Sort the Array having 0s, 1s, 2s and 3s only

package org.wesome.dsalgo;

import java.util.Arrays;

class CountPairsWithDifference {
    static int[] countPairsWithDifference(int[] arr) {
        int indx = 0, endIndx = arr.length - 1, midIndx = 0;
        while (midIndx <= endIndx) {
            System.out.println("array current element is = " + arr[midIndx]);
            if (arr[midIndx] == 0) {
                int temp = arr[indx];
                arr[indx] = arr[midIndx];
                arr[midIndx] = temp;
                indx++;
                midIndx++;
            }
            /*  if current element is 3, then swap it with endIndx */
            else if (arr[midIndx] == 3) {
                int temp = arr[midIndx];
                arr[midIndx] = arr[endIndx];
                arr[endIndx] = temp;
                endIndx--;
            }
            /*  in the current loop, only 0 and 3 will be considered, so for 1 and 2, just increment the index  */
            else if (arr[midIndx] == 1 || arr[midIndx] == 2) {
                System.out.println("array current element is = " + arr[midIndx] + " ignore right now");
                midIndx++;
            }
        }
        while (indx <= endIndx) {
            System.out.println("array current element is = " + arr[indx]);
            if (arr[indx] == 2) {
                int temp = arr[indx];
                arr[indx] = arr[endIndx];
                arr[endIndx] = temp;
                endIndx--;
            } else {
                indx++;
            }
        }
        System.out.println("arr = " + Arrays.toString(arr));
        return arr;
    }
}

package org.wesome.dsalgo;

import org.junit.jupiter.api.Assertions;
import org.junit.jupiter.api.Test;

import static org.wesome.dsalgo.CountPairsWithDifference.countPairsWithDifference;

class PairsWithDifferenceTest {

    @Test
    void countPairsWithDifferenceTest1() {
        int[] arr = {3, 2, 1, 0, 2, 3, 1, 0};
        Assertions.assertArrayEquals(new int[]{0, 0, 1, 1, 2, 2, 3, 3}, countPairsWithDifference(arr));
    }

    @Test
    void countPairsWithDifferenceTest2() {
        int[] arr = {3, 3, 3, 3, 2, 2, 2, 1, 1, 0};
        Assertions.assertArrayEquals(new int[]{0, 1, 1, 2, 2, 2, 3, 3, 3, 3}, countPairsWithDifference(arr));
    }
}

plugins {
    id 'java'
    id "io.freefair.lombok" version "6.4.1"
}

group = 'org.wesome'
version = '0.0.1-SNAPSHOT'
sourceCompatibility = JavaVersion.VERSION_1_8

configurations {
    compileOnly {
        extendsFrom annotationProcessor
    }
}

repositories {
    mavenCentral()
}

dependencies {
    testImplementation 'org.junit.jupiter:junit-jupiter:5.6.2'
}

test {
    useJUnitPlatform()
}