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Thread: Exception Handling

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    Default Exception Handling

    I'm trying to traverse a String value HH:MM:SS to determine if the colons are missing, if there are any non-numeric values, or if the values are out of range. Later in the method I also created a String array to create an object that is returned by the method. That part I've already go figure out. I need to error check the text entered which is passed to the method as a String. So what I did was create a variable newTime to hold the passed value and I plan on traversing the String till I find characters that aren't numbers. My idea is to traverse the String to find any non-numeric characters and throw an exception as you can see. It's not processing correctly when this method is called. The exception is always thrown and it looks like my for loop isn't processing properly. Any help is ap

    String COLON = ":";

    try{
    for (int i = 0; i < newTime.length(); i++) {
    if (newTime.charAt(i) != COLON.charAt(0)) {

    JOptionPane.showMessageDialog(null, "Time format must be HH:MM:SS");
    throw new InvalidTime("Time delimiter must be a \"" + COLON + "\"");
    }
    }

    } //end try block

    catch(InvalidTime ex) {

    System.out.println("Exception: " + ex + " thrown");
    } // end catch block
    Last edited by hello_world; August 4th, 2011 at 08:18 PM.


  2. #2
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    Default Re: Exception Handling

    If you are talking about something like this
    throw new SomeException();
    System.out.println("Why doesn't this line work?");
    Surely it is obvious. The print statement will never be reached because the previous line threw an exception so execution has now gone to the exception handler and will never return to the print statement.

    Why are you always throwing an exception? You should only throw an exception in exceptional circumstances. That is only when a certain condition is met using an if statement.

    Another thought, have you considered a finally clause?
    Improving the world one idiot at a time!

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    Default Re: Exception Handling

    I'm trying to traverse a String value HH:MM:SS to determine if the colons are missing, if there are any non-numeric values, or if the values are out of range. Later in the method I also created a String array to create an object that is returned by the method. That part I've already go figure out. I need to error check the text entered which is passed to the method as a String. So what I did was create a variable newTime to hold the passed value and I plan on traversing the String till I find characters that aren't numbers. My idea is to traverse the String to find any non-numeric characters and throw an exception as you can see. It's not processing correctly when this method is called. The exception is always thrown and it looks like my for loop isn't processing properly. Any help is ap

    String COLON = ":";

    try{
    for (int i = 0; i < newTime.length(); i++) {
    if (newTime.charAt(i) != COLON.charAt(0)) {

    JOptionPane.showMessageDialog(null, "Time format must be HH:MM:SS");
    throw new InvalidTime("Time delimiter must be a \"" + COLON + "\"");
    }
    }

    } //end try block

    catch(InvalidTime ex) {

    System.out.println("Exception: " + ex + " thrown");
    } // end catch block

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    Default Re: Exception Handling

    The simplest and hardest way would be to use a regular expression. Simple because you could do it on one line. Hardest to get your head around it if you are not experienced with regular expressions.

    Alternatively you could use the String.split method and then validate each of the individual components (hour/minute/second).
    Last edited by Junky; August 4th, 2011 at 09:00 PM.
    Improving the world one idiot at a time!

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    Super Moderator Norm's Avatar
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    Default Re: Exception Handling

    If the format is NN:NN:NN then you could use substring to get each of the 3 groups of digits and do a parseInt to validate numberic and a charAt to check for the :

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    Default Re: Exception Handling

    Your logic is a bit out. You're testing every char in newTime against the first char in COLON - it would validate an input like "::::". Your technique for validating your input is ok - it's not as nice as using a regular expression or string splitting, but back in the day when we only had fixed-width fields (my lawn!), everybody did it your way. Since you know exactly what char should be at each position in your 8-char input, you could do it without a loop at all (the ugliest solution) with 8 if statements. if char at 0 is not 0-5, throw, if char at 2 is not ':' /* use apostrophes to make a constant char in Java */, throw - like that.

    You could construct some validation code that did use a for loop and an Array of Strings containing valid characters for each position in your field. That seems to be what you're attempting. In that case, you'd use a single index to pick both a character from newTime and its corresponding String containing valid chars, and use String.indexOf to check that the newTime char is in its corresponding validation String. That would work and might not look too ugly.

    I would habitually use a Pattern object (String.matches() does something similar) like Junky says for your particular problem - the expression for a fixed-width field with limited valid chars in each position is quite easy, once you get your head around the format.

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