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.
