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problem with re-throwing exception

2 replies on 1 page. Most recent reply: Apr 18, 2007 11:19 PM by fly man

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MIrko Panagrosso

Posts: 1
Nickname: microbo
Registered: Apr, 2007

problem with re-throwing exception

Posted: Apr 4, 2007 5:58 AM

Hello,
would you be so gentle to explain us something.
We had a concept problem while studing "thinking in java". We are not able to realize about the rethrowing of a catched exception; particularly we don't understand the following sentence: the Rethrowing an exception causes it to go to the exception handlers in the next-higher context. reading the code we wasn't able to understand who is the next-higher context (number 17):

//: c09:Rethrowing.java
// Demonstrating fillInStackTrace()
import com.bruceeckel.simpletest.*;

public class Rethrowing {
private static Test monitor = new Test();
public static void f() throws Exception {
System.out.println("originating the exception in f()");
throw new Exception("thrown from f()");
}
public static void g() throws Throwable {
try {
f();
} catch(Exception e) {
System.err.println("Inside g(),e.printStackTrace()");
e.printStackTrace();
throw e; // 17 HERE THE EXCEPTION IS RE-THROWED BUT WE DON'T UNDERSTAND WHO CATCHES IT
// throw e.fillInStackTrace(); // 18
}
}
public static void
main(String[] args) throws Throwable {
try {
g();
} catch(Exception e) {
System.err.println(
"Caught in main, e.printStackTrace()");
e.printStackTrace();
}
monitor.expect(new String[] {
"originating the exception in f()",
"Inside g(),e.printStackTrace()",
"java.lang.Exception: thrown from f()",
"%% \tat Rethrowing.f(.*?)",
"%% \tat Rethrowing.g(.*?)",
"%% \tat Rethrowing.main(.*?)",
"Caught in main, e.printStackTrace()",
"java.lang.Exception: thrown from f()",
"%% \tat Rethrowing.f(.*?)",
"%% \tat Rethrowing.g(.*?)",
"%% \tat Rethrowing.main(.*?)"
});
}
} ///:~

thanks

Vincent O'Sullivan

Posts: 724
Nickname: vincent
Registered: Nov, 2002

Re: problem with re-throwing exception

Posted: Apr 4, 2007 6:30 AM

> ...we were not able to understand who
> is the next-higher context (number 17):

The 'next higher context' is the method that calls the method that throws the Exception. In your example it is the 'main' method. In other circumstances it could be a method in another class that calls g(). The point is that method g() does not know what method is calling it.

fly man

Posts: 1
Nickname: flyman
Registered: Apr, 2007

Re: problem with re-throwing exception

Posted: Apr 18, 2007 11:19 PM

in my opinion ,the next-higher context is the invoker.

'public static void f() throws Exception'

just do catch the Exception

'throw new Exception("thrown from f()");'

tell the invoker must deal with this Exception

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