Question

I have a problem with sorting an ArrayList of my own objects.

My class of these objects looks like that:

public class Robal {
    int[] gen = new int[5];
    int fit;
    Random losuj = new Random();

    public Robal(int przelacz) {
        for (int i=0; i<5; i++ ) {
            gen[i]=losuj.nextInt(2);
        }
        fit=dopasuj(gen, przelacz);    
    }

    int dopasuj(int[] gen, int przelacz)    {
        int toDec=(gen[0]*1)+(gen[1]*2)+(gen[2]*4)+(gen[3]*8)+(gen[4]*16);
        return y(toDec, przelacz);
    }

    int y(int toDec, int przelacz) {
        if (przelacz == 1) {
            return toDec*toDec;
        } else if (przelacz == 2) {
            return 1;
        } else if(przelacz == 3) {
            return 1;
        } else if(przelacz == 4) {
            return 1;
        } else {
            return 1;
        }
    }

    void drukuj(int i) {
        System.out.println("Geny Robala "+i+": "+gen[0]+" "+gen[1]+" "+gen[2]+" "+gen[3]+" "+gen[4]+"\tfit:"+fit);
    }
}

and My Main class is:

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;

public class PE {

public static void main (String[] args){
ArrayList<Robal> Robale = new ArrayList<Robal>();
int i=0;
while(i!=5){
Robale.add(new Robal(1));
i++;
}
Robale.get(0).drukuj(1);
Robale.get(1).drukuj(2);
Robale.get(2).drukuj(3);
Robale.get(3).drukuj(4);

Collections.sort(Robale, new Comparator<Robal>() {
public int compare(Robal a, Robal b){
return a.fit - b.fit;
}
});

Robale.get(0).drukuj(1);
Robale.get(1).drukuj(2);
Robale.get(2).drukuj(3);
Robale.get(3).drukuj(4);


}


}

but most of the time the Data before and after sorting is not the same…
example result:

Geny Robala 1: 0 1 1 0 0 fit:36
Geny Robala 2: 1 0 1 0 1 fit:441
Geny Robala 3: 1 1 0 0 1 fit:361
Geny Robala 4: 0 1 1 1 0 fit:196
Geny Robala 1: 0 1 1 0 0 fit:36
Geny Robala 2: 0 0 0 1 0 fit:64
Geny Robala 3: 0 1 1 1 0 fit:196
Geny Robala 4: 1 1 0 0 1 fit:361

Answer 1

Are you sure you are not instantiating new Robal while sorting the list? that would cause the random values to shift