specified position
* @return the element previously at the specified position
* @throws IndexOutOfBoundsException {@inheritDoc}
*/
public E set(int index, E element) {
rangeCheck(index); E oldValue = elementData(index);
elementData[index] = element;
return oldValue;
} /**
* Appends the specified element to the end of this list.
*
* @param e element to be appended to this list
* @return <tt>true</tt> (as specified by {@link Collection#add})
*/
public boolean add(E e) {
ensureCapacityInternal(size + 1); // Increments modCount!!
elementData[size++] = e;
return true;
} /**
* Inserts the specified element at the specified position in this
* list. Shifts the element currently at that position (if any) and
* any subsequent elements to the right (adds one to their indices).
*
* @param index index at which the specified element is to be inserted
* @param element element to be inserted
* @throws IndexOutOfBoundsException {@inheritDoc}
*/
public void add(int index, E element) {
rangeCheckForAdd(index); ensureCapacityInternal(size + 1); // Increments modCount!!
System.arraycopy(elementData, index, elementData, index + 1,
size - index);
elementData[index] = element;
size++;
} /**
* Removes the element at the specified position in this list.
* Shifts any subsequent elements to the left (subtracts one from their
* indices).
*
* @param index the index of the element to be removed
* @return the element that was removed from the list
* @throws IndexOutOfBoundsException {@inheritDoc}
*/
public E remove(int index) {
rangeCheck(index); modCount++;
E oldValue = elementData(index); int numMoved = size - index - 1;
if (numMoved > 0)
System.arraycopy(elementData, index+1, elementData, index,
numMoved);
elementData[--size] = null; // clear to let GC do its work return oldValue;
} /**
* Removes the first occurrence of the specified element from this list,
* if it is present. If the list does not contain the element, it is
* unchanged. More formally, removes the element with the lowest index
* <tt>i</tt> such that
* <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt>
* (if such an element exists). Returns <tt>true</tt> if this list
* contained the specified element (or equivalently, if this list
* changed as a result of the call).
*
* @param o element to be removed from this list, if present
* @return <tt>true</tt> if this list contained the specified element
*/
public boolean remove(Object o) {
if (o == null) {
for (int index = 0; index < size; index++)
if (elementData[index] == null) {
fastRemove(index);
return true;
}
} else {
for (int index = 0; index < size; index++)
if (o.equals(elementData[index])) {
fastRemove(index);
return true;
}
}
return false;
} /*
* Private remove method that skips bounds checking and does not
* return the value removed.
*/
private void fastRemove(int index) {
modCount++;
int numMoved = size - index - 1;
if (numMoved > 0)
System.arraycopy(elementData, index+1, elementData, index,
numMoved);
elementData[--size] = null; // clear to let GC do its work
} /**
* Removes all of the elements from this list. The list will
* be empty after this call returns.
*/
public void clear() {
modCount++; // clear to let GC do its work
for (int i = 0; i < size; i++)
elementData[i] = null; size = 0;
} /**
* Appends all of the elements in the specified collection to the end of
* this list, in the order that they are returned by the
* specified collection's Iterator. The behavior of this operation is
* undefined if the specified collection is modified while the operation
* is in progress. (This implies that the behavior of this call is
* undefined if the specified collection is this list, and this
* list is nonempty.)
*
* @param c collection containing elements to be added to this list
* @return <tt>true</tt> if this list changed as a result of the call
* @throws NullPointerException if the specified collection is null
*/
public boolean addAll(Collection<? extends E> c) {
Object[] a = c.toArray();
int numNew = a.length;
ensureCapacityInternal(size + numNew); // Increments modCount
System.arraycopy(a, 0, elementData, size, numNew);
size += numNew;
return numNew != 0;
} /**
* Inserts all of the elements in the specified collection into this
* list, starting at the specified position. Shifts the element
* currently at that position (if any) and any subsequent elements to
* the right (increases their indices). The new elements will appear
* in the list in the order that they are returned by the
* specified collection's iterator.
*
* @param index index at which to insert the first element from the
* specified collection
* @param c collection containing elements to be added to this list
* @return <tt>true</tt> if this list changed as a result of the call
* @throws IndexOutOfBoundsException {@inheritDoc}
* @throws NullPointerException if the specified collection is null
*/
public boolean addAll(int index, Collection<? extends E> c) {
rangeCheckForAdd(index); Object[] a = c.toArray();
int numNew = a.length;
ensureCapacityInternal(size + numNew); // Increments modCount int numMoved = size - index;
if (numMoved > 0)
System.arraycopy(elementData, index, elementData, index + numNew,
numMoved); System.arraycopy(a, 0, elementData, index, numNew);
size += numNew;
return numNew != 0;
} /**
* Removes from this list all of the elements whose index is between
* {@code fromIndex}, inclusive, and {@code toIndex}, exclusive.
* Shifts any succeeding elements to the left (reduces their index).
* This call shortens the list by {@code (toIndex - fromIndex)} elements.
* (If {@code toIndex==fromIndex}, this operation has no effect.)
*
* @throws IndexOutOfBoundsException if {@code fromIndex} or
* {@code toIndex} is out of range
* ({@code fromIndex < 0 ||
* fromIndex >= size() ||
* toIndex > size() ||
* toIndex < fromIndex})
*/
protected void removeRange(int fromIndex, int toIndex) {
modCount++;
int numMoved = size - toIndex;
System.arraycopy(elementData, toIndex, elementData, fromIndex,
numMoved); // clear to let GC do its work
int newSize = size - (toIndex-fromIndex);
for (int i = newSize; i < size; i++) {
elementData[i] = null;
}
size = newSize;
} /**
* Checks if the given index is in range. If not, throws an appropriate
* runtime exception. This method does *not* check if the index is
* negative: It is always used immediately prior to an array access,
* which throws an ArrayIndexOutOfBoundsException if index is negative.
