Java双向队列，用双向链表实现的

java双向队列，基于双向链表实现

package one;

import java.util.Iterator;

/*
*
* 双向队列，链表版
*
* */

public class Dequeue<Item> implements Iterable<Item> {

private Node first;//最左边的头节点
private Node last;//最右边的尾节点
private int N;//记录当前有多少的节点被存贮

private class Node{
private Node pre;
private Node next;
private Item item;
}

//返回存贮节点个数
public int size(){
return N;
}
//是否为空
private boolean isEmpty(){
return N==0;
}
//左进
public void pushLeft(Item item){
if(isEmpty()){
first=new Node();
first.item=item;
last=first;
}
else{
Node oldFirst=first;
first=new Node();
first.item=item;
first.next=oldFirst;
oldFirst.pre=first;
}
N++;
}
//右进
public void pushRight(Item item){
if(isEmpty()){
last=new Node();
last.item=item;
first=last;
}else{
Node oldLast=last;
last=new Node();
last.item=item;
last.pre=oldLast;
oldLast.next=last;
}
N++;
}
//左出
public Item popLeft() throws Exception{
//当为空时报错
if(isEmpty()){
throw new Exception("没有了");
}
Item item=first.item;
first=first.next;
if(N==1){
first=last=null;//当只有一个节点时也准备出的时候，last和first同时置null
}
else{
first.pre=null;//丢弃前一个节点
}
N--;
return item;
}
//右出，同理
public Item popRight() throws Exception{
if(isEmpty()){
throw new Exception("没有啦");
}
Item item=last.item;
last=last.pre;
if(N==1){
first=last=null;
}
else{
last.next=null;
}
N--;
return item;
}
//打印
public void print(){
Node current=first;
while(current!=null){
System.out.print(current.item+"  ");
current=current.next;
}
System.out.println();
}
//正向迭代
@Override
public Iterator<Item> iterator() {
return new Iterator<Item>(){
Node current=first;
@Override
public boolean hasNext() {
return current!=null;
}

@Override
public Item next() {
Item item=current.item;
current=current.next;
return item;
}
};
}

//反向迭代
public Iterable<Item> reverseIterator(){
return new Iterable<Item>(){
@Override
public Iterator<Item> iterator() {
return new Iterator<Item>(){
Node current=last;
@Override
public boolean hasNext() {
return current!=null;
}

@Override
public Item next() {
Item item=current.item;
current=current.pre;
return item;
}
};
}

};

}

//测试
public static void main(String[] args) throws Exception{
Dequeue<String> q=new Dequeue<String>();

q.pushLeft("a");
q.pushLeft("b");
q.pushLeft("c");
q.pushRight("c");
q.pushRight("b");
q.pushRight("a");
System.out.println("左出");
q.print();//c  b  a  c  b  a

q.popLeft();
q.print();//b  a  c  b  a
q.popLeft();
q.print();//a  c  b  a
q.popLeft();
q.print();//c  b  a
q.popLeft();
q.print();//b  a
q.popLeft();
q.print();//a
q.popLeft();
q.print();//空
//在来一遍

q.pushLeft("a");
q.pushLeft("b");
q.pushLeft("c");
q.pushRight("c");
q.pushRight("b");
q.pushRight("a");
System.out.println("右出");
q.print();//c  b  a  c  b  a

q.popRight();
q.print();//c  b  a  c  b
q.popRight();
q.print();//c  b  a  c
q.popRight();
q.print();//c  b  a
q.popRight();
q.print();//c  b
q.popRight();
q.print();//c
q.popRight();
q.print();

System.out.println("---------------");
q.pushLeft("a");
q.pushLeft("b");
q.pushLeft("c");
q.pushLeft("d");
q.pushLeft("e");
q.pushLeft("f");

System.out.println("正向排序");

for(String a:q){
System.out.print(a+"  ");
}
System.out.println();
System.out.println("反向排序");
for(String a:q.reverseIterator()){
System.out.print(a+"  ");
}
}
}