Exception thrown inside catch block - will it be caught again

Question

This may seem like a programming 101 question and I had thought I knew the answer but now find myself needing to double check  In this piece of code below  will the exception thrown in the first catch block then be caught by the general Exception catch block below   try        Do something   catch IOException e      throw new ApplicationException  Problem connecting to server      catch Exception e         Will the ApplicationException be caught here      I always thought the answer would be no  but now I have some odd behaviour that could be caused by this  The answer is probably the same for most languages but I m working in Java

User · Answer

If you want to throw an exception from the catch block you must inform your method/class/etc. that it needs to throw said exception. Like so:

public void doStuff() throws MyException {
    try {
        //Stuff
    } catch(StuffException e) {
        throw new MyException();
    }
}

And now your compiler will not yell at you :)

User · Answer

The Java Language Specification says in section 14 19 1   If execution of the try block completes abruptly because of a throw of a value V  then there is a choice   If the run-time type of V is assignable to the Parameter of any catch clause of the try statement  then the first  leftmost  such catch clause is selected  The value V is assigned to the parameter of the selected catch clause  and the Block of that catch clause is executed  If that block completes normally  then the try statement completes normally  if that block completes abruptly for any reason  then the try statement completes abruptly for the same reason    Reference  http   java sun com docs books jls second edition html statements doc html 24134 In other words  the first enclosing catch that can handle the exception does  and if an exception is thrown out of that catch  that s not in the scope of any other catch for the original try  so they will not try to handle it  One related and confusing thing to know is that in a try- catch -finally structure  a finally block may throw an exception and if so  any exception thrown by the try or catch block is lost   That can be confusing the first time you see it

User · Answer

As said above    I would add that if you have trouble seeing what is going on  if you can t reproduce the issue in the debugger  you can add a trace before re-throwing the new exception  with the good old System out println at worse  with a good log system like log4j otherwise

User · Answer

No -- As Chris Jester-Young said  it will be thrown up to the next try-catch in the hierarchy

User · Answer

No  It s very easy to check   public class Catch       public static void main String   args            try               throw new java io IOException              catch  java io IOException exc                System err println  In catch IOException    exc getClass                 throw new RuntimeException              catch  Exception exc                System err println  In catch Exception    exc getClass               finally               System err println  In finally                        Should print    In catch IOException  class java io IOException In finally Exception in thread  main  java lang RuntimeException         at Catch main Catch java 8   Technically that could have been a compiler bug  implementation dependent  unspecified behaviour  or something  However  the JLS is pretty well nailed down and the compilers are good enough for this sort of simple thing  generics corner case may be a different matter    Also note  if you swap around the two catch blocks  it wont compile  The second catch would be completely unreachable   Note the finally block always runs even if a catch block is executed  other than silly cases  such as infinite loops  attaching through the tools interface and killing the thread  rewriting bytecode  etc

User · Answer

No  since the catches all refer to the same try block  so throwing from within a catch block would be caught by an enclosing try block  probably in the method that called this one

User · Answer

No  since the new throw is not in the try block directly

User · Answer

Old post but  e  variable must be unique   try        Do something   catch IOException ioE      throw new ApplicationException  Problem connecting to server      catch Exception e         Will the ApplicationException be caught here

User · Answer

It won t be caught by the second catch block  Each Exception is caught only when inside a try block  You can nest tries though  not that it s a good idea generally    try       doSomething      catch  IOException       try          doSomething         catch  IOException e           throw new ApplicationException  Failed twice at doSomething           e toString                      catch  Exception e

[java] Exception thrown inside catch block - will it be caught again?

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