Interface and exceptions

[Hans Beck�rus]

I read the following
A legal nonabstract implementing class has the following properties:
...
- It must not declare any new checked exceptions for an implementation method.
- It must not declare any checked exceptions that are broader than the exceptions declared in the interface method.
...

I have some problem understanding how you could fulfil the first but fail to fulfil the second?

Anyone that could explain (maybe with a simple code example) how these rules correlate?

[Gowher Naik]

import java.io.*;
interface MyInterface{
void print()throws IOException;
void printAgain() throws IOException;
}
public class Test implements MyInterface{
public void print()throws IOException{//line 7
//at line 7 change IOException with Exception
}
public void printAgain()throws IOException{//line 10
 //at line 10 change IOException with IOException,Exception
}
}

Check comments in above code.
Make changes according comments and see the result.
Try to understand compiler error messages.

[wise owen]

    
class AE extends Exception {
}
 
class BE extends Exception {
}
 
class AEa extends AE {
}
 
class BEa extends BE {
}
 
interface MyInterface {
void method1() throws AE;
void method2() throws BEa;
}
 
class MyClass implements MyInterface {
 
public void method1() throws AE, BE { //compile-time error
}
 
public void method2() throws BE { //compile-time error
}

}

[ August 30, 2006: Message edited by: wise owen ]

[Hans Beck�rus]

Thanks guys. That did the trick.
Now it is all crystal clear!

[joy peter]

Non abstract implementation class can throw broader exceptions but not new surprise exceptions that are not in super class.