Exceptions

This task is to give an example of an exception handling routine and to "throw" a new exception.

AppleScript

try

try
    set num to 1 / 0
    --do something that might throw an error
end try

try-on error

try
    set num to 1 / 0
    --do something that might throw an error
on error errMess number errNum
    --errMess and number errNum are optional
    display alert "Error # " & errNum & return & errMess
end try

throw

error "Error message." number 2000

C++

C++ has no finally construct. Instead you can do this in the destructor of an object on the stack, which will be called if an exception is thrown.

try-catch

 struct MyException
 {
   // data with info about exception
 };

 void foo()
 {
   throw MyException();
 }

 void call_foo()
 {
   try {
     foo();
   }
   catch (MyException &exc)
   {
     // handle exceptions of type MyException and derived
   }
   catch (...)
   {
     // handle any type of exception not handled by above catches
   }
 }

C#

Compiler: MSVS 2005

 public class MyException : Exception
 {
   // data with info about exception
 };

 void foo()
 {
   throw MyException();
 }

 void call_foo()
 {
   try {
     foo();
   }
   catch (MyException e)
   {
     // handle exceptions of type MyException and derived
   }
   catch
   {
     // handle any type of exception not handled by above catches
   }
 } 

Java

Defining exceptions

  //Checked exception
  public class MyException extends Exception {
     //Put specific info in here
  }

  //Unchecked exception
  public class MyRuntimeException extends RuntimeException {}

Throw exceptions

  public void fooChecked() throws MyException {
     throw new MyException();
  }

  public void fooUnchecked() {
     throw new MyRuntimeException();
  }

Catching exceptions

  try {
     fooChecked();
  }
  catch(MyException exc) {
     //Catch only your specified type of exception
  }
  catch(Exception exc) {
     //Catch any non-system error exception
  }
  catch(Throwable exc) {
     //Catch everything including system errors (not recommended)
  }
  finally {
     //This code is always executed after exiting the try block
  }

Perl

# throw an exception
die "Danger, danger, Will Robinson!";

# catch an exception and show it
eval {
    die "this could go wrong mightily";
};
print $@ if $@;

# rethrow
die $@;

See http://perldoc.perl.org/perlvar.html#%24EVAL_ERROR for the meaning of the special variable $@. See http://search.cpan.org/dist/Error for an advanced, object based exception handling.

Python

try-except-finally-else

Interpreter: Python 2.5

Before Python 2.5 it was not possible to use finally and except together.

try:
   foo()
except TypeError:
   bar()
finally:
   baz()
else:
   # no exception occurred
   quux()