*/
private void rangeCheck(int index) {
if (index >= size)
throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
} /**
* A version of rangeCheck used by add and addAll.
*/
private void rangeCheckForAdd(int index) {
if (index > size || index < 0)
throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
} /**
* Constructs an IndexOutOfBoundsException detail message.
* Of the many possible refactorings of the error handling code,
* this "outlining" performs best with both server and client VMs.
*/
private String outOfBoundsMsg(int index) {
return "Index: "+index+", Size: "+size;
} /**
* Removes from this list all of its elements that are contained in the
* specified collection.
*
* @param c collection containing elements to be removed from this list
* @return {@code true} if this list changed as a result of the call
* @throws ClassCastException if the class of an element of this list
* is incompatible with the specified collection
* (<a href="Collection.html#optional-restrictions">optional</a>)
* @throws NullPointerException if this list contains a null element and the
* specified collection does not permit null elements
* (<a href="Collection.html#optional-restrictions">optional</a>),
* or if the specified collection is null
* @see Collection#contains(Object)
*/
public boolean removeAll(Collection<?> c) {
Objects.requireNonNull(c);
return batchRemove(c, false);
} /**
* Retains only the elements in this list that are contained in the
* specified collection. In other words, removes from this list all
* of its elements that are not contained in the specified collection.
*
* @param c collection containing elements to be retained in this list
* @return {@code true} if this list changed as a result of the call
* @throws ClassCastException if the class of an element of this list
* is incompatible with the specified collection
* (<a href="Collection.html#optional-restrictions">optional</a>)
* @throws NullPointerException if this list contains a null element and the
* specified collection does not permit null elements
* (<a href="Collection.html#optional-restrictions">optional</a>),
* or if the specified collection is null
* @see Collection#contains(Object)
*/
public boolean retainAll(Collection<?> c) {
Objects.requireNonNull(c);
return batchRemove(c, true);
} private boolean batchRemove(Collection<?> c, boolean complement) {
final Object[] elementData = this.elementData;
int r = 0, w = 0;
boolean modified = false;
try {
for (; r < size; r++)
if (c.contains(elementData[r]) == complement)
elementData[w++] = elementData[r];
} finally {
// Preserve behavioral compatibility with AbstractCollection,
// even if c.contains() throws.
if (r != size) {
System.arraycopy(elementData, r,
elementData, w,
size - r);
w += size - r;
}
if (w != size) {
// clear to let GC do its work
for (int i = w; i < size; i++)
elementData[i] = null;
modCount += size - w;
size = w;
modified = true;
}
}
return modified;
} /**
* Save the state of the <tt>ArrayList</tt> instance to a stream (that
* is, serialize it).
*
* @serialData The length of the array backing the <tt>ArrayList</tt>
* instance is emitted (int), followed by all of its elements
* (each an <tt>Object</tt>) in the proper order.
*/
private void writeObject(java.io.ObjectOutputStream s)
throws java.io.IOException{
// Write out element count, and any hidden stuff
int expectedModCount = modCount;
s.defaultWriteObject(); // Write out size as capacity for behavioural compatibility with clone()
s.writeInt(size); // Write out all elements in the proper order.
for (int i=0; i<size; i++) {
s.writeObject(elementData[i]);
} if (modCount != expectedModCount) {
throw new ConcurrentModificationException();
}
} /**
* Reconstitute the <tt>ArrayList</tt> instance from a stream (that is,
* deserialize it).
*/
private void readObject(java.io.ObjectInputStream s)
throws java.io.IOException, ClassNotFoundException {
elementData = EMPTY_ELEMENTDATA; // Read in size, and any hidden stuff
s.defaultReadObject(); // Read in capacity
s.readInt(); // ignored if (size > 0) {
// be like clone(), allocate array based upon size not capacity
ensureCapacityInternal(size); Object[] a = elementData;
// Read in all elements in the proper order.
for (int i=0; i<size; i++) {
a[i] = s.readObject();
}
}
} /**
* Returns a list iterator over the elements in this list (in proper
* sequence), starting at the specified position in the list.
* The specified index indicates the first element that would be
* returned by an initial call to {@link ListIterator#next next}.
* An initial call to {@link ListIterator#previous previous} would
* return the element with the specified index minus one.
*
* <p>The returned list iterator is <a href="#fail-fast"><i>fail-fast</i></a>.
*
* @throws IndexOutOfBoundsException {@inheritDoc}
*/
public ListIterator<E> listIterator(int index) {
if (index < 0 || index > size)
throw new IndexOutOfBoundsException("Index: "+index);
return new ListItr(index);
} /**
* Returns a list iterator over the elements in this list (in proper
* sequence).
*
* <p>The returned list iterator is <a href="#fail-fast"><i>fail-fast</i></a>.
*
* @see #listIterator(int)
*/
public ListIterator<E> listIterator() {
return new ListItr(0);
} /**
* Returns an iterator over the elements in this list in proper sequence.
*
* <p>The returned iterator is <a href="#fail-fast"><i>fail-fast</i></a>.
