Java LinkedBlockingDeque peek() 方法

2025 年 3 月 21 日 | 阅读 2 分钟

LinkedBlockingDeque 类的 peek() 方法检索此双端队列对应的队列的头部，但不会将其移除。如果此双端队列为空，则该方法返回 null。

语法

参数

不适用

指定者：

LinkedBlockingDeque 类的 peek() 方法由以下接口指定：

Queue<E> 接口中的 peek() 方法。
Deque<E> 接口中的 peek() 方法。
BlockingDeque<E> 接口中的 peek() 方法。

返回值

peek() 方法返回此双端队列的头部，如果此双端队列为空，则返回 null。

示例 1

import java.util.concurrent.LinkedBlockingDeque;
public class LinkedBlockingDequePeekExample1 {
    public static void main(String[] args) {
        int capacity =100;
        LinkedBlockingDeque<String> deque = new LinkedBlockingDeque<String>(capacity);

        deque.add("Vishakha");
        deque.add("Mansi");
        deque.add("Ujjwal");
        deque.add("Ankit");

        //peek() method will retrieve the head of the deque
        System.out.println("Head of deque      : "+deque.peek());
        
        //peek() will not remove the head from the deque
        System.out.println("Deque after peek() : "+deque);
    }
}

输出

Head of deque      : Vishakha
Deque after peek() : [Vishakha, Mansi, Ujjwal, Ankit]

示例 2

import java.util.concurrent.LinkedBlockingDeque;
class Student {
    int marks;
    String name;
    public Student(int marks, String name) {
        this.marks = marks;
        this.name = name;
    }
   public String toString(){

        return this.name+" got "+ this.marks +" marks.";
   }
}

public class LinkedBlockingDequePeekExample2 {
    public static void main(String[] args) {

        Student student1 = new Student(97,"Ravina");
        Student student2 = new Student(87,"Jitesh");
        Student student3 = new Student(77,"Ajay");

        int capacity =100;
        LinkedBlockingDeque<Student> deque = new LinkedBlockingDeque<Student>(capacity);

        deque.add(student1);
        deque.add(student2);
        deque.add(student3);

         for (Student xyz : deque){
             System.out.println(xyz);
         }

        System.out.println();
       System.out.println("Topper of the class is "+deque.peek().name);
    }
}

输出

Ravina got 97 marks.
Jitesh got 87 marks.
Ajay got 77 marks.

Topper of the class is Ravina

示例 3

import java.util.concurrent.LinkedBlockingDeque;
public class LinkedBlockingDequePeekExample3{
    public static void main(String[] args) {
        int capacity =100;
        LinkedBlockingDeque<String> deque = new LinkedBlockingDeque<String>(capacity);
        deque.add("Harsh");
        deque.add("Arun");
        deque.add("Vaibhav");
        deque.add(null);
        deque.clear();
        String val = deque.peek();
        System.out.println("Head of deque is : "+val);
    }
}

输出

Exception in thread "main" java.lang.NullPointerException
	at java.util.concurrent.LinkedBlockingDeque.offerLast(LinkedBlockingDeque.java:357)
	at java.util.concurrent.LinkedBlockingDeque.addLast(LinkedBlockingDeque.java:334)
	at java.util.concurrent.LinkedBlockingDeque.add(LinkedBlockingDeque.java:633)
	at com.TpointTech.LinkedBlockingDequePeekExample3.main(LinkedBlockingDequePeekExample3.java:10)

下一主题Java Linkedblockingdeque

Java LinkedBlockingDeque peek() 方法

语法

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示例 1

示例 2

示例 3

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Java LinkedBlockingDeque peek() 方法

语法

参数

指定者：

返回值

示例 1

示例 2

示例 3

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