Try Catch Finally - Voodoo Question

[Jason Keating]

Hi, I've another question, I've googled this one and fiddled with the code till I'm blue in the face but I'm still confused.

With regard to the code below, I thought flow would be as follows.

main()->raid()->try->Exception()->catch->Arithmetic Exception->finally

But I was wrong, the arithmetic exception is not reported, if I comment out the finally an arithmetic exception is thrown.

To me it appears this may happen because the arithmetic exception is unchecked and the finally must run therefore the runtime exception is ignored ?

Anyone able to confirm this or set me straight please?

Thanks in advance,

Jason

  class Test {
 
static String raid ( ) {
try
{
throw new Exception ( ) ;
}
catch ( Exception e )
{
int i = 10/0;
return " Error " ;
}
finally
{
return " Peace " ;
}
}
 
public static void main ( String args [ ] ) {
System . out . println ( raid ( ) ) ;
}
};
  

Output

Peace

[ February 09, 2006: Message edited by: Jason Keating ]

[Anju sethi]

return in finally clause nullify exception

[Swati Thorve]

Hi,

U r flow of execution is very correct,

main()->raid()->try->Exception()->catch->Arithmetic Exception->finally

But here look at the one thing, though in catch block arithmetic exception is thrown, control goes to finally block, as it must be executed in any condition. And in the finally block there is return statement, so whenever there is return statement in finally block all the previously thrown exceptions are ignored & the corresponding o/p i.e "peace" is printed.

[Raghusham Sankargal]

Hi,
The return statement outclasses the other return statements. As a result the return statement is executed[That is equivalent to the normal termination of the function]. The exception is not seen. You will get exception even if you have the finally block and not any return statement. Two things to consider is that "its neither the return nor the finally that does the work, but infact both does the work".

[Naren Chivukula]

Hi,

so whenever there is return statement in finally block all the previously thrown exceptions are ignored & the corresponding o/p i.e "peace" is printed.

Not always this happen. If a unchecked exception is thrown in try block, that will be printed after executing the finally block.

Regards,
Narendranath

[Chris Allen]

Originally posted by Naren Chivukula:
Hi,
Not always this happen. If a unchecked exception is thrown in try block, that will be printed after executing the finally block.

Hmmm, I don't think this is true. Consider the following code below:

public class Test2 {
  static String raid () {
    try{
    throw new RuntimeException();
    } catch ( Exception e ) {
        int i = 10/0;
        return " Error " ;
    } finally{
        return " Peace " ;
    }
} 
  public static void main ( String args [ ] ) {
    System.out.println(raid()); 
  }
} 

The output is "Peace" (without the quotes) and the RunTimeException error is not displayed.

[Raghuveer Kumarakrishnan]

Swathi got it right,thats the correct explanation

RunTimeException is generated , we are already in catch so execution goes to finally ,where "Peace" gets returned.

[Naren Chivukula]

Hi,

Hmmm, I don't think this is true. Consider the following code below:

As you are catching the exception in the catch block, you can't get the exception thrown after finally block executes. If you don't use catch block over there, then certainly system throws RuntimeException after executing finally block code.

Regards,
Narendranath

[Chris Allen]

Nare,

You stated the following:

If a unchecked exception is thrown in try block, that will be printed after executing the finally block.

All I wanted to indicate was that a Runtime exception will NOT ALWAYS be printed (as it was caught in a try block). You are correct that it will display if not caught by a catch block.

Perhaps we could agree that if you modified the statement to be "If an unchecked exception is thrown in a try block that is not caught by an exception clause, the runtime exception will be printed after executing the finally block".

[Ernest Friedman-Hill]

Originally posted by Chris Allen:
You are correct that it will display if not caught by a catch block.

No, actually, he's not correct under any circumstances. Returning from a method inside a finally block will "cancel" all pending exceptions, caught or uncaught, whether there's a matching catch block or even no catch block at all. Try this:

public class Silent {
     public static void main(String[] argv) {
try {
    String s = null;
    System.out.println(s.length());
} finally {
    return;
}
    }
}

Running this program produces no output.

[Naren Chivukula]

Perhaps we could agree that if you modified the statement to be "If an unchecked exception is thrown in a try block that is not caught by an exception clause, the runtime exception will be printed after executing the finally block".

A java files never goes without catching unchecked exception. Compiler will not compile the java file unless you catch that unchecked exception!

No, actually, he's not correct under any circumstances. Returning from a method inside a finally block will "cancel" all pending exceptions, caught or uncaught, whether there's a matching catch block or even no catch block at all.

I too agree. If we have simple SOP statement in finally block, then the
RuntimeException thrown in try block will be printed on the console. I need to elaborately study on this...

Narendranath
-- Always try to write right statements