线性表之队列API设计思路

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队列是一种基于先进先出(FIFO)的数据结构，是一种只能在一端进行插入,在另一端进行删除操作的特殊线性表，它按照先进先出的原则存储数据，先进入的数据，在读取数据时先读被读出来。

1、队列的API设计

public class Queue<T> implements Iterable<T>{

    private int size;

    private Node head;

    private Node last;

    public Queue() {
        size = 0;
        head = new Node(null,null);
        last = null;
    }

    public boolean isEmpty(){
        return size == 0;
    }

    public int size(){
        return size;
    }

    /**
     * 插入元素到队列
     * @param t
     */
    public void enqueue(T t){
        //如果链尾都为空
        if(null == last){
            last = new Node(t,null);
            head.next = last;
        }else {
            //如果链尾不为空
            Node pre = last;
            last = new Node(t, null);
            pre.next = last;
        }
        size++;
    }

    /**
     * 取出元素
     * @return
     */
    public T dequeue(){
        if (isEmpty()){
            return null;
        }
        Node oldHead = head.next;
        head.next = oldHead.next;
        size--;
        if (isEmpty()){
            last = null;
        }
        return oldHead.item;
    }

    /**
     * 节点类
     */
    private class Node{
        public T item;
        public Node next;

        public Node(T item, Node next) {
            this.item = item;
            this.next = next;
        }
    }

    @Override
    public Iterator<T> iterator() {
        return new QIterator();
    }

    public class QIterator implements Iterator<T>{

        private Node n = head;

        @Override
        public boolean hasNext() {
            return n.next != null;
        }

        @Override
        public T next() {
            Node node = n.next;
            n = n.next;
            return node.item;
        }
    }
}