LinkedBlockingDeque peekLast() method in Java

peekLast() 方法返回双端队列中的最后一个元素，但不删除它。如果容器为空，则返回 null 。

语法:

public E peekLast()

参数: 该方法不接受任何参数。

返回值: 如果双端队列不为空，则此方法返回双端队列中的最后一个元素。如果容器为空，则返回 false 。

以下程序说明了 LinkBlockingDeque 的 peekLast() 方法：

Program 1:

// Java Program Demonstrate peekLast()
// 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.addFirst(7855642);
        LBD.addFirst(35658786);
        LBD.addFirst(5278367);
        LBD.addFirst(74381793);

        // Print the queue
        System.out.println("Linked Blocking Deque: " + LBD);

        System.out.println("Front element in Deque: " + LBD.peekLast());
    }
}

Linked Blocking Deque: [74381793, 5278367, 35658786, 7855642]
Front element in Deque: 7855642

Program 2:

// Java Program Demonstrate peekLast()
// method of LinkedBlockingDeque
// 当 Deque 为空

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);

        // Print the queue
        System.out.println("Linked Blocking Deque: " + LBD);

        // 清空 deque
        LBD.clear();

        System.out.println("Front element in Deque: " + LBD.peekLast());
    }
}

Linked Blocking Deque: [7855642, 35658786, 5278367, 74381793]
Front element in Deque: null

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