When to throw runtime exception?

Question

Recently, I had interview with company and they gave me a coding problem. I was given program related to deck of cards and one of the methods was to shuffle the deck of cards. So I wrote the program as:

/** Shuffle the list of cards so that they are in random order   * @param d Deck of cards*/ public  static void shuffle(Deck d) {     if(d == null)         throw new IllegalArgumentException();     Random randomGenerator = new Random();     List<Card> cards = d.getDeckOfCards();   // cards is basically Linked List.. cards = new LinkedList<Cards>()     for(int i=0;i<cards.size();i++)     {         int randomNumber = randomGenerator.nextInt(52);         Card c1 = cards.remove(randomNumber);         Card c2 = cards.remove(0);         cards.add(0, c1);         cards.add(randomNumber,c2);     }         } 

In the above code, I have thrown IllegalArgumentException which I'm most doubtful about. Under what conditions should actually throw a runtime exception? Should we actually throw runtime exception?

Thanks

Answer 1

Should we actually throw runtime exception?

Yes, we should. Runtime exception serve a specific purpose - they signal programming problems that can be fixed only by changing code, as opposed to changing the environment in which the program runs.

Under what conditions should actually throw a runtime exception?

When you detect an error with the way your class or method is used, throw a runtime exception.

Generally, there are two categories of situations when you need to throw a runtime exception:

• Passing invalid parameter values - This is the most common cause of runtime exceptions. Most parameter validation exceptions should be runtime exceptions. Java provides several subclasses to signal these specific problems.
• Calling methods in a wrong sequence - This is another common cause. When certain methods cannot be called until a class finishes initialization or some other preparatory steps, calls at the wrong time should cause runtime exceptions.

In this sense, your code is fine: it fits squarely in the first category, i.e. passing invalid parameter values. One thing I would do slightly differently is adding a message to say which parameter had an invalid value, but in your case it is not critical, because there is only one parameter there.