Java LinkedBlockingDeque peekFirst()用法及代码示例

LinkedBlockingDeque的peekFirst()方法返回Deque容器中的front元素，但不会删除它。如果容器为空，则返回null。

用法:

public E peekFirst()

参数：此方法不接受任何参数。

返回值：如果容器不为空，则此方法返回Deque容器中的front元素。如果容器为空，则返回null。

以下示例程序旨在说明LinkedBlockingDeque的peekFirst()方法：

示例1:

// Java Program Demonstrate peekFirst() 
// 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.peekFirst()); 
    } 
}

输出：

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

示例2:

// Java Program Demonstrate peekFirst() 
// 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); 
  
        // Print the queue 
        System.out.println("Linked Blocking Deque: " + LBD); 
  
        // empty deque 
        LBD.clear(); 
  
        System.out.println("Front element in Deque: " +  
                                          LBD.peekFirst()); 
    } 
}

输出：

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

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

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注：本文由纯净天空筛选整理自gopaldave大神的英文原创作品 LinkedBlockingDeque peekFirst() method in Java。非经特殊声明，原始代码版权归原作者所有，本译文未经允许或授权，请勿转载或复制。