Question

I am often in a situation where I have a method where something can go wrong but an exception would not be right to use because it is not exceptional.

For example:

I am designing a monopoly game. The class Bank has a method buyHouse and a field which counts the number of houses left(there is 32 houses in monopoly). Something that could go wrong is a player buying a house when there is 0 left. How should I handle this. Here is 3 approaches I can come up with.

1. public void buyHouse(Player player, PropertyValue propertyValue)
{
    if(houseCount < 0) throw new someException;
    ....
    //Not really an exceptional situation
}

2. public boolean buyHouse(Player player, PropertyValue propertyValue)
{
    if(houseCount < 0) return false;
    ....
    //This I think is the most normal approach but changing something
    //and returning if it was a success seems bad practice to me.
}

3. public boolean housesLeft()
{
    if(houseCount > 0) return true;

    return false;

    //Introducing a new method. But now I expect the client to call this method
    //first before calling buyHouse(). 
}

What would you do?

Answer 1

I would do 3 and 1 together. The proper usage of the API is to check if there are houses left before buying one. If, however, the developer forgot to do so, then throw a runtime exception.

If it is a multi-threaded situation (where many people are buying a house simultaneously) it gets more complicated. In that case, I would indeed consider a checked exception, if not a tryToBuyAHouse method that returns a boolean, but a runtime exception on the buyHouse method.