What the?

package pl.codegym.task.task14.task1415;

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

/*
Usługi sprzątające
*/

public class Solution {
    public static void main(String[] args) {
        List<Apartment> apartments = new ArrayList<>();
        apartments.add(new OneRoomApt());
        apartments.add(new TwoRoomApt());
        apartments.add(new ThreeRoomApt());

        cleanAllApartments(apartments);
    }

    public static void cleanAllApartments(List<Apartment> apartments) {
        // Napisz tutaj swoją implementację Punktów 1-4

        for (int i = 0; i < apartments.size(); i++) {

            if (apartments.get(i) instanceof OneRoomApt) {
                ((OneRoomApt) apartments.get(i)).clean1Room();
            }
            else if (apartments.get(i) instanceof TwoRoomApt) {
                ((TwoRoomApt) apartments.get(i)).clean2Rooms();
            }
            else if (apartments.get(i) instanceof ThreeRoomApt) {
                ((ThreeRoomApt) apartments.get(i)).clean3Rooms();
            }
        }
    }

    static interface Apartment {
    }

    static class OneRoomApt implements Apartment {
        void clean1Room() {
            System.out.println("Posprzątano 1 pokój");
        }
    }

    static class TwoRoomApt implements Apartment {
        void clean2Rooms() {
            System.out.println("Posprzątano 2 pokoje");
        }
    }

    static class ThreeRoomApt implements Apartment {
        void clean3Rooms() {
            System.out.println("Posprzątano 3 pokoje");
        }
    }
}

public static void cleanAllApartments(List<Apartment> apartments) {

        for(int i = 0; i < apartments.size(); i ++) {
        if(apartments instanceof OneRoomApt){
            OneRoomApt oneRoomApt = new OneRoomApt();
            oneRoomApt.clean1Room();
        }
        if(apartments instanceof TwoRoomApt){
            TwoRoomApt twoRoomApt = new TwoRoomApt();
            twoRoomApt.clean2Rooms();
        }
        if(apartments instanceof ThreeRoomApt){
            ThreeRoomApt threeRoomApt = new ThreeRoomApt();
            threeRoomApt.clean3Rooms();
        }
        }
    }

OneRoomApt oneRoomApt = new OneRoomApt();
 oneRoomApt.clean1Room();