Log sorting - Custom sorting is not working

Question

Trying to sort the array 0f log versions in ascending order. I can get it to work by directly implementing Comparator as

 Arrays.sort(input, new CustomComparator())

and writing the same logic as below code(from the Parse class) in the CustomComparator class. However, when i try to sort it by adding the values in a Queue, the sorting does not work.

import java.util.*;

public class LogSorting {

    public static void main(String[] args) {
        String[] input = {"2.10.0", "1.0.100", "1.0.1", "1.1.100", "2.1.10", "1.1.1"};
        PriorityQueue<Parse> str = new PriorityQueue<>();
        for (String i : input) {
            String[] result = i.split("\\.");
            str.add(new Parse(Integer.parseInt(result[0]), Integer.parseInt(result[1]), Integer.parseInt(result[2])));
        }
        for (Parse p : str) {
            System.out.println(p.major + " " + p.minor + " " + p.patch);
        }
    }
}

class Parse implements Comparable<Parse> {
    int major;
    int minor;
    int patch;

    Parse(int major, int minor, int patch) {
        this.major = major;
        this.minor = minor;
        this.patch = patch;
    }

    public int compareTo(Parse p) {

        if (major == p.major && minor == p.minor)
            return Integer.compare(patch, p.patch);
        if (major == p.major)
            return Integer.compare(minor, p.minor);
        return Integer.compare(major, p.major);
    }
}

output

The output should be sorted as 1 0 1, 1 0 100, 1 1 1, 1 1 100, 2 1 10, 2 10 0

mystery · Accepted Answer · 2022-01-02 04:19:48Z

1

It's not a sorted array, so that you can just go from one element to the one with the lesser priority.The Iterator provided in method iterator() is not guaranteed to traverse the elements of the PriorityQueue in any particular order. If you need ordered traversal, consider using

Arrays.sort(pq.toArray()).

Or you can

    while (!str.isEmpty()) {
        Parse p = str.peek();
        str.remove();
        System.out.println(p.major + " " + p.minor + " " + p.patch);
    }

But this will empty the queue.

I do now know why are you using priority queue. If you just want sorted list then use List and then sort the list using comparable/comparator.

answered Jan 2, 2022 at 4:19

mystery

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1 Comment

dmah Over a year ago

Thanks a lot. This way of iterating through priorityqueue worked. Yeah, i had already implemented Arrays.sort() way, but just was not understanding what's wrong in this logic.

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