PriorityBlockingQueue peek() method in Java

Last Updated : 26 Nov, 2018

The peek() method of PriorityBlockingQueue returns the element at head of the PriorityBlockingQueue. It retrieves the value of the head of LinkedBlockingQueue but does not remove it. If the PriorityBlockingQueue does not contains any element, then this method returns null. A PriorityBlockingQueue queue uses the same ordering rules as class PriorityQueue. Syntax:

public E peek()

Parameter: This method does not take any parameter. Returns: This method returns the head of the PriorityBlockingQueue. Below program illustrate peek() method of PriorityBlockingQueue. Example 1:

Java

// Java Program Demonstrate peek() // method of PriorityBlockingQueue  import java.util.concurrent.PriorityBlockingQueue;  public class GFG {     public static void main(String[] args)     {         // define capacity of PriorityBlockingQueue         int capacityOfQueue = 5;          // create object of PriorityBlockingQueue         PriorityBlockingQueue<Integer> PrioQueue             = new PriorityBlockingQueue<Integer>(capacityOfQueue);          // Add elements to PriorityBlockingQueue         PrioQueue.add(464161);         PrioQueue.add(416165);          // print PrioQueue         System.out.println("PrioQueue: " + PrioQueue);          // get head of PriorityBlockingQueue         int head = PrioQueue.peek();          // print head of PriorityBlockingQueue         System.out.println("Head of Queue: " + head);     } }

Output:

  PrioQueue: [416165, 464161]  Head of Queue: 416165

Example 2: To illustrate peek() method of PriorityBlockingQueue which contains list of names.

Java

// Java Program Demonstrate peek() // method of PriorityBlockingQueue  import java.util.concurrent.PriorityBlockingQueue;  public class GFG {     public static void main(String[] args)     {          // define capacity of PriorityBlockingQueue         int capacityOfQueue = 5;          // create object of PriorityBlockingQueue          PriorityBlockingQueue<String> names             = new PriorityBlockingQueue<String>(capacityOfQueue);          // Add names of students of girls college         names.add("Geeks");         names.add("forGeeks");         names.add("A");         names.add("Computer");         names.add("Portal");          // print PrioQueue         System.out.println("List of Names: " + names.toString());          // get head of PriorityBlockingQueue         String head = names.peek();          // print head of PriorityBlockingQueue         System.out.println("Head of Queue: " + head);          // remove one name from head         names.poll();         System.out.println("First Name from head is removed");          // print PrioQueue         System.out.println("List of Names: " + names.toString());          // get head of PriorityBlockingQueue         head = names.peek();          // print head of PriorityBlockingQueue         System.out.println("Head of Queue: " + head);     } }

Output:

  List of Names: [A, Computer, Geeks, forGeeks, Portal]  Head of Queue: A  First Name from head is removed  List of Names: [Computer, Portal, Geeks, forGeeks]  Head of Queue: Computer

Reference: https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/PriorityBlockingQueue.html#peek--

PriorityBlockingQueue peek() method in Java

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PriorityBlockingQueue peek() method in Java

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