How to identify if a boolean array element has been changed?

Question

I'm trying to check if a particular boolean variable has been set to true or false explicitly by my code.

By default, a boolean array is initialized to false. So I'm unable to use it to verify my previous state as part of a DP problem. I thought of having a set containing the indices of all the modified elements. But I wanted to know if there was a more elegant way of doing this. Another way could be to stop default initialization though I can't seem to find how to do that.

public static boolean testMethod(int N) {
    boolean b[] = new boolean[N+1];
    return canWin(N,b);
}
public static boolean SubMethod(int N, boolean[] b){
    if(b[N] != null)// This is where I want to check(null check does not work)
        return b[N];

    for(int i = 1; i<= N/2; i++){
        if(N%i == 0){
            if(!SubMethod(N-i, b)){
                b[N] = true;
                return true;
            }
        }
    }
    b[N] = false;
    return false;
}

Answer 1

boolean is a primitive type. Primitive types in java are never null. By default boolean is set to false .

If you want to leverage null, use Boolean class

eg:

Boolean b[] = new Boolean[N+1];

Then,

if(b[N] != null)//

will work for you