throwing RuntimeException with null value

[Mert Caliskan]

  
public class ExceptionTest {
 
public static void main(String[] args) {
try {
RuntimeException re = null;
throw re;
}
catch (RuntimeException e) {
System.out.println(e);
}
}
}
 

why does this evalute to NPE?

[Jesper de Jong]

Because that is just how Java works. According to the Java Language Specification section 14.18:

A throw statement first evaluates the Expression. If the evaluation of the Expression completes abruptly for some reason, then the throw completes abruptly for that reason. If evaluation of the Expression completes normally, producing a non-null value V, then the throw statement completes abruptly, the reason being a throw with value V. If evaluation of the Expression completes normally, producing a null value, then an instance V' of class NullPointerException is created and thrown instead of null. The throw statement then completes abruptly, the reason being a throw with value V'.

[ November 03, 2007: Message edited by: Jesper Young ]