Q from Dan'S Exception

[Mandeep Sethi]

Hi Guys
chk this
class RedException extends Exception {}
class BlueException extends Exception {}
class White {
void m1() throws RedException {throw new RedException();}
public static void main (String[] args) {
White white = new White();
int a,b,c,d;
a = b = c = d = 0;
try {white.m1();a++;}
catch (RedException e) {b++;}
catch (BlueException e) {c++;}
finally {d++;}
System.out.print(a+","+b+","+c+","+d);
}
}

What is the result of attempting to compile and run the program?
Dans answer is
A compile-time error is generated because the second catch clause attempts to catch an exception that is never thrown in the try block.
My doubt is whether its a neccessity to throw only those exceptions that are stated to be thrown
Best
Mandeep

[Francis Siu]

hi Mandeep
My doubt is whether its a neccessity to throw only those exceptions that are stated to be thrown
I think it is a tricky question
You can help me to check it out too.
If you claim to throw Unchecked exception that is not necessary to explicit be thrown,when you whether want to throw it or not.
But checked exception is necessary to explicit be thrown and catched it,when you first claim it.
if you change a little bit of the following case,I hope that you can find out the answer.
First case:

void m1() throws RedException,BlueException 
{
 if(something==true)
  throw new RedException();
 else
  throw new RuntimeException();
}
 

Second case:

void m1() throws RedException,BlueException 
{
 if(something==1)
  throw new RedException();
 else if(something==2)
  throw new BlueException();
 else
  throw new RuntimeException();
}

Hope you find out the answer

[Brian Joseph]

I came across this question as well. The compiler is aware of which methods throw exceptions and it can catch unnecessary code like this.
However, there is one exception to this rule (no pun intended).
You can catch the generic Exception without a compiler error, even if nothing within the try block throws an exception. Otherwise, the compiler will bark at you if you try to catch an exception.

try {
//Do nothing
}
catch(Exception e) { //Legal }
try {
//Do nothing
}
catch(BlueException e) { //Illegal }

[ June 16, 2003: Message edited by: Brian Joseph ]