Beginner: Assigning values to arrays in Java

Question

I am attempting to write a simple Genetic Algorithm in Java after reading a book on Machine Learning and have stumbled on the basics. I'm out of practice with Java so I'm probably missing something extremely simple.

Individual

public class Individual {

    int n;
    int[] genes = new int[500];
    int fitnessValue;

    public int getFitnessValue() {
        return fitnessValue;
    }

    public void setFitnessValue(int fitnessValue) {
        this.fitnessValue = fitnessValue;
    }

    public int[] getGenes() {
        return genes;
    }

    public void setGenes(int index, int gene) {
        this.genes[index] = gene;
    }

    public int getN() {
        return n;
    }

    public void setN(int n) {
        this.n = n;
    }

    // Constructor
    public Individual() {


    }

}

Population

import java.util.Random;

public class Population {

    public Population() {

    }

    public static void main(String[] args) {
        Random rand = new Random();
        int p = rand.nextInt(10);
        int n = rand.nextInt(10);

        Individual pop[] = new Individual[p];

        System.out.println("P is: " + p + "\nN is: " + n);

        for(int j = 0; j <= p; j++) {
            for(int i = 0; i <= n; i++) {
                pop[j].genes[i] = rand.nextInt(2);
            }
        }
    }

    public void addPopulation() {

    }
}

The aim of this code is to populate the Population and the Genes with a random number. Could someone please take a look at my code to see where I'm going wrong?

Answer 1

before

pop[j].genes[i] = rand.nextInt(2);

add

pop[j] = new Individual();

the elements of the array are null.

Answer 2

I believe you need to initialize pop[j] before doing pop[j].genes[i] = rand.nextInt();

    Individual pop[] = new Individual[p];

This just initializes the array, not the individual elements. Try to put pop[j] = new Individual() between your two loops.

Answer 3

What they said...

Also, do you mean to call your setGenes method, or do you just want to directly access the gene array.

Answer 4

From what I understand of your code I think you need to do this:

for(int j = 0; j <= p; j++) {
    pop[j] = new Individual();
    for(int i = 0; i <= n; i++) {
        pop[j].setGenes(i, rand.nextInt(2));
    }
}