Question

I currently have an ArrayList which houses the first 1000 prime numbers. I am able to successfully print the list to the console.

I am then applying the following method:

public static ScalesSolution RMHC(ArrayList<Double> weights, int n, int iter){

    private String scasol;

    ScalesSolution sol = new ScalesSolution(n);

    for(int i = 1; i <= iter; i++){

        double oldsol = sol.ScalesFitness(weights);

        sol.smallChange(n);
        sol.println();

        double newsol = sol.ScalesFitness(weights);

        if(newsol > oldsol){
            newsol = oldsol;
        }
    }
    return(sol);
}

Main method:

public static void main(String[] args){

    ArrayList<Double> primes = new ArrayList<Double>();

    primes.addAll(CS2004.ReadNumberFile("1000 Primes.txt"));

    RMHC(primes, 10, 50);

}

ScalesSolution class:

public class ScalesSolution{

public void smallChange(int n)
{
    Random rand = new Random();
    int p = (rand.nextInt(n) - 1);

    //Checks if p < 0.  If so, then p will not have 1 subtracted from it.
    if(p < 0){
        p = (rand.nextInt(n));
    }

    String x = new String();

    x = scasol.substring(0, p);

        if (scasol.charAt(p) == '0')
            scasol.replace('0', '1');
        else if (scasol.charAt(p) == '1')
            scasol.replace('1', '0');
            scasol = x;
}//End smallChange()

}

Whenever I call the method, however, I receive the following error no matter what I enter for the parameters. (FYI, ArrayList<Double> weights is the list of primes, int n is the size of the solution to look for and iter is the number of iterations that the algorithm will run for.)

Exception in thread "main" java.lang.StringIndexOutOfBoundsException: String index out of range: 6
at java.lang.String.substring(Unknown Source)
at ScalesSolution.smallChange(ScalesSolution.java:90)
at Lab8.RMHC(Lab8.java:15)
at Lab8.main(Lab8.java:46)

As mentioned above, the list contains 1000 elements (1000 – 1 indices), however I always receive the error above.

As you can see, it points to an error at index position 6, but there are 1000 - 1 index positions, so why does this happen? The index position changes with each run, but each and every time I run it, the error arises.

Thank you.

Answer 1

The problem is on this line:

x = scasol.substring(0, p);

The value of p (6) that you are passing in to the substring method is too large for the string scasol.