public class ArrayList<E> extends AbstractList<E>
implements List<E>, RandomAccess, Cloneable, java.io.Serializable
/** * 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存储方式为Object数组，默认容量为10
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public boolean add(E e) {
ensureCapacityInternal(size + 1); // Increments modCount!!
elementData[size++] = e;
return true;
}ensureCapacityInternal()
private void ensureCapacityInternal(int minCapacity) {
if (elementData == DEFAULTCAPACITY_EMPTY_ELEMENTDATA) {
minCapacity = Math.max(DEFAULT_CAPACITY, minCapacity);
}
ensureExplicitCapacity(minCapacity);
}ensureExplicitCapacity()
private void ensureExplicitCapacity(int minCapacity) {
modCount++;
// overflow-conscious code
if (minCapacity - elementData.length > 0)
grow(minCapacity);
}当添加容量大于当前容器容量时调用grow()扩容
private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
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); }1.扩容容量 = 原容量 + 原容量 / 2
2.如果扩容后容量依旧不足则直接使用添加后的容量大小
3.如果扩容后容量大于MAX_ARRAY_SIZE 即 Integer.MAX_VALUE-8 则调用hugeCapacity方法
4.重新生成一个新容量的容器
private static int hugeCapacity(int minCapacity) {
if (minCapacity < 0) // overflow
throw new OutOfMemoryError();
return (minCapacity > MAX_ARRAY_SIZE) ?
Integer.MAX_VALUE :
MAX_ARRAY_SIZE;
}接上一步3， 在不溢出的情况下，最大容量为Integer.MAX_VALUE
二、Vector
public class Vector<E>
extends AbstractList<E>
implements List<E>, RandomAccess, Cloneable, java.io.Serializable
public Vector() { this(10);}和ArrayList一样，初始容量为10
protected Object[] elementData;
实现方式也是Object数组
public synchronized boolean add(E e) {
modCount++;
ensureCapacityHelper(elementCount + 1);
elementData[elementCount++] = e;
return true;
}所有方法由synchronized修饰
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省略之前的调用方法，直接来看最终实现吧
private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
private void grow(int minCapacity) {
// overflow-conscious code
int oldCapacity = elementData.length;
int newCapacity = oldCapacity + ((capacityIncrement > 0) ?
capacityIncrement : oldCapacity);
if (newCapacity - minCapacity < 0)
newCapacity = minCapacity;
if (newCapacity - MAX_ARRAY_SIZE > 0)
newCapacity = hugeCapacity(minCapacity);
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;
}
这里有一个capacityIncrement参数，这个参数是在构造Vector时一个选填参数，如果该值大于零，扩容后的容量就是 原容量 + capacityIncrement, 如果没有传入那么扩容容量 = 原容量 * 2
同样的，如果新生成的容量大于MAX_ARRAY_SIZE,容量定为Integer.MAX_VALUE,即最大值
需要注意的是，每次扩容都需要调用一次Arrays.copyOf方法,需要不断的重新实例化数组，所以在使用中最好直接指定容器大小