*
* @return an iterator over the elements in this list in proper sequence
*/
public Iterator<E> iterator() {
return new Itr();
} /**
* An optimized version of AbstractList.Itr
*/
private class Itr implements Iterator<E> {
int cursor; // index of next element to return
int lastRet = -1; // index of last element returned; -1 if no such
int expectedModCount = modCount; public boolean hasNext() {
return cursor != size;
} @SuppressWarnings("unchecked")
public E next() {
checkForComodification();
int i = cursor;
if (i >= size)
throw new NoSuchElementException();
Object[] elementData = ArrayList.this.elementData;
if (i >= elementData.length)
throw new ConcurrentModificationException();
cursor = i + 1;
return (E) elementData[lastRet = i];
} public void remove() {
if (lastRet < 0)
throw new IllegalStateException();
checkForComodification(); try {
ArrayList.this.remove(lastRet);
cursor = lastRet;
lastRet = -1;
expectedModCount = modCount;
} catch (IndexOutOfBoundsException ex) {
throw new ConcurrentModificationException();
}
} @Override
@SuppressWarnings("unchecked")
public void forEachRemaining(Consumer<? super E> consumer) {
Objects.requireNonNull(consumer);
final int size = ArrayList.this.size;
int i = cursor;
if (i >= size) {
return;
}
final Object[] elementData = ArrayList.this.elementData;
if (i >= elementData.length) {
throw new ConcurrentModificationException();
}
while (i != size && modCount == expectedModCount) {
consumer.accept((E) elementData[i++]);
}
// update once at end of iteration to reduce heap write traffic
cursor = i;
lastRet = i - 1;
checkForComodification();
} final void checkForComodification() {
if (modCount != expectedModCount)
throw new ConcurrentModificationException();
}
} /**
* An optimized version of AbstractList.ListItr
*/
private class ListItr extends Itr implements ListIterator<E> {
ListItr(int index) {
super();
cursor = index;
} public boolean hasPrevious() {
return cursor != 0;
} public int nextIndex() {
return cursor;
} public int previousIndex() {
return cursor - 1;
} @SuppressWarnings("unchecked")
public E previous() {
checkForComodification();
int i = cursor - 1;
if (i < 0)
throw new NoSuchElementException();
Object[] elementData = ArrayList.this.elementData;
if (i >= elementData.length)
throw new ConcurrentModificationException();
cursor = i;
return (E) elementData[lastRet = i];
} public void set(E e) {
if (lastRet < 0)
throw new IllegalStateException();
checkForComodification(); try {
ArrayList.this.set(lastRet, e);
} catch (IndexOutOfBoundsException ex) {
throw new ConcurrentModificationException();
}
} public void add(E e) {
checkForComodification(); try {
int i = cursor;
ArrayList.this.add(i, e);
cursor = i + 1;
lastRet = -1;
expectedModCount = modCount;
} catch (IndexOutOfBoundsException ex) {
throw new ConcurrentModificationException();
}
}
} /**
* Returns a view of the portion of this list between the specified
* {@code fromIndex}, inclusive, and {@code toIndex}, exclusive. (If
* {@code fromIndex} and {@code toIndex} are equal, the returned list is
* empty.) The returned list is backed by this list, so non-structural
* changes in the returned list are reflected in this list, and vice-versa.
* The returned list supports all of the optional list operations.
*
* <p>This method eliminates the need for explicit range operations (of
* the sort that commonly exist for arrays). Any operation that expects
* a list can be used as a range operation by passing a subList view
* instead of a whole list. For example, the following idiom
* removes a range of elements from a list:
* <pre>
* list.subList(from, to).clear();
* </pre>
* Similar idioms may be constructed for {@link #indexOf(Object)} and
* {@link #lastIndexOf(Object)}, and all of the algorithms in the
* {@link Collections} class can be applied to a subList.
*
* <p>The semantics of the list returned by this method become undefined if
* the backing list (i.e., this list) is <i>structurally modified</i> in
* any way other than via the returned list. (Structural modifications are
* those that change the size of this list, or otherwise perturb it in such
* a fashion that iterations in progress may yield incorrect results.)
*
* @throws IndexOutOfBoundsException {@inheritDoc}
* @throws IllegalArgumentException {@inheritDoc}
*/
public List<E> subList(int fromIndex, int toIndex) {
subListRangeCheck(fromIndex, toIndex, size);
return new SubList(this, 0, fromIndex, toIndex);
} static void subListRangeCheck(int fromIndex, int toIndex, int size) {
if (fromIndex < 0)
throw new IndexOutOfBoundsException("fromIndex = " + fromIndex);
if (toIndex > size)
throw new IndexOutOfBoundsException("toIndex = " + toIndex);
if (fromIndex > toIndex)
throw new IllegalArgumentException("fromIndex(" + fromIndex +
") > toIndex(" + toIndex + ")");
} private class SubList extends AbstractList<E> implements RandomAccess {
private final AbstractList<E> parent;
private final int parentOffset;
private final int offset;
int size; SubList(AbstractList<E> parent,
int offset, int fromIndex, int toIndex) {
this.parent = parent;
this.parentOffset = fromIndex;
this.offset = offset + fromIndex;
this.size = toIndex - fromIndex;
this.modCount = ArrayList.this.modCount;
} public E set(int index, E e) {
rangeCheck(index);
checkForComodification();
E oldValue = ArrayList.this.elementData(offset + index);
ArrayList.this.elementData[offset + index] = e;
return oldValue;
} public E get(int index) {
