Queue.java

import javax.xml.soap.Node;
import java.util.NoSuchElementException;

/**
 * Created by lxx on 2017/5/6.
 */
public class Queue<E> {

    private Node<E> first;
    private Node<E> last;
    private int size;

    private static class Node<E>{
        private E item;
        private Node<E> next;
    }
    public Queue(){
        first = null;
        last = null;
        size = 0;
    }
    public boolean isEmpty(){
        return first == null;
    }
    public int size(){
        return size;
    }
    public void enQueue(E data){
        Node<E> oldlast = last;
        last = new Node<E>();
        last.item = data;
        last.next = null;
        if(isEmpty()){
            first = last;
        }else {
            oldlast.next = last;
        }
        size++;
    }
    public E deQueue(){
        if(isEmpty()){
            throw new NoSuchElementException("queue is empty");
        }else{
            E item = first.item;
            first = first.next;
            size--;
            if(isEmpty()){
                last = null;
            }
            return item;
        }
    }


}