Question

I wish to create a java method that returns an array of type: ABCout, where class ABCout is defined as:

public class ABCout {
    public int numOut;
    public double[] myArray;
}

and the java method is:

public ABCout[] GetABC( double myInput ) throws Exception {
   ABCout[] userABC = new ABCout[3];

   userABC[0].numOut = 10;
   userABC[0].myArray = new double[1];
   userABC[0].myArray[0] = myInput;
   /* here I only fill the 0'th element, but once working I will fill the others */

   return userABC;
}

but I’m getting the error: java.lang.NullPointerException : null

Anyone see what I’m doing wrong?

Answer 1

You initialized the array, but not the objects in it. You probably need to do:

ABCout[] userABC = new ABCout[3];
for (int i = 0; i < userABC.length; ++i) {
    userABC[i] = new ABCout();
}

Also, you need to instantiate myArray:

public class ABCout {
    public int numOut;
    public double[] myArray;

    public ABCout() {
        myArray = new double[10];
    }
}