How can I get the name of the class that throws a custom made Exception

Question

I'm preparing a project for college where I need to write a custom made exception that will be thrown by a couple of classes in the same package when they were not initialized properly. The problem is that I must let the user know which of those classes wasn't initialized properly (and throwed the exception)... So I was thinking about something like this:

class InitializationException extends Exception {

private static final String DEFAULT_MSG =
            "This " + CLASSNAME-THROWINGME + " had not been initialized properly!";

    protected String msg;

InitializationException() {
    this.msg = DEFAULT_MSG;
}

    InitializationException(String msg) {
    this.msg = msg;
}
}

(btw, can it be achieved via reflection?)

You could extend `Exception` and add a field for the `.class` if the causing type. — le3th4x0rbot, May 02 '13 at 17:01

score 7 · Accepted Answer · answered May 02 '13 at 17:04

7

Look at Throwable.getStackTrace(). Each StackTraceElement has getClassName(). You can look at element [0] to determine the origination of the exception.

answered May 02 '13 at 17:04

Dilum Ranatunga

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Hot Licks · Answer 2 · 2013-05-02T17:13:33.863

1

Something like:

StackTraceElement[] trace = theException.getStackTrace();
String className = trace[0].getClassName();

(Though I'm not quite sure whether you want the first element or the last in the trace.)

(And note that you can create a Throwable and do getStackTrace() on it, without ever throwing it, to find out who called you (which would be trace element 1).)

edited May 02 '13 at 17:13

answered May 02 '13 at 17:06

Hot Licks

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You want the first one. The API says 'The zeroth element of the array (assuming the array's length is non-zero) represents the top of the stack, which is the last method invocation in the sequence. Typically, this is the point at which this throwable was created and thrown' – Dilum Ranatunga May 02 '13 at 17:08
@DilumRanatunga - Yeah, I'd have figured it out but I was racing to beat you. Didn't succeed, though. – Hot Licks May 02 '13 at 17:09
Nice tip about the unthrown `Throwable`. Answers the age old question "If an exception is instantiated but never thrown, was there really an exception?" The answer is "only if you called getStackTrace() to acknowledge its existence" :) – Dilum Ranatunga May 02 '13 at 17:16

score 1 · Answer 3 · 2013-05-02T17:18:40.130

1

I would just pass the throwing class into the constructor, like this:

public class InitializationException extends Exception {

    public InitializationException(Class<?> throwingClass) { ... }

    ...
}

edited May 02 '13 at 17:18

answered May 02 '13 at 17:08

score 1 · Answer 4 · answered May 02 '13 at 17:14

class InitializationException extends Exception {
    private final String classname;
    InitializationException(String msg, Object origin) {
        super(msg);
        this.classname = origin != null ? origin.getClass().toString() : null;
    }
    public String getClassname() {
        return this.classname;
    }
}

. . . . throw new InitializationException("Something went wrong", this);

MemLeak · Answer 5 · 2013-05-02T17:14:00.103

0

Its a workaround:

you could pass the classname within the Constructor, something like

throw new  InitializationException(getClass().getName());

or may be call the class like

throw new InitializationException(this);

and handle the name extraction in your excpetin class

 InitializationExcpetion(Object context){ 
this.name = getClass().getName() 
}

edited May 02 '13 at 17:14

answered May 02 '13 at 17:07

MemLeak

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`getEnclosingClass()` is used for inner classes. If the class constructing the exception is not an inner class, this will be `null`. See http://docs.oracle.com/javase/7/docs/api/java/lang/Class.html#getEnclosingClass() – Dilum Ranatunga May 02 '13 at 17:10

score 0 · Answer 6 · answered May 02 '13 at 17:15

The answer is you force the class throwing the exception to tell the exception which class it is:

public class InitializationException extends Exception {

    public InitializationException(Class<?> c) {
        super( "The class " + c.getName()+ " had not been initialized properly!");
    }
}

How can I get the name of the class that throws a custom made Exception

6 Answers6