Exceptions

[Mubeen Shaik]

Hi All,

This code is from Dan Chisholm mock exam. I have changed the original question and compiled this. It is giving the following error message.
Please explain this error.

  
 
Purple.java:19: exception Level3Exception is never thrown in body of corresponding try statement
    catch (Level3Exception e) { d++;}
    ^
1 error
 

  
 
class Level1Exception extends Exception {}
class Level2Exception extends Level1Exception {}
class Level3Exception extends Level2Exception {}
class Purple {
  public static void main(String args[]) {
    int a,b,c,d,f,g,x;
    a = b = c = d = f = g = 0;
    x = 1;
    try {
      try {
        switch (x) {
          case 1: throw new Level1Exception();
          case 2: throw new Level2Exception();
          case 3: throw new Level3Exception();
      } a++; }
      catch (Level1Exception e) {b++;}
      finally {c++;}
    }
    catch (Level3Exception e) { d++;}
    catch (Exception e) {f++;}
    finally {g++;}
    System.out.print(a+","+b+","+c+","+d+","+f+","+g);
}}
 

Thanks in advance,
Mubeen

[Dave Wingate]

The exception is a result of the fact that e1 is the parent class of e3. The first catch statement (e1) will catch all e3 exceptions thrown. The compiler is smart enough to know that any e3 exception thrown will never make it outside of the e1 block.

Try switching the order of the catch blocks and it should compile -- i.e. catch e3 and then later catch e1.

[Mubeen Shaik]

Thanks for the explanation Dave. It woks as you have said.

Now i am more confused with the following code.

Here Level3Exception is child of Level2Exception.(Correct?). This code compiles and runs. I am confused with this.

My Question what is the difference between this code and previous one?.

=====================

 
class Level1Exception extends Exception {}
class Level2Exception extends Level1Exception {}
class Level3Exception extends Level2Exception {}
 
class Purple {
  public static void main(String args[]) {
    int a,b,c,d,f,g,x;
    a = b = c = d = f = g = 0;
    x = 3;
    try {
      try {
        switch (x) {
          case 1: throw new Level1Exception();
          case 2: throw new Level2Exception();
          case 3: throw new Level3Exception();
      } a++; }
      catch (Level2Exception e) {b++;}  
      finally {c++;}
    }
    catch (Level3Exception e) { d++;}
    catch (Exception e) {f++;}
    finally {g++;}
    System.out.print(a+","+b+","+c+","+d+","+f+","+g);
}}
 
 

Thanks in advance
Mubeen.

[Dave Wingate]

When working these types of problems, it can be helpful to drwaw pictures. e2 and e3 are peers in this case:

        Exception
            |
           e1
            |
         --------
         |      |
         e2     e3

Here e3 doe not inherit from e2.
[ February 14, 2005: Message edited by: Dave Winn ]

[Mubeen Shaik]

Because of "extends", i thought it will be like this.

Now how e2 and e3 are at the same level? Please explain.




Exception
-----------
e1
----------
e2
---------
e3


Thanks in advance,
Mubeen.

[Renaud Richardet]

Hi Mubeen
I have posted an answer to this forum, where you also posted this question. please don't post your question twice.
Renaud

[Renaud Richardet]

Hi Dave

I completely agree with your first post. However, i don't get it when you say:

Here e3 doe not inherit from e2.

on your second post. I believe the heritage diagram from Mubeen is right.

Cheers, Renaud