ArrayDeque peek() Method in Java - GeeksforGeeks

10 Dec, 2018
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);    }}
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);    }}
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());    }}
ArrayDeque: []
The element at head is: null

Java - util package
Java-ArrayDeque
Java-Collections
Java-Functions
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Java-Collections
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