1:Queue接口
继承接口Collection；
通常而言，顺序是FIFO，例外是优先级队列（顺序由指定的Comparator来决定）和栈(LIFO)增加了下面几个方法：
| Throws exception | Returns special value | |
| Insert | add(e) |
offer(e) |
| Remove | remove() |
poll() |
| Examine | element() |
peek() |
2:AbstractQueue
add()、remove()、element()是基于offer()、poll()、peek()来实现的； 代码如下:public abstract class AbstractQueue<E> extends AbstractCollection<E> implements Queue<E> {
protected AbstractQueue() {
}
public boolean add(E e) {
if (offer(e))
return true;
else
throw new IllegalStateException("Queue full");
}
public E remove() {
E x = poll();
if (x != null)
return x;
else
throw new NoSuchElementException();
}
public E element() {
E x = peek();
if (x != null)
return x;
else
throw new NoSuchElementException();
}
public void clear() {
while (poll() != null)
;
}
public boolean addAll(Collection<? extends E> c) {
if (c == null)
throw new NullPointerException();
if (c == this)
throw new IllegalArgumentException();
boolean modified = false;
Iterator<? extends E> e = c.iterator();
while (e.hasNext()) {
if (add(e.next()))
modified = true;
}
return modified;
}
}