rangeCheck(index);
checkForComodification();
return ArrayList.this.elementData(offset + index);
} public int size() {
checkForComodification();
return this.size;
} public void add(int index, E e) {
rangeCheckForAdd(index);
checkForComodification();
parent.add(parentOffset + index, e);
this.modCount = parent.modCount;
this.size++;
} public E remove(int index) {
rangeCheck(index);
checkForComodification();
E result = parent.remove(parentOffset + index);
this.modCount = parent.modCount;
this.size--;
return result;
} protected void removeRange(int fromIndex, int toIndex) {
checkForComodification();
parent.removeRange(parentOffset + fromIndex,
parentOffset + toIndex);
this.modCount = parent.modCount;
this.size -= toIndex - fromIndex;
} public boolean addAll(Collection<? extends E> c) {
return addAll(this.size, c);
} public boolean addAll(int index, Collection<? extends E> c) {
rangeCheckForAdd(index);
int cSize = c.size();
if (cSize==0)
return false; checkForComodification();
parent.addAll(parentOffset + index, c);
this.modCount = parent.modCount;
this.size += cSize;
return true;
} public Iterator<E> iterator() {
return listIterator();
} public ListIterator<E> listIterator(final int index) {
checkForComodification();
rangeCheckForAdd(index);
final int offset = this.offset; return new ListIterator<E>() {
int cursor = index;
int lastRet = -1;
int expectedModCount = ArrayList.this.modCount; public boolean hasNext() {
return cursor != SubList.this.size;
} @SuppressWarnings("unchecked")
public E next() {
checkForComodification();
int i = cursor;
if (i >= SubList.this.size)
throw new NoSuchElementException();
Object[] elementData = ArrayList.this.elementData;
if (offset + i >= elementData.length)
throw new ConcurrentModificationException();
cursor = i + 1;
return (E) elementData[offset + (lastRet = i)];
} public boolean hasPrevious() {
return cursor != 0;
} @SuppressWarnings("unchecked")
public E previous() {
checkForComodification();
int i = cursor - 1;
if (i < 0)
throw new NoSuchElementException();
Object[] elementData = ArrayList.this.elementData;
if (offset + i >= elementData.length)
throw new ConcurrentModificationException();
cursor = i;
return (E) elementData[offset + (lastRet = i)];
} @SuppressWarnings("unchecked")
public void forEachRemaining(Consumer<? super E> consumer) {
Objects.requireNonNull(consumer);
final int size = SubList.this.size;
int i = cursor;
if (i >= size) {
return;
}
final Object[] elementData = ArrayList.this.elementData;
if (offset + i >= elementData.length) {
throw new ConcurrentModificationException();
}
while (i != size && modCount == expectedModCount) {
consumer.accept((E) elementData[offset + (i++)]);
}
// update once at end of iteration to reduce heap write traffic
lastRet = cursor = i;
checkForComodification();
} public int nextIndex() {
return cursor;
} public int previousIndex() {
return cursor - 1;
} public void remove() {
if (lastRet < 0)
throw new IllegalStateException();
checkForComodification(); try {
SubList.this.remove(lastRet);
cursor = lastRet;
lastRet = -1;
expectedModCount = ArrayList.this.modCount;
} catch (IndexOutOfBoundsException ex) {
throw new ConcurrentModificationException();
}
} public void set(E e) {
if (lastRet < 0)
throw new IllegalStateException();
checkForComodification(); try {
ArrayList.this.set(offset + lastRet, e);
} catch (IndexOutOfBoundsException ex) {
throw new ConcurrentModificationException();
}
} public void add(E e) {
checkForComodification(); try {
int i = cursor;
SubList.this.add(i, e);
cursor = i + 1;
lastRet = -1;
expectedModCount = ArrayList.this.modCount;
} catch (IndexOutOfBoundsException ex) {
throw new ConcurrentModificationException();
}
} final void checkForComodification() {
if (expectedModCount != ArrayList.this.modCount)
throw new ConcurrentModificationException();
}
};
} public List<E> subList(int fromIndex, int toIndex) {
subListRangeCheck(fromIndex, toIndex, size);
return new SubList(this, offset, fromIndex, toIndex);
} private void rangeCheck(int index) {
if (index < 0 || index >= this.size)
throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
} private void rangeCheckForAdd(int index) {
if (index < 0 || index > this.size)
throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
} private String outOfBoundsMsg(int index) {
return "Index: "+index+", Size: "+this.size;
} private void checkForComodification() {
if (ArrayList.this.modCount != this.modCount)
throw new ConcurrentModificationException();
} public Spliterator<E> spliterator() {
checkForComodification();
return new ArrayListSpliterator<E>(ArrayList.this, offset,
offset + this.size, this.modCount);
}
} @Override
public void forEach(Consumer<? super E> action) {
Objects.requireNonNull(action);
final int expectedModCount = modCount;
@SuppressWarnings("unchecked")
final E[] elementData = (E[]) this.elementData;
final int size = this.size;
for (int i=0; modCount == expectedModCount && i < size; i++) {
action.accept(elementData[i]);
}
if (modCount != expectedModCount) {
throw new ConcurrentModificationException();
}
} /**
* Creates a <em><a href="Spliterator.html#binding">late-binding</a></em>
* and <em>fail-fast</em> {@link Spliterator} over the elements in this
* list.
*
* <p>The {@code Spliterator} reports {@link Spliterator#SIZED},
* {@link Spliterator#SUBSIZED}, and {@link Spliterator#ORDERED}.
* Overriding implementations should document the reporting of additional
* characteristic values.
