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Should try...catch go inside or outside a loop?

Asked 2008-09-26T19:52:30.143
217

I have a loop that looks something like this:

for (int i = 0; i < max; i++) {
    String myString = ...;
    float myNum = Float.parseFloat(myString);
    myFloats[i] = myNum;
}

This is the main content of a method whose sole purpose is to return the array of floats. I want this method to return null if there is an error, so I put the loop inside a try...catch block, like this:

try {
    for (int i = 0; i < max; i++) {
        String myString = ...;
        float myNum = Float.parseFloat(myString);
        myFloats[i] = myNum;
    }
} catch (NumberFormatException ex) {
    return null;
}

But then I also thought of putting the try...catch block inside the loop, like this:

for (int i = 0; i < max; i++) {
    String myString = ...;
    try {
        float myNum = Float.parseFloat(myString);
    } catch (NumberFormatException ex) {
        return null;
    }
    myFloats[i] = myNum;
}

Is there any reason, performance or otherwise, to prefer one over the other?

Edit: The consensus seems to be that it is cleaner to put the loop inside the try/catch, possibly inside its own method. However, there is still debate on which is faster. Can someone test this and come back with a unified answer?

java performance loops try-catch
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3 Answers

1

The whole point of exceptions is to encourage the first style: letting the error handling be consolidated and handled once, not immediately at every possible error site.

answered 2008-09-26T23:11:28.013
1

put it inside. You can keep processing (if you want) or you can throw a helpful exception that tells the client the value of myString and the index of the array containing the bad value. I think NumberFormatException will already tell you the bad value but the principle is to place all the helpful data in the exceptions that you throw. Think about what would be interesting to you in the debugger at this point in the program.

Consider: 

try {
   // parse
} catch (NumberFormatException nfe){
   throw new RuntimeException("Could not parse as a Float: [" + myString + 
                              "] found at index: " + i, nfe);
}

In the time of need you will really appreciate an exception like this with as much information in it as possible.

answered 2008-10-01T05:23:00.147
1

Another aspect not mentioned in the above is the fact that every try-catch has some impact on the stack, which can have implications for recursive methods.

If method "outer()" calls method "inner()" (which may call itself recursively), try to locate the try-catch in method "outer()" if possible. A simple "stack crash" example we use in a performance class fails at about 6,400 frames when the try-catch is in the inner method, and at about 11,600 when it is in the outer method.

In the real world, this can be an issue if you're using the Composite pattern and have large, complex nested structures.

answered 2010-03-11T19:06:16.940

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