Queue element() method in Java (original) (raw)

Last Updated : 26 Sep, 2018

The element() method of Queue Interface returns the element at the front the container. It does not deletes the element in the container. This method returns the head of the queue.

This method differs from peek() only in that it throws an exception if this queue is empty.

Syntax:

E element()

Returns: This method returns the head of the Queue.

Exception: The function throws NoSuchElementException when the queue is empty and the function is called.

Below programs illustrate element() method of Queue:

Program 1: With the help of LinkedList.

import java.util.*;

public class GFG {

`` public static void main(String[] args)

`` throws IllegalStateException

`` {

`` Queue<Integer> Q

`` = new LinkedList<Integer>();

`` Q.add( 7855642 );

`` Q.add( 35658786 );

`` Q.add( 5278367 );

`` Q.add( 74381793 );

`` System.out.println( "Queue: " + Q);

`` System.out.println( "Queue's head: " + Q.element());

`` }

}

Output:

Queue: [7855642, 35658786, 5278367, 74381793] Queue's head: 7855642

Program 2: With the help of ArrayDeque.

import java.util.*;

public class GFG {

`` public static void main(String[] args)

`` throws IllegalStateException

`` {

`` Queue<Integer> Q

`` = new ArrayDeque<Integer>();

`` Q.add( 7855642 );

`` Q.add( 35658786 );

`` Q.add( 5278367 );

`` Q.add( 74381793 );

`` System.out.println( "Queue: " + Q);

`` System.out.println( "Queue's head: " + Q.element());

`` }

}

Output:

Queue: [7855642, 35658786, 5278367, 74381793] Queue's head: 7855642

Program 3: With the help of LinkedBlockingDeque.

import java.util.*;

import java.util.concurrent.LinkedBlockingDeque;

public class GFG {

`` public static void main(String[] args)

`` throws IllegalStateException

`` {

`` Queue<Integer> Q

`` = new LinkedBlockingDeque<Integer>();

`` Q.add( 7855642 );

`` Q.add( 35658786 );

`` Q.add( 5278367 );

`` Q.add( 74381793 );

`` System.out.println( "Queue: " + Q);

`` System.out.println( "Queue's head: " + Q.element());

`` }

}

Output:

Queue: [7855642, 35658786, 5278367, 74381793] Queue's head: 7855642

Program 4: With the help of ConcurrentLinkedDeque.

import java.util.*;

import java.util.concurrent.ConcurrentLinkedDeque;

public class GFG {

`` public static void main(String[] args)

`` throws IllegalStateException

`` {

`` Queue<Integer> Q

`` = new ConcurrentLinkedDeque<Integer>();

`` Q.add( 7855642 );

`` Q.add( 35658786 );

`` Q.add( 5278367 );

`` Q.add( 74381793 );

`` System.out.println( "Queue: " + Q);

`` System.out.println( "Queue's head: " + Q.element());

`` }

}

Output:

Queue: [7855642, 35658786, 5278367, 74381793] Queue's head: 7855642

Below programs illustrate exceptions thrown by this method:

Program 5: To show NoSuchElementException.

import java.util.*;

public class GFG {

`` public static void main(String[] args)

`` throws IllegalStateException

`` {

`` Queue<Integer> Q

`` = new LinkedList<Integer>();

`` Q.add( 7855642 );

`` Q.add( 35658786 );

`` Q.add( 5278367 );

`` Q.add( 74381793 );

`` System.out.println( "Queue: " + Q);

`` System.out.println( "Queue's head: " + Q.element());

`` Q.clear();

`` System.out.println( "Queue: " + Q);

`` try {

`` System.out.println( "Queue's head: " + Q.element());

`` }

`` catch (Exception e) {

`` System.out.println( "Exception: " + e);

`` }

`` }

}

Output:

Queue: [7855642, 35658786, 5278367, 74381793] Queue's head: 7855642 Queue: [] Exception: java.util.NoSuchElementException

Reference: https://docs.oracle.com/javase/8/docs/api/java/util/Queue.html#element–