what is comparable

what is comparable

  1월 31, 2022    Eunhan's library

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Hierarchy

package: java.lang.Comparable

Definition

Sorting interface that designed for a condition by overriding compareTo method. For example, you can sort list in ascending order of size.

about the compareTo() method

if compareTo() 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

customObject implements Comparable<>

Arrays.sort(customObject);
Collections.sort(customObject);

Example

import java.lang.Comparable;

public class customPoint implements Comparable<customPoint> {

    private int x = 0;
    private int y = 0;

    public customPoint(int x, int y) {
        this.x = x;
        this.y = y;

    }

    public int getX() {
        return x;
    }

    public int getY() {
        return y;
    }

    @Override
    public int compareTo(customPoint p2) {
        if (this.y > p2.y) {
            return 1; // y is in ascending order
        }
        return -1;
    }
}

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

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

        List<customPoint> pointList2 = new ArrayList<>();
        pointList2.add(new customPoint(10, 10));
        pointList2.add(new customPoint(1, 8));
        pointList2.add(new customPoint(5, 2));
        pointList2.add(new customPoint(1, 2));
        pointList2.add(new customPoint(5, 5));
        pointList2.add(new customPoint(10, 1));

        System.out.println("current list");
        for (customPoint temp : pointList2) {
            System.out.println("x: " + temp.getX() + "  " + "y: " + temp.getY());
        }

        System.out.println("sorted list");

        Collections.sort(pointList2);

        for (customPoint temp : pointList2) {
            System.out.println("x: " + temp.getX() + "  " + "y: " + temp.getY());
        }

    }

}

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: 10  y: 1
x: 1  y: 2
x: 5  y: 2
x: 5  y: 5
x: 1  y: 8
x: 10  y: 10