exception handling

[anushree ari]

i came through this question in dan's topic exam,
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 (Level1Exception e) { d++;}
catch (Exception e) {f++;}
finally {g++;}
System.out.print(a+","+b+","+c+","+d+","+f+","+g);
}
}
th/
thxe ans is 0 1 1 0 0 1,
how

[sun par]

i came through this question in dan's topic exam,
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 (Level1Exception e) { d++;}
catch (Exception e) {f++;}
finally {g++;}
System.out.print(a+","+b+","+c+","+d+","+f+","+g);
}
}
th/
thxe ans is 0 1 1 0 0 1,
how

Level3Exception is a sub class of Level2Exception.So the inner catch block of Level2Exception is matched.. b is incremented... finally block c is incremented.. Since the exception has been handled the outer catch blocks are not executed.. the outer finally block is executed and g is incremented..
So u get a=0 b=1 c=1 d=0 f=0 g=1
Hope this helps

[anushree ari]

iam sorry ididn't get,
since level3 is subclass level2 but levels2 is super class exception,
i think iam confusing the exception hiriachy,
pls anybody correct me,
thx

[sun par]

when u have nested try blocks and an exception is caught in the inner try block, first the inner catch block is compared to see if there is an match.. We can consider that there is a match if there is an exception of that class or a super class of that class... If it is handled then the exceptions do not get propogated to the outer catch statements.

[Alfred Kemety]

ok, simple and easy:
If xException extends yException, then yException is a super class of xException.
SO what catch yException, catch xException as well. what catch yException can catch ALL its subclasses and their subclasses.

try {
    throw new xException();
}
catch (yException ye) {   //this catch xException as well
System.out.println("xException is caught");
}

got the picture?
one more important thing about try-catch-finally construct.
A catch that follows another catch that catchs a super class exception can NOT catch a subclass exception. hmmmm not clear?
look at this code also assuming xException extends yException:

try {
    throw new xException();
}
catch (yException ye) {   //mark 1
System.out.println("xException is caught");
}
catch (xException xe) {   //mark 2
// whatever
}

previous code generates a compile time error, type of exections at mark 1 and mark 2 needs to replace each other.
HTH

[anushree ari]

thx alfred and sunita,
i hope i got enough,
thx