Java中的LinkedBlockingDeque peek()方法

LinkedBlockingDeque 中的 peek() 方法返回Deque容器中的前面元素。如果容器为空，则返回 null 。

语法:

public E peek()

参数: 该方法不接受任何参数。

返回值: 如果Deque容器不为空，则该方法返回Deque容器中的前面元素。如果容器为空，则返回false。

下面的程序演示了LinkedBlockingDeque的peek()方法:

程序1:

// Java Program Demonstrate peek()
// method of LinkedBlockingDeque
  
import java.util.concurrent.LinkedBlockingDeque;
import java.util.*;
  
public class GFG {
    public static void main(String[] args)
  
    {
  
        // create object of LinkedBlockingDeque
        LinkedBlockingDeque<Integer> LBD
            = new LinkedBlockingDeque<Integer>();
  
        // Add numbers to end of LinkedBlockingDeque
        LBD.add(7855642);
        LBD.add(35658786);
        LBD.add(5278367);
        LBD.add(74381793);
  
        // 打印队列
        System.out.println("Linked Blocking Deque: " + LBD);
  
        System.out.println("Deque的前面元素: " + LBD.peek());
    }
}

Linked Blocking Deque: [7855642, 35658786, 5278367, 74381793]
Deque的前面元素: 7855642

程序2:

// Java Program Demonstrate peek()
// method of LinkedBlockingDeque
// when Deque is empty
  
import java.util.concurrent.LinkedBlockingDeque;
import java.util.*;
  
public class GFG {
    public static void main(String[] args)
  
    {
  
        // create object of LinkedBlockingDeque
        LinkedBlockingDeque<Integer> LBD
            = new LinkedBlockingDeque<Integer>();
  
        // Add numbers to end of LinkedBlockingDeque
        LBD.add(7855642);
        LBD.add(35658786);
        LBD.add(5278367);
        LBD.add(74381793);
  
        // 打印队列
        System.out.println("Linked Blocking Deque: " + LBD);
  
        // 清空Deque
        LBD.clear();
  
        System.out.println("Deque的前面元素: " + LBD.peek());
    }
}

Linked Blocking Deque: [7855642, 35658786, 5278367, 74381793]
Deque的前面元素: null

参考: https://docs.oracle.com/javase/7/docs/api/java/util/concurrent/LinkedBlockingDeque.html#peek()