Queue peek() method in Java
The peek() 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. The method does not throws an exception when the Queue is empty, it returns null instead.
Syntax:
E peek()
Returns: This method returns the head of the Queue, it returns false when the Queue is empty
Below programs illustrate peek() 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.peek());
System.out.println( "Queue: " + Q);
}
}
|
Output:
Queue: [7855642, 35658786, 5278367, 74381793]
Queue's head: 7855642
Queue: [7855642, 35658786, 5278367, 74381793]
Program 2: To demonstrate peek() method of Queue when Queue is empty
import java.util.*;
public class GFG {
public static void main(String[] args)
throws IllegalStateException
{
Queue<Integer> Q
= new LinkedList<Integer>();
System.out.println( "Queue: " + Q);
System.out.println( "Queue's head: " + Q.peek());
}
}
|
Output:
Queue: []
Queue's head: null
Program 3: 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.peek());
}
}
|
Output:
Queue: [7855642, 35658786, 5278367, 74381793]
Queue's head: 7855642
Program 4: 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.peek());
}
}
|
Output:
Queue: [7855642, 35658786, 5278367, 74381793]
Queue's head: 7855642
Program 5: 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.peek());
}
}
|
Output:
Queue: [7855642, 35658786, 5278367, 74381793]
Queue's head: 7855642
Reference: https://docs.oracle.com/javase/8/docs/api/java/util/Queue.html#peek–
Last Updated :
26 Sep, 2018
Like Article
Save Article
Share your thoughts in the comments
Please Login to comment...