Create Java exception when String is entered instead of integer

Question

I have to create a calculator application at school and the calculator is working fine, but now I have to create an exception that shows a user friendly message when the user enters a string instead of an integer value.

This is the code I have now with a JFrame and everything:

private void minActionPerformed(java.awt.event.ActionEvent evt) {

    String invoerEen = getalEen.getText();
    int invoerEenDef =  Integer.parseInt(invoerEen);
    String invoerTwee = getalTwee.getText();
    int invoerTweeDef = Integer.parseInt(invoerTwee);

    int resultaatDef = invoerEenDef - invoerTweeDef;
    resultaat.setText(Integer.toString(resultaatDef));
}

private void plusActionPerformed(java.awt.event.ActionEvent evt) {
    String invoerEen = getalEen.getText();
    int invoerEenDef =  Integer.parseInt(invoerEen);
    String invoerTwee = getalTwee.getText();
    int invoerTweeDef = Integer.parseInt(invoerTwee);

    int resultaatDef = invoerEenDef + invoerTweeDef;
    resultaat.setText(Integer.toString(resultaatDef));
}

private void keerActionPerformed(java.awt.event.ActionEvent evt) {
    String invoerEen = getalEen.getText();
    int invoerEenDef =  Integer.parseInt(invoerEen);
    String invoerTwee = getalTwee.getText();
    int invoerTweeDef = Integer.parseInt(invoerTwee);

    int resultaatDef = invoerEenDef * invoerTweeDef;
    resultaat.setText(Integer.toString(resultaatDef));
}

private void delenActionPerformed(java.awt.event.ActionEvent evt) {
    String invoerEen = getalEen.getText();
    int invoerEenDef =  Integer.parseInt(invoerEen);
    String invoerTwee = getalTwee.getText();
    int invoerTweeDef = Integer.parseInt(invoerTwee);

    int resultaatDef = invoerEenDef / invoerTweeDef;
    resultaat.setText(Integer.toString(resultaatDef));
}

This code contains all the events and the actions they perform (the first one is for subtraction etc...). I use Netbeans as my development environment and I've tried adding try and catch statements like so:

try {
        String invoerEen = getalEen.getText();
        int invoerEenDef =  Integer.parseInt(invoerEen);
        String invoerTwee = getalTwee.getText();
        int invoerTweeDef = Integer.parseInt(invoerTwee);

        int resultaatDef = invoerEenDef - invoerTweeDef;
        resultaat.setText(Integer.toString(resultaatDef));
    }
catch(/* what do I put here? */) {
        // what do I do here?
}

So my question is, how do I create an exception for when a user enters a value that's not the correct return type (required: Integer, found: String).

Doubles or other return types are not important at the moment, only string.

Thanks in advance!

Michael Yaworski · Accepted Answer · 2013-12-05 22:10:46Z

2

To catch when there is a String entered (blank text counts too), use NumberFormatException:

catch (NumberFormatException n) {
     System.out.println("Please enter a number.");
}

To catch any error, use Exception:

catch (Exception e) {
     System.out.println("Error.");
}

You can combine these to catch different errors so you can handle them separately. For example:

try 
{
    String s = "hi";
    int i = Integer.parseInt(s); // will go into NumberFormatException n
    s = s.substring(-2); // will go into Exception e
}
catch (NumberFormatException n) {
    System.out.println("Please enter a number.");
}
catch (Exception e) {
    System.out.println("Unspecified error (not a NumberFormatException).");
}

edited Dec 5, 2013 at 22:10

answered Dec 5, 2013 at 21:50

Michael Yaworski

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Comments

Randa Sbeity · Accepted Answer · 2013-12-05 21:39:31Z

2

Use NumberFormatException. It's thrown when a method that converts a String to a number receives a String that it cannot be converted. like Integer.parseInt("sadfasd");

answered Dec 5, 2013 at 21:39

Randa Sbeity

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Ronald Meijboom · Accepted Answer · 2013-12-06 09:23:02Z

2

You can use NumberFormatException javaDoc or Exception e for generic exceptions and then print a message like: Invalid entry.

catch (NumberFormatException e) {
    System.out.println("Invalid entry, please enter a number");
}

edited Dec 6, 2013 at 9:23

answered Dec 5, 2013 at 21:44

Ronald Meijboom

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