ArrayDeque peek() Method in Java

The java.util.ArrayDeque.peek() method in Java is used to retrieve or fetch the element at the head of the Deque. The element retrieved does not get deleted or removed from the Queue instead the method just returns it. If no element is present in the deque then Null is returned.

Syntax:

Array_Deque.peek()

Parameters: The method does not take any parameter.

Return Value: The method returns the element at the head of the Deque.

Below programs illustrate the Java.util.ArrayDeque.peek() method:
Program 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);
    }
}

Output:

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

Program 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);
    }
}

Output:

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

Program 3: For an empty 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());
    }
}

Output:

ArrayDeque: []
The element at head is: null