What is the best way to force a try block to break

Question

I have a try-catch block that I wish to break like a switch block but I couldn't find a recommended way of doing it. I'm fetching a lot of data in the try-catch block and wish to stop the fetching in between in case a certain condition is met. Just to get it working for now, I've deliberately forced the code to go into the catch block:

int i=0;
    try {
        //--do stuff----
        if(//-------is condition met?--------//)
            i = 1/0; // divide 1 by 0 -- a definite exception
    }
    catch (Exception e) {//---------do nothing---------//}

Is it safe to do this or should I go for another way?

EDIT:I'm fetching some xml data(actually, a lot). Depending on the internet connection, I need to stop the parsing after sometime(time-out) rather than go through the entire stream. I go through loops but I also make some calculations later. It doesn't make any sense to calculate with incomplete data, so I would prefer to just skip the whole thing.

Answer 1

Either break or throw will do what you want (and the throw would be preferable, you at least have some traceability as to WTH you're doing.

[edit]

what: try {
         System.out.println ("before break");
         break what;

      } catch (Exception e) {}
   }

[/edit]

Answer 2

Just put the rest of the fetching into an if block with the inverse condition:

//--do stuff----
if (!shouldStop) {
    // continue doing stuff
}

Answer 3

Throwing an Exception just to break is bad practice.

Would this work for your situation?

1. Put the code currently inside the try into another method, fetchLotsOfData(). It can still throw IOException or whatever is appropriate.
2. When you want to stop doing your thing fetching the data, just return. Perhaps returning some true/false or status for the success.

So your final code is something like

int recordsRead = -1;  // -1 means failure
try {
  recordsRead = fetchLotsOfData();
}
catch (IOException ioe) {
  // handle the exception
}

// process what you got...

Answer 4

I'm going to answer the "is is a good idea?" part of the question: No.

It is not a good idea to use exceptions to implement expected flow-of-control. It is possible, but not expected, just as it's possible to make all your variables Strings and implement all your data structures in arrays.

Try-blocks are for creating a scope boundary that has certain guarantees at termination (the catch and finally behavior). A code maintainer seeing:

try{ ... }catch(Exception x){} 

would very strongly tend to either rethrow x (perhaps wrapped) or eliminate the block entirely.

Try-blocks are not about what's inside their scope. That's what standard looping constructs and, better, functions are for. Your question simply goes away if you put your scope in a function:

RetVal doStuff(Arg arg){
    //--do stuff----
    if(//-------is condition met?--------//)
        return myResult;
}

Answer 5

This code smells of some anti-pattern but without more context we can't prescribe a better design. In general, you should only throw an exception for a truly exceptional condition in the state of your program. You should especially not throw an exception for normal (expected) control flow, instead you should use control flow statements such as loops (using break/continue) and return.

If you do wish to keep this structure (even though you should not) then I suggest explicitly throwing a special exception class to make it clear what you are doing, e.g.:

public static class ConditionMetException extends Exception { }

// ...
try {
  // do stuff
  if ( /* Is condition met? */ ) {
    throw new ConditionMetException();
  }
} catch (ConditionMetException cme) { /* Do nothing. */ }

But again, you're likely better off refactoring to use a loop and the built in break command.

Answer 6

Looking by your code

int i=0;
    try {
        //--do stuff----
        if(//-------is condition met?--------//)
            i = 1/0; // divide 1 by 0 -- a definite exception
    }
    catch (Exception e) {//---------do nothing---------//}

if the condition is not met? then you dont need to worry about using break, and

if the condition is met, there will be definitely an exception, and it is handled in catch(although you are not doing anything)