Question

I have code that generates a random number form 0-1 3 times and I need it to be added to a variable so it turns into a binary number.So, in theory, this would run three times and possibly give me 101;

String storage = null;
        int i = 0;
        while (i < 3) {
            int binny = this.giveMeBinary();
            storage.concat(String.valueOf(binny));
            i++;
        }

        int ans = Integer.parseInt(storage);

But when I try and run this I get the NullPointerException error for storage. Is there a way to just “add” a string to the variable?

the method giveMeBinary just returns a 0 or a 1.

Answer 1

Your problem is that you are initializing the string to null. Doing something like so should solve your problem:

        String storage = "";
        int i = 0;
        while (i < 3) {
            int binny = this.giveMeBinary();
            storage += (String.valueOf(binny));
            i++;
        }

        int ans = Integer.parseInt(storage);

However, concatenating strings in such a manner is not recommended. What you can do is use a StringBuilder like so:

        StringBuilder storage = new StringBuilder();
        int i = 0;
        while (i < 3) {
            int binny = this.giveMeBinary();
            storage.append(String.valueOf(binny));
            i++;
        }

        int ans = Integer.parseInt(storage.toString());