The java.util.ArrayDeque.peekFirst() method in Java is used to retrieve or fetch the first element 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 or it is empty, then Null is returned.
Syntax:Array_Deque.peekFirst()
Parameters: The method does not take any parameter.
Return Value: The method returns the first element of the Deque.Below programs illustrate the Java.util.ArrayDeque.peekFirst() method:
Program 1:Java// Java code to illustrate peekFirst()importjava.util.*;publicclassArrayDequeDemo{publicstaticvoidmain(Stringargs[]){// Creating an empty ArrayDequeDeque<String>de_que=newArrayDeque<String>();// Use add() method to add elements into the Dequede_que.add("Welcome");de_que.add("To");de_que.add("Geeks");de_que.add("4");de_que.add("Geeks");// Displaying the ArrayDequeSystem.out.println("Initial ArrayDeque: "+de_que);// Displaying the first elementSystem.out.println("The first element is: "+de_que.peekFirst());// Displaying the ArrayDeque after operationSystem.out.println("Final ArrayDeque: "+de_que);}}Output:Initial ArrayDeque: [Welcome, To, Geeks, 4, Geeks]The first element is: WelcomeFinal ArrayDeque: [Welcome, To, Geeks, 4, Geeks]
Program 2:Java// Java code to illustrate peekFirst()importjava.util.*;publicclassArrayDequeDemo{publicstaticvoidmain(Stringargs[]){// Creating an empty ArrayDequeDeque<Integer>de_que=newArrayDeque<Integer>();// Use add() method to add elements into the Dequede_que.add(10);de_que.add(15);de_que.add(30);de_que.add(20);de_que.add(5);// Displaying the ArrayDequeSystem.out.println("Initial ArrayDeque: "+de_que);// Displaying the first elementSystem.out.println("The first element is: "+de_que.peekFirst());// Displaying the ArrayDeque after operationSystem.out.println("Final ArrayDeque: "+de_que);}}Output:Initial ArrayDeque: [10, 15, 30, 20, 5]The first element is: 10Final ArrayDeque: [10, 15, 30, 20, 5]
Program 3: For an empty deque:
Java// Java code to illustrate peekFirst()importjava.util.*;publicclassArrayDequeDemo{publicstaticvoidmain(Stringargs[]){// Creating an empty ArrayDequeArrayDeque<Integer>de_que=newArrayDeque<Integer>();// Displaying the ArrayDequeSystem.out.println("ArrayDeque: "+de_que);// Displaying the first elementSystem.out.println("The first element is: "+de_que.peekFirst());}}Output:ArrayDeque: []The first element is: null
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