Declaring array size with variable leads to out of bounds exceptiong

Question

I\'m creating an int array secretNumber. When I declare the array size as a number, there\'s no out of bounds exception, but when I declare the array size with a variable (numDi

Answer 1

While we have already some clarification to the reason you got the exception there is still a question how to fix it and how to avoid such cases in future.

Let's go through your code step-by-step:

Engine engine = new Engine();

New engine object is created an all class variables instantiated to their default values. Default value for primitive int is 0;

At the moment of initialization you have:

public int numDigits; // 0
public int[] secretNumber = new int[numDigits]; // arrays object of size 0
public Random randomNumberGenerator; // null

How to proceed with that?

The issue is partially in object design - you need to identify the invariants that constrain the state variables. You need to set the size of the array during numDigits initialization:

public int[] secretNumber; // null at the moment of object initialization

public void setNumDigits() {
    Scanner setNumDigits = new Scanner(System.in);
    System.out.println("Enter the number of digits to use");
    numDigits = Integer.parseInt(setNumDigits.nextLine());
    secretNumber = new int[numDigits];
}