Performance cost of coding “exception driven development” in Java?

Question

Are there are any performance cost by creating, throwing and catching exceptions in Java?

I am planing to add \'exception driven development\' into a larger project.

Answer 1

Null objects is something which may be of help to you. I was reading Martin Fowler's book "Refactoring" the other day and it describes using a specific object which acts in the place of returning a null, saving you from having to check for NULL all the time.

I won't try to explain it here as it is described very well in the book.

Answer 2

I like this style of coding as it makes it very clear about what is going on from the point of view of someone using your API. I sometimes even name API methods getMandatoryUser(String) and getUserOrNull(String) to distinguish between methods that will never return null and those which can return null.

Regarding performance unless you're writing a very latency critical piece of code the performance overhead will be negligable. However, it's worth mentioning there are some best practices when it comes to try / catch blocks. For example, I believe Effective Java advocates creating a try / catch block outside of a loop to avoid creating it on each iteration; e.g.

boolean done = false;

// Initialise loop counter here to avoid resetting it to 0 if an Exception is thrown.
int i=0;    

// Outer loop: We only iterate here if an exception is thrown from the inner loop.
do {
  // Set up try-catch block.  Only done once unless an exception is thrown.    
  try {
    // Inner loop: Does the actual work.
    for (; i<1000000; ++i) {
      // Exception potentially thrown here.
    }

    done = true;
  } catch(Exception ex) {
    ... 
  }
} while (!done);