isInstance() on same class returns false during exception handling

Question

I am new to java and was trying to implement the isInstance() in a particular exception handling scenario.

try {

       ....
       ..//some condition
          throws MyException(); //  --> MyException extends RuntimeException

}catch(Exception e){
       if(e.getClass().isInstance(MyException.class))  // --> This returns false
                .. //do something
}

The above isInstance() returns false. When I debug, e.getClass() has a value :

in.soumav.exceptions.MyException (id=133)

and MyException.class has value:

in.soumav.exceptions.MyException (id=133)

Which concept am I missing at?

Is there a reason why you don't catch the specific Exceptions? Code-reuse? In that case check this: https://stackoverflow.com/questions/11211286/is-it-possible-in-java-to-catch-two-exceptions-in-the-same-catch-block — Jeppe, Jan 20 '19 at 11:33

score 2 · Accepted Answer · edited Jun 20 '20 at 09:12

2

You got it backwards.

It should be:

if (MyException.class.isInstance(e))

The Javadoc:

boolean java.lang.Class.isInstance(Object obj)

Determines if the specified Object is assignment-compatible with the object represented by this Class.

So, if you want to check if the exception instance reference by e is assignment compatible with the class MyException, you should pass e as an argument to MyException.class.isInstance().

As an alternative, you can use isAssignableFrom:

if (e.getClass().isAssignableFrom(MyException.class))

edited Jun 20 '20 at 09:12

Community

1
1

answered Jan 20 '19 at 11:29

Eran

387,369
54
702
768

`e instanceof MyException` would be better – Andrew Tobilko Jan 20 '19 at 12:15

score 2 · Answer 2 · answered Jan 20 '19 at 11:41

2

MyException.class is an instance of Class and not of MyException, so

MyException.class.isInstance(e)

should do it, but your purpose should be handled like:

try {

      ....
      ..//some condition
         throws MyException(); //  --> MyException extends RuntimeException

}catch(MyException e){
    ... //do something
}catch(Exception e){
    ...
}

answered Jan 20 '19 at 11:41

Turo

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Ups, i'm late, but i still think it should be handled with a catch block – Turo Jan 20 '19 at 11:44

isInstance() on same class returns false during exception handling

2 Answers2