Question

Trying to get a random string out of ListArray on the button pressed. Always getting the same, second element. No matter how big the array is.

Here’s what I have on key pressed:

int randIndex = getRandomIndex(ListArray.size());
String chosenItem = ListArray.get(randIndex);

Method getRandomIndex is claimed beforehand and looks like this:

public int getRandomIndex(int size) {
        return (1+(int)Math.random()*size);
    };

Answer 1

The cast from int to double has precedence over the multiplication by size. When you cast Math.random() to an int, the decimal is dropped and the result is 0. Thus, getRandomIndex will always return 1.

In other words,

return (1 + (int) [some double variable] * size);

is the same as

return 1 + (0)*size;

which is the same as

return 1;

---

Fix it with:

private static final Random rand = new Random();

public int getRandomIndex(int size) {
    return rand.nextInt(size);
}

This is more readable and ensures an even distribution of random numbers.