*
* @return a {@code Spliterator} over the elements in this list
* @since 1.8
*/
@Override
public Spliterator<E> spliterator() {
return new ArrayListSpliterator<>(this, 0, -1, 0);
} /** Index-based split-by-two, lazily initialized Spliterator */
static final class ArrayListSpliterator<E> implements Spliterator<E> { /*
* If ArrayLists were immutable, or structurally immutable (no
* adds, removes, etc), we could implement their spliterators
* with Arrays.spliterator. Instead we detect as much
* interference during traversal as practical without
* sacrificing much performance. We rely primarily on
* modCounts. These are not guaranteed to detect concurrency
* violations, and are sometimes overly conservative about
* within-thread interference, but detect enough problems to
* be worthwhile in practice. To carry this out, we (1) lazily
* initialize fence and expectedModCount until the latest
* point that we need to commit to the state we are checking
* against; thus improving precision. (This doesn't apply to
* SubLists, that create spliterators with current non-lazy
* values). (2) We perform only a single
* ConcurrentModificationException check at the end of forEach
* (the most performance-sensitive method). When using forEach
* (as opposed to iterators), we can normally only detect
* interference after actions, not before. Further
* CME-triggering checks apply to all other possible
* violations of assumptions for example null or too-small
* elementData array given its size(), that could only have
* occurred due to interference. This allows the inner loop
* of forEach to run without any further checks, and
* simplifies lambda-resolution. While this does entail a
* number of checks, note that in the common case of
* list.stream().forEach(a), no checks or other computation
* occur anywhere other than inside forEach itself. The other
* less-often-used methods cannot take advantage of most of
* these streamlinings.
*/ private final ArrayList<E> list;
private int index; // current index, modified on advance/split
private int fence; // -1 until used; then one past last index
private int expectedModCount; // initialized when fence set /** Create new spliterator covering the given range */
ArrayListSpliterator(ArrayList<E> list, int origin, int fence,
int expectedModCount) {
this.list = list; // OK if null unless traversed
this.index = origin;
this.fence = fence;
this.expectedModCount = expectedModCount;
} private int getFence() { // initialize fence to size on first use
int hi; // (a specialized variant appears in method forEach)
ArrayList<E> lst;
if ((hi = fence) < 0) {
if ((lst = list) == null)
hi = fence = 0;
else {
expectedModCount = lst.modCount;
hi = fence = lst.size;
}
}
return hi;
} public ArrayListSpliterator<E> trySplit() {
int hi = getFence(), lo = index, mid = (lo + hi) >>> 1;
return (lo >= mid) ? null : // divide range in half unless too small
new ArrayListSpliterator<E>(list, lo, index = mid,
expectedModCount);
} public boolean tryAdvance(Consumer<? super E> action) {
if (action == null)
throw new NullPointerException();
int hi = getFence(), i = index;
if (i < hi) {
index = i + 1;
@SuppressWarnings("unchecked") E e = (E)list.elementData[i];
action.accept(e);
if (list.modCount != expectedModCount)
throw new ConcurrentModificationException();
return true;
}
return false;
} public void forEachRemaining(Consumer<? super E> action) {
int i, hi, mc; // hoist accesses and checks from loop
ArrayList<E> lst; Object[] a;
if (action == null)
throw new NullPointerException();
if ((lst = list) != null && (a = lst.elementData) != null) {
if ((hi = fence) < 0) {
mc = lst.modCount;
hi = lst.size;
}
else
mc = expectedModCount;
if ((i = index) >= 0 && (index = hi) <= a.length) {
for (; i < hi; ++i) {
@SuppressWarnings("unchecked") E e = (E) a[i];
action.accept(e);
}
if (lst.modCount == mc)
return;
}
}
throw new ConcurrentModificationException();
} public long estimateSize() {
return (long) (getFence() - index);
} public int characteristics() {
return Spliterator.ORDERED | Spliterator.SIZED | Spliterator.SUBSIZED;
}
} @Override
public boolean removeIf(Predicate<? super E> filter) {
Objects.requireNonNull(filter);
// figure out which elements are to be removed
// any exception thrown from the filter predicate at this stage
// will leave the collection unmodified
int removeCount = 0;
final BitSet removeSet = new BitSet(size);
final int expectedModCount = modCount;
final int size = this.size;
for (int i=0; modCount == expectedModCount && i < size; i++) {
@SuppressWarnings("unchecked")
