Exceptions/Catch an exception thrown in a nested call

Exceptions/Catch an exception thrown in a nested call
You are encouraged to solve this task according to the task description, using any language you may know.

Show how to create a user-defined exception and show how to catch an exception raised from several nested calls away.

1. Create two user-defined exceptions, U0 and U1.
2. Have function foo call function bar which then calls function baz.
3. Arrange for function baz to raise, or throw exception U0 on its first call, then exception U1 on its second.
4. Function foo should catch only exception U0, not U1.

Show/describe what happens when the program is run.

Ada

<lang ada>with Ada.Text_Io; use Ada.Text_Io;

procedure Exceptions_From_Nested_Calls is

  U0 : exception;
  U1 : exception;
  Baz_Count : Natural := 0;
  procedure Baz is
  begin
     Baz_Count := Baz_Count + 1;
     if Baz_Count = 1 then
        raise U0;
     else
        raise U1;
     end if;
  end Baz;
  procedure Bar is
  begin
     Baz;
  end Bar;
  procedure Foo is
  begin
     Bar;
  exception
     when U0 =>
        Put_Line("Procedure Foo caught exception U0");
  end Foo;

begin

  for I in 1..2 loop
     Foo;
  end loop;

end Exceptions_From_Nested_Calls;</lang> Sample output:

Procedure Foo caught exception U0

raised EXCEPTIONS_FROM_NESTED_CALLS.U1 : exceptions_from_nested_calls.adb:13

D

First exception will be caught and message will be displayed, second will be caught by default exception handler.

<lang D> module test;

import tango.io.Stdout;

class U0 : Exception { this() { super("U0 error message"); } } class U1 : Exception { this() { super("U1 error message"); } }

void foo() {

   for (int i = 0; i < 2; i++)
   {   
       try {
           bar(i);
       } catch(U0 e) {
           Stdout ("Exception U0 caught").newline;
       }
   }

}

void bar(int i) { baz(i); } void baz(int i) {

   if (!i) throw new U0;
   else throw new U1;

}

void main() { foo(); } </lang>

Result:

Exception U0 caught
test.U1: U1 error message

If you have tango stack-trace, stack-trace will be print after second message.

Java

Methods that may throw an exception (or that call a method that may throw an exception that it does not catch) must explicitly declare that they can throw such an exception (or a superclass thereof), unless they are unchecked exceptions (subclasses of RuntimeException or Error): <lang java>class U0 extends Exception { } class U1 extends Exception { }

public class ExceptionsTest {

   public static void foo() throws U1 {
       for (int i = 0; i <= 1; i++) {
           try {
               bar(i);
           } catch (U0 e) {
               System.out.println("Function foo caught exception U0");
           }
       }
   }

   public static void bar(int i) throws U0, U1 {
       baz(i); // Nest those calls
   }

   public static void baz(int i) throws U0, U1 {
       if (i == 0)
           throw new U0();
       else
           throw new U1();
   }

   public static void main(String[] args) throws U1 {
       foo();
   }

}</lang> Sample output:

Function foo caught exception U0
Exception in thread "main" U1
	at ExceptionsTest.baz(ExceptionsTest.java:23)
	at ExceptionsTest.bar(ExceptionsTest.java:16)
	at ExceptionsTest.foo(ExceptionsTest.java:8)
	at ExceptionsTest.main(ExceptionsTest.java:27)

The first line of the output is generated from catching the U0 exception in function foo.

Uncaught exceptions give information showing where the exception originated through the nested function calls together with the name of the uncaught exception, (U1) to stderr, then quit the running program.

OCaml

<lang ocaml>exception U0 exception U1

let baz i =

 raise (if i = 0 then U0 else U1)

let bar i = baz i (* Nest those calls *)

let foo () =

 for i = 0 to 1 do
   try
     bar i
   with U0 ->
     print_endline "Function foo caught exception U0"
 done

let () = foo ()</lang> Sample output:

Function foo caught exception U0
Exception: U1.

Python

There is no extra syntax to add to functions and/or methods such as bar, to say what exceptions they may raise or pass through them: <lang python>class U0(Exception): pass class U1(Exception): pass

def foo():

   for i in range(2):
       try:
           bar(i)
       except U0:
           print "Function foo caught exception U0"

def bar(i):

   baz(i) # Nest those calls

def baz(i):

   raise U1 if i else U0

foo()</lang> Sample output:

Function foo caught exception U0

Traceback (most recent call last):
  File "C:/Paddy3118/Exceptions_Through_Nested_Calls.py", line 17, in <module>
    foo()
  File "C:/Paddy3118/Exceptions_Through_Nested_Calls.py", line 7, in foo
    bar(i)
  File "C:/Paddy3118/Exceptions_Through_Nested_Calls.py", line 12, in bar
    baz(i) # Nest those calls
  File "C:/Paddy3118/Exceptions_Through_Nested_Calls.py", line 15, in baz
    raise U1 if i else U0
U1

The first line of the output is generated from catching the U0 exception in function foo.

Uncaught exceptions give information showing where the exception originated through the nested function calls together with the name of the uncaught exception, (U1) to stderr, then quit the running program.