Question

I’ve read pretty often, that using try-catch is quite slow compared to normal code.
Now I wonder if the number of caught exceptions affects the performance of the code or not.

So is

try{
  ...
}
catch(StrangeException e){
  ...
}

slower than

try{
  ...
}
catch(StrangeException e){
  ...
}
catch(MysteriousException e){
  ...
}
catch(FrighteningException e){
  ...
}

?

Of course I’m only referring to the code in the try-clause and if no exception is caught.

Answer 1

The cost of a try / catch block is essentially zero if no exceptions are actually thrown. The number of catch clauses makes no difference.

The cost of exceptions occurs only when they actually get thrown:

• Constructing the exception object is very expensive, because of the cost of the fillInStackTrace() step. This has to create and initialize a data structure containing key details of all frames on the current thread stack. In the worst case, there could be thousands of them.

• Throwing and catching exceptions is a bit expensive. In the worst case, the JVM needs to do the equivalent of an instanceof for each catch clause of each try / catch block. This is where having lots of catch clauses could make a difference to performance.