final E element = (E) elementData[i];
if (filter.test(element)) {
removeSet.set(i);
removeCount++;
}
}
if (modCount != expectedModCount) {
throw new ConcurrentModificationException();
} // shift surviving elements left over the spaces left by removed elements
final boolean anyToRemove = removeCount > 0;
if (anyToRemove) {
final int newSize = size - removeCount;
for (int i=0, j=0; (i < size) && (j < newSize); i++, j++) {
i = removeSet.nextClearBit(i);
elementData[j] = elementData[i];
}
for (int k=newSize; k < size; k++) {
elementData[k] = null; // Let gc do its work
}
this.size = newSize;
if (modCount != expectedModCount) {
throw new ConcurrentModificationException();
}
modCount++;
} return anyToRemove;
} @Override
@SuppressWarnings("unchecked")
public void replaceAll(UnaryOperator<E> operator) {
Objects.requireNonNull(operator);
final int expectedModCount = modCount;
final int size = this.size;
for (int i=0; modCount == expectedModCount && i < size; i++) {
elementData[i] = operator.apply((E) elementData[i]);
}
if (modCount != expectedModCount) {
throw new ConcurrentModificationException();
}
modCount++;
} @Override
@SuppressWarnings("unchecked")
public void sort(Comparator<? super E> c) {
final int expectedModCount = modCount;
Arrays.sort((E[]) elementData, 0, size, c);
if (modCount != expectedModCount) {
throw new ConcurrentModificationException();
}
modCount++;
}
}
贴上类的结构图：
内容太长，分2次截图。
直接看看里面有些什么吧！
（1）存放集合数据的数组！
private static final Object[] EMPTY_ELEMENTDATA = {};//用于空实例的共享空数组实例。
private static final Object[] DEFAULTCAPACITY_EMPTY_ELEMENTDATA = {};//扩展数组
transient Object[] elementData;//存放数据的原始数组
(2）实例化集合对象
//【1】传入集合大小，初始化集合容量，不够时自动扩展
public ArrayList(int initialCapacity) {
if (initialCapacity > 0) {
this.elementData = new Object[initialCapacity];
} else if (initialCapacity == 0) {
this.elementData = EMPTY_ELEMENTDATA;
} else {
throw new IllegalArgumentException("Illegal Capacity: "+
initialCapacity);
}
}
//【2】直接拿到集合实例，不固定集合大小
public ArrayList() {
this.elementData = DEFAULTCAPACITY_EMPTY_ELEMENTDATA;
}
//【3】用另外一个集合来实例化当前集合
public ArrayList(Collection<? extends E> c) {
elementData = c.toArray();
if ((size = elementData.length) != 0) {
if (elementData.getClass() != Object[].class)
elementData = Arrays.copyOf(elementData, size, Object[].class);
} else {
this.elementData = EMPTY_ELEMENTDATA;
}
}
分析说明一下：
（1）如果采用【1】中方式拿到集合对象，那么当超过设置的初始容量的时候是如何扩容的呢？
看下面这个例子：
public static void main(String[] args) throws Exception {
List list=new ArrayList(2);
System.out.println("扩展前集合容量1："+getCapacity(list));
list.add(1);
list.add(2);
System.out.println("扩展前集合容量2："+getCapacity(list));
list.add(3);
list.add(4);
System.out.println("扩展后集合容量3："+getCapacity(list));
list.add(5);
list.add(6);
System.out.println("扩展后集合容量4："+getCapacity(list));
list.add(7);
list.add(8);
System.out.println("扩展后集合容量5："+getCapacity(list));
list.add(9);
System.out.println("扩展后集合容量6："+getCapacity(list));
list.add(10);
System.out.println("扩展后集合容量7："+getCapacity(list));
for(Object o:list){
System.out.println(o);
}
System.out.println("扩展后集合容量8："+getCapacity(list));
}
//反射拿到当前集合保存数据的数组的容量
static int getCapacity(List<?> l) throws Exception {
Field dataField = ArrayList.class.getDeclaredField("elementData");
dataField.setAccessible(true);
return ((Object[]) dataField.get(l)).length;
}
输出结果：
扩展前集合容量1：2
扩展前集合容量2：2
扩展后集合容量3：4
扩展后集合容量4：6
扩展后集合容量5：9
扩展后集合容量6：9
扩展后集合容量7：13
1
2
3
4
5
6
7
8
9
10
扩展后集合容量8：13
从结果上，可以知道，扩展容量并不是均匀扩展的（每次都递增相同的容量），而是发生着变化的，那么这种变化规则是怎么样的呢？
继续分析一下源码中是怎么定义的：
//将指定的元素追加到列表的末尾
public boolean add(E e) {
ensureCapacityInternal(size + 1); // 增量模式计数!!
elementData[size++] = e;
return true;
}
//确定内部容量的方法
private void ensureCapacityInternal(int minCapacity) {
if (elementData == DEFAULTCAPACITY_EMPTY_ELEMENTDATA) {
minCapacity = Math.max(DEFAULT_CAPACITY, minCapacity);
}
ensureExplicitCapacity(minCapacity);
}
private void ensureExplicitCapacity(int minCapacity) {
modCount++;
//判断当前集合是否超多最大容量，即是否有容量溢出现象
if (minCapacity - elementData.length > 0)
grow(minCapacity);
}
//集合内部维护的是数组扩容
private void grow(int minCapacity) {
int oldCapacity = elementData.length;//拿到当前集合大小
int newCapacity = oldCapacity + (oldCapacity >> 1);//计算集合新的容量大小
if (newCapacity - minCapacity < 0)
newCapacity = minCapacity;
if (newCapacity - MAX_ARRAY_SIZE > 0)
newCapacity = hugeCapacity(minCapacity);
//复制旧集合数据到新的集合中（内部维护的数组扩容-产生新的数组）
elementData = Arrays.copyOf(elementData, newCapacity);
}
那么在详细看以下2行代码是如何计算增加的容量的吧：
int oldCapacity = elementData.length;
int newCapacity = oldCapacity + (oldCapacity >> 1);
简单说明一下：“>>”运算符
>>运算规则：按二进制形式把所有的数字向右移动对应巍峨位数，低位移出（舍弃），高位的空位补符号位，即正数补零，负数补1.
