LinkedList的几个元素操作方法

看完这几个方法的源码，大概我们知道了，LinkedList不仅实现了队列先进先出 （使用 add 和 remove ）也实现了栈的 先进后出 (使用pop和push)

• remove 移除头部元素 Retrieves and removes the head (first element) of this list. @throws NoSuchElementException if this list is empty

public E remove() {
        return removeFirst();
    }

• poll 移除头部元素 空队列返回null Retrieves and removes the head (first element) of this list.

public E poll() {
        final Node<E> f = first;
        return (f == null) ? null : unlinkFirst(f);
    }

• pop 栈顶取出 也就是从队列最前面取出 Pops an element from the stack represented by this list. In other words, removes and returns the first element of this list.@throws NoSuchElementException if this list is empty

public E pop() {
        return removeFirst();
    }

 public E removeFirst() {
        final Node<E> f = first;
        if (f == null)
            throw new NoSuchElementException();
        return unlinkFirst(f);
    }

• add 在队列最末尾添加Inserts the specified element at the specified position in this list.

public boolean add(E e) {
        linkLast(e);
        return true;
    }

• push 压如栈顶。也就是队列最前面插入 Pushes an element onto the stack represented by this list. In other words, inserts the element at the front of this list.

public void push(E e) {
        addFirst(e);
    }