threads

PriorityQueue example

In this example we shall show you how to use a PriorityQueue. To use a PriorityQueue one should perform the following steps:

  • Create a new Comparator for Integer objects, that is a comparison function, which imposes a total ordering on some collection of objects.
  • Override the compare(Integer i, Integer j) method of Comparator in order to make a specified comparison.
  • Create a new PriorityQueue with a specified initial capacity, that orders its elements according to the specified comparator.
  • Use offer(Integer e) API method of PriorityQueue to insert an element to the PriorityQueue for comparison.
  • Use poll() API method of PriorityQueue to get the head of the queue,

as described in the code snippet below.  

package com.javacodegeeks.snippets.core;

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.util.Scanner;
import java.util.concurrent.ArrayBlockingQueue;
import java.util.concurrent.BlockingQueue;

import java.util.Comparator;
import java.util.PriorityQueue;
import java.util.Queue;

public class PriorityQueueExample {

    public static void main(String[] args) {


  PriorityQueue<Integer> pq =


    new PriorityQueue<Integer>(20,


    new Comparator<Integer>() {



@Override



  public int compare(Integer i, Integer j) {




int result = i % 2 - j % 2;




if (result == 0) {




    result = i - j;




}




return result;



  }


    });


  for (int i = 0; i < 20; i++) {


pq.offer(20 - i);

  }


  for (int i = 0; i < 20; i++) {


System.out.println(pq.poll());

  }
    }
}

Output:

2
4
6
8
10
12
14
16
18
20
1
3
5
7
9
11
13
15
17
19

  
This was an example of how to use a PriorityQueue in Java.

Ilias Tsagklis

Ilias is a software developer turned online entrepreneur. He is co-founder and Executive Editor at Java Code Geeks.
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