语法格式：
需要移位的数字 >> 移位的次数
例如11 >> 2，则是将数字11右移2位
计算过程：11的二进制形式为：0000 0000 0000 0000 0000 0000 0000 1011，然后把低位的最后两个数字移出，因为该数字是正数，所以在高位补零。则得到的最终结果是0000 0000 0000 0000 0000 0000 0000 0010.转换为十进制是3.数学意义：右移一位相当于除2，右移n位相当于除以2的n次方。
举一个简答的例子：
public static void main(String[] args) throws Exception {
for(int i=0;i<=10;i++){
System.out.println("******当前i="+i+"***********");
System.out.println("递增数值："+((i>>1)));
System.out.println("递增数后值："+(i+(i>>1)));
}
}
运行结果：
******当前i=0***********
递增数值：0
递增数后值：0
******当前i=1***********
递增数值：0
递增数后值：1
******当前i=2***********
递增数值：1
递增数后值：3
******当前i=3***********
递增数值：1
递增数后值：4
******当前i=4***********
递增数值：2
递增数后值：6
******当前i=5***********
递增数值：2
递增数后值：7
******当前i=6***********
递增数值：3
递增数后值：9
******当前i=7***********
递增数值：3
递增数后值：10
******当前i=8***********
递增数值：4
递增数后值：12
******当前i=9***********
递增数值：4
递增数后值：13
******当前i=10***********
递增数值：5
递增数后值：15
分析可以知道：每次递增的数值为：源数值的一半，且向下取整得到的数值。
（3）如何添加数据待集合中
ArrayList实现类中提供了2种方法，供添加数据使用：
public boolean add(E e) {//【1】直接在集合末尾添加一个数据
ensureCapacityInternal(size + 1); // 判断数据是否会溢出
elementData[size++] = e;
return true;
}
public void add(int index, E element) {//【2】添加一个数据到集合的指定位置
rangeCheckForAdd(index);//检查位置是否合法
ensureCapacityInternal(size + 1); // 判断数据是否会溢出
System.arraycopy(elementData, index, elementData, index + 1,//System提供了一个静态方法arraycopy(),我们可以使用它来实现数组之间的复制
size - index);
elementData[index] = element;
size++;
}
方法【1】直接在集合末尾添加一个数据，上面已经给出了分析，这里就不在赘述了，那么来看一下方法【2】是怎么处理的！
（1）在指定位置添加一个数据，这个指定的位置，就需要检查是否合法：
rangeCheckForAdd(index);//检查位置是否合法
private void rangeCheckForAdd(int index) {
if (index > size || index < 0)
throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
}
（2）然后就是判断，如果新增了这个元素，会不会导致整个数组的数据溢出，如果会导致溢出现象，则要扩容数组。
具体的方法上面已经给出分析：这里再放一遍代码
private void grow(int minCapacity) {
// overflow-conscious code
int oldCapacity = elementData.length;
int newCapacity = oldCapacity + (oldCapacity >> 1);
if (newCapacity - minCapacity < 0)
newCapacity = minCapacity;
if (newCapacity - MAX_ARRAY_SIZE > 0)
newCapacity = hugeCapacity(minCapacity);
// minCapacity is usually close to size, so this is a win:
elementData = Arrays.copyOf(elementData, newCapacity);
}
（3）此时，位置索引值合法，数组也不会溢出了，就开始要实现如何插入。
System.arraycopy(elementData, index, elementData, index + 1,
size - index);
上面这句代码：
System提供了一个静态方法arraycopy(),我们可以使用它来实现数组之间的复制。其函数原型是：
public static void (Object src,
int srcPos,
Object dest,
int destPos,
int length)
参数说明：
src:源数组； srcPos:源数组要复制的起始位置；
dest:目的数组； destPos:目的数组放置的起始位置； length:复制的长度。
注意：src and dest都必须是同类型或者可以进行转换类型的数组．
有趣的是这个函数可以实现自己到自己复制，比如：
int[] fun ={0,1,2,3,4,5,6};
System.arraycopy(fun,0,fun,3,3);
则结果为：{0,1,2,0,1,2,6};
实现过程是这样的，先生成一个长度为length的临时数组,将fun数组中srcPos
到srcPos+length-1之间的数据拷贝到临时数组中，再执行System.arraycopy(临时数组,0,fun,3,3).
（4）实现了，指定位置之后（包含指定位置）的数据，向后移动的功能后，开始在指定的位置插入数据了。并且数据长度+1
elementData[index] = element;
size++;
(4)如何从集合中删除一个数据
ArrayList实现类中提供了2种方法，供删除数据使用：
public E remove(int index) {//【1】删除指定位置的数据
rangeCheck(index);//检查位置是否合法
modCount++;
E oldValue = elementData(index);//拿到指定位置的数据
int numMoved = size - index - 1;//判断当前删除的位置是否是最后一位，如果是，则不需要移动数组元素，否则就需要移动
if (numMoved > 0)
System.arraycopy(elementData, index+1, elementData, index,
numMoved);
elementData[--size] = null; //置空该位置的数据
return oldValue;
}
public boolean remove(Object o) {//【2】删除指定的数据
if (o == null) {//当前要删除的数据为null
for (int index = 0; index < size; index++)
if (elementData[index] == null) {//遍历数组容量，拿到要删除数据的位置索引值
fastRemove(index);//调用删除元素的方法
return true;
}
} else {//当前要删除的数据不为null
for (int index = 0; index < size; index++)
if (o.equals(elementData[index])) {//遍历数组容量，拿到要删除数据的位置索引值
fastRemove(index);//调用删除元素的方法
return true;
}
}
return false;
}
private void fastRemove(int index) {//快速删除指定位置的元素
modCount++;
int numMoved = size - index - 1;
if (numMoved > 0)
System.arraycopy(elementData, index+1, elementData, index,
numMoved);
elementData[--size] = null; // clear to let GC do its work
}
private void rangeCheck(int index) {//判断当前位置的索引值是否合法
if (index >= size)//要删除的数据的位置不可超过数组容量，说明：如果过小的话，也会造成异常的发生
throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
}
总结一下;
(1)具体如何删除集合数据，上面代码+说明已经很明显了，这里也不在赘述了。
有意思的是：
private void rangeCheck(int index) {//判断当前位置的索引值是否合法
if (index >= size)//要删除的数据的位置不可超过数组容量，说明：如果过小的话，也会造成异常的发生
throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
}
在删除指定位置的数据的时候，对这个位置索引值做了合法性判断。但是只做了上限判断，下限判断 没有做。
（1）当索引值超过数组上限容量的时候，会抛出：throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
（2）当索引值低于数组下限容量值0的时候，如何处理呢？
public static void main(String[] args) throws Exception {
List alist=Arrays.asList(1,2,3,4,5,6,7,8,9,10);
alist.remove(-1);
}
运行结果：
