javathrowable

Throwable getCause returns null

I am catching a Throwable error. 

catch (Throwable t){    
    System.out.println(t.getCause().getMessage());
}

When I put a breakpoint on a line System.out., and hover over (Eclipse) the t variable, Eclipse shows me the cause: java.lang.NoClassDefFoundError: myclass

But when I release the breakpoint I am getting null for t.getCause().

Why does it happen? How can I get the cause string.

UPDATE:

Same happens if I catch 

catch (NoClassDefFoundError e){
}
Solution

  • The answer is in the docs - Throwable#getCause:

    Returns the cause of this throwable or null if the cause is nonexistent or unknown. (The cause is the throwable that caused this throwable to get thrown.)

    So when you do:

    t.getCause().getMessage()

    It's like writing:

    null.getMessage()

    Which of course causes NullPointerException.

    You can simply do:

    catch (NoClassDefFoundError e){
   System.out.println(e.getMessage);
}