CODEWITHSUNDEEP
javaexceptionmessagedefault
danger mouse
danger mouse

Reputation: 1497

Java, default exception messages

Given the following:

public abstract class Test {
    public static void main(String[] args) {
        int[] testArray = {6, 3, 2};
        System.out.println(testArray[3]);
    }
}

when I run the program I get:

Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 3
    at Test1.main(Test1.java:5)

In this case the JVM displays the index that is out of bounds i.e. 3.

This specific example aside, given that I choose not to catch an exception in a program's code:

  1. How can I find out, for any exception, either checked or unchecked, what the default message would be that the JVM would display?

  2. For a custom exception class that I write myself, and for an object of this class that I generate in my code using the 'throw' keyword (but, again, choose not to catch), can I set up a default message that the JVM would display?

Upvotes: 4

Views: 10278

Answers (4)

Lolo
Lolo

Reputation: 4347

  1. How can I found out, for any exception, either checked or unchecked, what the default message would be that the JVM would display?

As you might already suspect, the answer is "in general, you can't". Most of the time, the message is set from one of the constructors of the exception that takes a string message. If you're lucky, the message will be meaningful and provide useful information. Otherwise, as is common practice, the semantics of the exception will reside essentially in its class name and in the associated Javadoc. Also consider that exception messages are often localized.

  1. For a custom exception class that I write myself, and for an object of this class that I generate in my code using the 'throw' keyword (but, again, choose not to catch it), can I set up a default message that the JVM would display?

That's entirely up to you. You could setup a default message in the default constructor like this:

public class MyException extends Exception {
  public MyException() {
    super("my default message");
  }

  public MyException(String message) {
    super(message);
  }
}

Upvotes: 6

KnorpelSenf
KnorpelSenf

Reputation: 390

I am only able to answer your second question. In your Exception class (which should derive from java.lang.Exception) add (overwrite) the constructor accepting a String as an argument. Pass the message you want your thrown exception to have as a String to the new constructor et voilà → you got a personalized message for your exception. If you need a default message, just use this constructor from within the default one. Hope that helps.

Upvotes: 3

Alexander
Alexander

Reputation: 48232

There is Thread.setDefaultExceptionHandler, all the uncaught exceptions will go there, so you can provide your own exception handler as an argument to that method somewhere in the beginning of your program.

I think, you can also construct any exception yourself and see the message as follows

new IOException().getMessage()

though probably the message in that case will be empty, I didn't try

Upvotes: 3

Sunil Rajashekar
Sunil Rajashekar

Reputation: 350

Any exception that is of type or extends runtime exception is unchecked exception. Rest are checked exception.

You just need to extend runtime exception then you need not handle the exception that is thrown. And you can print default message for that exception by ovveriding getMessage method.

Upvotes: 1

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