what is comparator

what is comparator

  1월 31, 2022    Eunhan's library

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Hierarchy

package: java.util.Comparator

Definition

Sorting interface that designed for mutiple special conditions by creating compare method. For example, you can sort list in ascending order of size and descending order of letters.

about the compare() method

if compare() method return positive number, swap the input parameters
else will be remain same

if First parameter < second parameter, negative
if First parameter == second parameter, 0
if First parameter > second parameter, positive

How to use

MyComparator implements Comparator<>

MyComparator myComparator = new MyComparator();
Arrays.sort(array, myComparator);
Collections.sort(list, myComparator);

Example

import java.awt.*;
import java.util.Comparator;

public class MyComparator implements Comparator<Point> {

    public int compare(Point p1, Point p2) {
        if (p1.x > p2.x) {
            return 1; // x is in ascending order
        } else if (p1.x == p2.x) {
            if (p1.y < p2.y) { // y is in descending order
                return 1;
            }
        }
        return -1;
    }
}

import java.awt.*;
import java.util.List;
import java.util.ArrayList;
import java.util.Collections;


public class Main {
    public static void main(String[] args) {

        List<Point> pointList = new ArrayList<>();
        pointList.add(new Point(10, 10));
        pointList.add(new Point(1, 8));
        pointList.add(new Point(5, 2));
        pointList.add(new Point(1, 2));
        pointList.add(new Point(5, 5));
        pointList.add(new Point(10, 1));

        System.out.println("current list");
        for (Point temp : pointList) {
            System.out.println("x: " + temp.x + "  " + "y: " + temp.y);
        }

        MyComparator myComparator = new MyComparator();
        Collections.sort(pointList, myComparator);

        System.out.println("sorted list");
        for (Point temp : pointList) {
            System.out.println("x: " + temp.x + "  " + "y: " + temp.y);
        }

    }

}

Result

current list
x: 10  y: 10
x: 1  y: 8
x: 5  y: 2
x: 1  y: 2
x: 5  y: 5
x: 10  y: 1
sorted list
x: 1  y: 8
x: 1  y: 2
x: 5  y: 5
x: 5  y: 2
x: 10  y: 10
x: 10  y: 1