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一、Deque在Java中的江湖地位

Collection是Deque的父类，所以Collection的方法Deque也可以拿来用：

Queue是Deque的父类，所以Queue的方法Deque也可以拿来用：

二、Deque自己特有的方法

Deque，双端队列之意。既然是双端队列，那么队首和队尾应该都可以：查看、添加、移除。事实上也的确如此，Deque中有大量关于头和尾的操作。

Deque的方法如下：

1、添加：addFirst、addLast、offerFirst、offerLast、push

a、代码import java.util.ArrayDeque;import java.util.Deque;public class Main {    public static void main(String[] args) {        Deque
   
     deque=new ArrayDeque<>();        deque.addFirst(1);        deque.addFirst(2);        System.out.println("deque:"+deque); //此时队列为：[2, 1]        deque.offerFirst(3); //在队首添加        System.out.println("deque:"+deque); //此时队列为：[3, 2, 1]        deque.push(4); //在队首添加        System.out.println("deque:"+deque); //此时队列为：[4, 3, 2, 1]        deque.offerLast(0); //在队尾添加        deque.addLast(-1); //在队尾添加        System.out.println("deque:"+deque); //此时队列为：[4, 3, 2, 1, 0, -1]    }}b、结果deque:[2, 1]deque:[3, 2, 1]deque:[4, 3, 2, 1]deque:[4, 3, 2, 1, 0, -1]
   

2、查看：peekFirst、peekLast、getFirst、getLast

a、代码import java.util.ArrayDeque;import java.util.Arrays;import java.util.Deque;public class Main {    public static void main(String[] args) {        Deque
   
     deque=new ArrayDeque<>();        deque.addAll(Arrays.asList(new Integer[]{1,2,3,4,5}));        System.out.println("deque:"+deque);        System.out.println("deque.peekFirst():"+deque.peekFirst());        System.out.println("deque.peekLast():"+deque.peekLast());        System.out.println("deque:"+deque);        System.out.println("deque.getFirst():"+deque.getFirst());        System.out.println("deque.getLast():"+deque.getLast());        System.out.println("deque:"+deque);    }}b、结果deque:[1, 2, 3, 4, 5]deque.peekFirst():1deque.peekLast():5deque:[1, 2, 3, 4, 5]deque.getFirst():1deque.getLast():5deque:[1, 2, 3, 4, 5]
   

区别：

import java.util.ArrayDeque;import java.util.Deque;public class Main {    public static void main(String[] args) {        Deque
   
     deque=new ArrayDeque<>();        System.out.println(deque.peekFirst()); //若空返回null        System.out.println(deque.peekLast()); //若空返回null        //System.out.println(deque.getFirst()); //若空抛异常：NoSuchElementException        //System.out.println(deque.getLast()); //若空抛异常：NoSuchElementException    }}
   

总结：peek好，无异常！

3、移除：removeFirst、removeLast、pollFirst、pollLast、pop

a、代码import java.util.ArrayDeque;import java.util.Arrays;import java.util.Deque;public class Main {    public static void main(String[] args) {        Deque
   
     deque=new ArrayDeque<>();        deque.addAll(Arrays.asList(new Integer[]{1,2,3,4,5,6,7,8}));        System.out.println("deque:"+deque);        System.out.println("deque.removeFirst():"+deque.removeFirst());        System.out.println("deque.removeLast():"+deque.removeLast());        System.out.println("deque:"+deque);        System.out.println("deque.pollFirst():"+deque.pollFirst());        System.out.println("deque.pollLast():"+deque.pollLast());        System.out.println("deque:"+deque);        System.out.println("deque.pop():"+deque.pop());        System.out.println("deque:"+deque);    }}b、结果deque:[1, 2, 3, 4, 5, 6, 7, 8]deque.removeFirst():1deque.removeLast():8deque:[2, 3, 4, 5, 6, 7]deque.pollFirst():2deque.pollLast():7deque:[3, 4, 5, 6]deque.pop():3deque:[4, 5, 6]
   

区别：

public class Main {    public static void main(String[] args) {        Deque
   
     deque=new ArrayDeque<>();        System.out.println(deque.pollFirst()); //若空返回null        System.out.println(deque.pollLast()); //若空返回null        System.out.println(deque.pop()); //若空抛异常：NoSuchElementException        //System.out.println(deque.removeFirst()); //若空抛异常：NoSuchElementException        //System.out.println(deque.removeLast()); //若空抛异常：NoSuchElementException    }}
   

总结：poll好，无异常！

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