What can I return nothing if a specific condition is not true

Question

I'm writing a Matrix class and I wrote a getNumber method which returns the number in a specific slot in the matrix. If the specific slot does not exists, what can I do? I got stuck here:

public int getNumber(int row, int column)
{  
    if (row < matrix.length && column < matrix[0].length) {
        return data[row][column];
    } else {
        //what now then?
    }
}

I don't want to return null after making the return type Integer because it doesn't feel like a nice design. What is the best way to do this? I considered ducking the IndexOutOfBoundsException but decided it is not a good idea because it doesn't change anything.

Answer 1

Since your code checks bounds on the input, you should throw, rather than returning:

public int getNumber(int row, int column) {  
    if (row >= matrix.length || column >= matrix[0].length) {
        throw new IndexOutOfBoundsException("("+row+", "+column+") is not a valid pair of indexes.");
    } 
    return data[row][column];
}

The reason you should throw, rather than returning silently, is that exceeding bounds is a programming error. The caller should fix it by not making the call in the first place, not by checking the return value.