Exception in thread "main" java.lang.UnsupportedOperationException
at java.util.AbstractList.remove(AbstractList.java:161)
at com.xfwl.test.Test4.main(Test4.java:17)
分析说明：
根据运行结果，发现的确会抛出异常，但是并不是在ArrayList这个实现子类中抛出的，而是在ArrayList继承的AbstractList父类中抛出的，ArrayList重写了父类的方法，虽然其中并没有抛出： java.lang.UnsupportedOperationException
但是查看了源码，就可以知道：父类抽象类：AbstractList的remove(int index)方法中，抛出了异常。
public E remove(int index) {
throw new UnsupportedOperationException();
}
还有一种现象：就是我们删除数据的位置超过数组上限值，也抛出：java.lang.UnsupportedOperationException
public static void main(String[] args) {
List alist=Arrays.asList(1,2,3,4,5,6,7,8,9,10);
alist.remove(100);
}
运行结果：
Exception in thread "main" java.lang.UnsupportedOperationException
at java.util.AbstractList.remove(AbstractList.java:161)
at com.xfwl.test.Test2.main(Test2.java:11)
分析说明：
可以看到，超过上限值，也会抛出父类方法中的异常。
总结一下：
首先ArrayList是子类，AbstractList是父类。
（1）当子类中因为超过上限，而抛出：throw new IndexOutOfBoundsException(outOfBoundsMsg(index)); 但是合格异常并没有被处理，会继续往上抛，就会抛到父类中去。而父类AbstractList的实现接口List和继承AbstractCollection类中都没有：
public E remove(int index)这个方法，换句话说就是， public E remove(int index)这个方法在AbstractList这里就终止了，也就抛出了AbstractList中的这个异常。
（2）当子类中因为地域下限时，由于没有异常捕获或者抛出处理，所以同样会到父类中捕获抛出异常。
（5）集合中是如何把数据传递给迭代器中的链表的呢？
分析JDK1.8的源码，可以知道：ArrayList中提供了，三个获取迭代器的方法，2个内置的具有继承关系的迭代器类。
三个获取迭代器的方法：
public ListIterator<E> listIterator(int index) {//【1】获取数组指定位置（不是索引值）之后的数组数据存放入迭代器链表中
if (index < 0 || index > size)
throw new IndexOutOfBoundsException("Index: "+index);
return new ListItr(index);
}
public ListIterator<E> listIterator() {//【2】默认的方法。获取所有的数组数据放入迭代器链表中
return new ListItr(0);
}
public Iterator<E> iterator() {//【3】默认方法。获取所有的数组数据放入迭代器链表中
return new Itr();
}
//说明：【2】和【3】的区别是返回的类型不懂，Iterator是ListIterator的父类
2个内置的迭代器类：
private class Itr implements Iterator<E> {}
Itr类内部结构图：
private class Itr implements Iterator<E> {
int cursor; // index of next element to return
int lastRet = -1; // index of last element returned; -1 if no such
int expectedModCount = modCount;
public boolean hasNext() {
return cursor != size;
}
@SuppressWarnings("unchecked")
public E next() {
checkForComodification();
int i = cursor;
if (i >= size)
throw new NoSuchElementException();
Object[] elementData = ArrayList.this.elementData;
if (i >= elementData.length)
throw new ConcurrentModificationException();
cursor = i + 1;
return (E) elementData[lastRet = i];
}
public void remove() {
if (lastRet < 0)
throw new IllegalStateException();
checkForComodification();
try {
ArrayList.this.remove(lastRet);
cursor = lastRet;
lastRet = -1;
expectedModCount = modCount;
} catch (IndexOutOfBoundsException ex) {
throw new ConcurrentModificationException();
}
}
@Override
@SuppressWarnings("unchecked")
public void forEachRemaining(Consumer<? super E> consumer) {
Objects.requireNonNull(consumer);
final int size = ArrayList.this.size;
int i = cursor;
if (i >= size) {
return;
}
final Object[] elementData = ArrayList.this.elementData;
if (i >= elementData.length) {
throw new ConcurrentModificationException();
}
while (i != size && modCount == expectedModCount) {
consumer.accept((E) elementData[i++]);
}
// update once at end of iteration to reduce heap write traffic
cursor = i;
lastRet = i - 1;
checkForComodification();
}
final void checkForComodification() {
if (modCount != expectedModCount)
throw new ConcurrentModificationException();
}
}
private class ListItr extends Itr implements ListIterator<E> {}
ListItr类内部结构图：
private class ListItr extends Itr implements ListIterator<E> {
ListItr(int index) {
super();
cursor = index;
}
public boolean hasPrevious() {
return cursor != 0;
}
public int nextIndex() {
return cursor;
}
public int previousIndex() {
return cursor - 1;
}
@SuppressWarnings("unchecked")
public E previous() {
checkForComodification();
int i = cursor - 1;
if (i < 0)
throw new NoSuchElementException();
Object[] elementData = ArrayList.this.elementData;
if (i >= elementData.length)
throw new ConcurrentModificationException();
cursor = i;
return (E) elementData[lastRet = i];
}
public void set(E e) {
if (lastRet < 0)
throw new IllegalStateException();
checkForComodification();
try {
ArrayList.this.set(lastRet, e);
} catch (IndexOutOfBoundsException ex) {
throw new ConcurrentModificationException();
}
}
public void add(E e) {
checkForComodification();
try {
int i = cursor;
ArrayList.this.add(i, e);
cursor = i + 1;
lastRet = -1;
expectedModCount = modCount;
} catch (IndexOutOfBoundsException ex) {
throw new ConcurrentModificationException();
}
}
}
从代码中，我们可以看到，这两种迭代器，从根本上来说都是使用实现了 Iterator接口来存储数据，定位数据，移动数据。
关于链表的数据结构，以后会在算法章节做另做模拟、测试和分析。
好了，此篇到此结束了！