Java ArrayDeque peek()方法

Java中的java.util.ArrayDeque.peek()方法是用来检索或获取Deque头部的元素的。检索到的元素不会被删除或从队列中移除，相反，该方法只是返回它。如果deque中没有元素，则会返回Null。

语法

Array_Deque.peek()

参数： 该方法不接受任何参数。

返回值： 该方法返回Deque头部的元素。

下面的程序说明了Java.util.ArrayDeque.peek()方法：

程序1 :

// Java code to illustrate peek()
import java.util.*;
  
public class ArrayDequeDemo {
    public static void main(String args[])
    {
        // Creating an empty ArrayDeque
        ArrayDeque<String> de_que = new ArrayDeque<String>();
  
        // Use add() method to add elements into the Deque
        de_que.add("Welcome");
        de_que.add("To");
        de_que.add("Geeks");
        de_que.add("4");
        de_que.add("Geeks");
  
        // Displaying the ArrayDeque
        System.out.println("Initial ArrayDeque: " + de_que);
  
        // Displaying the head
        System.out.println("The element at head is: " + 
                                           de_que.peek());
  
        // Displaying the ArrayDeque after operation
        System.out.println("Final ArrayDeque: " + de_que);
    }
}

输出。

Initial ArrayDeque: [Welcome, To, Geeks, 4, Geeks]
The element at head is: Welcome
Final ArrayDeque: [Welcome, To, Geeks, 4, Geeks]

程序2 :

// Java code to illustrate peek()
import java.util.*;
  
public class ArrayDequeDemo {
    public static void main(String args[])
    {
        // Creating an empty ArrayDeque
        ArrayDeque<Integer> de_que = new ArrayDeque<Integer>();
  
        // Use add() method to add elements into the Deque
        de_que.add(10);
        de_que.add(15);
        de_que.add(30);
        de_que.add(20);
        de_que.add(5);
  
        // Displaying the ArrayDeque
        System.out.println("Initial ArrayDeque: " + de_que);
  
        // Displaying the head
        System.out.println("The element at head is: " + 
                                           de_que.peek());
  
        // Displaying the ArrayDeque after operation
        System.out.println("Final ArrayDeque: " + de_que);
    }
}

输出。

Initial ArrayDeque: [10, 15, 30, 20, 5]
The element at head is: 10
Final ArrayDeque: [10, 15, 30, 20, 5]

程序3： 对于一个空deque。

// Java code to illustrate peek()
import java.util.*;
  
public class ArrayDequeDemo {
    public static void main(String args[])
    {
        // Creating an empty ArrayDeque
        ArrayDeque<Integer> de_que = new ArrayDeque<Integer>();
  
        // Displaying the ArrayDeque
        System.out.println("ArrayDeque: " + de_que);
  
        // Displaying the head
        System.out.println("The element at head is: " + de_que.peek());
    }
}

输出。

ArrayDeque: []
The element at head is: null