CODEWITHSUNDEEP
java
user3248346
user3248346

Reputation:

Unreachable statement explanation required

I'm preparing for OCA Java exam and got this question wrong. I can't see why the return statement is unreachable. My thinking is that even if an exception is thrown it will be caught, the statement in the finally block executed and then the return statement is executed, or is it the case that the thread does not execute the return statement if an exception is thrown? More generally, can somebody explain the rules of what happens in the case of an exception being fired and in which cases statements after the finally block are executed or not. For some questions I am getting this correct and for others I am not so I am not clear on the exact compiler rules here.

public float parseFloat(String s){
   float f = 0.0f;
   try{
      f = Float.valueOf(s).floatValue();
      return f ;
   }
   catch(NumberFormatException nfe){
      System.out.println("Invalid input " + s);
      f = Float.NaN ;
      return f;
   }
   finally { System.out.println("finally");  }
   return f ;
}

Upvotes: 0

Views: 216

Answers (2)

dube
dube

Reputation: 5039

  1. If an exception occurs, the code drops out immediately
  2. It then checks, if there is a matching catch statement and if it does, it's code then runs
  3. regardless of what happens inside of the try or the catch blocks, the finally part will always run.
  4. if the catch block did not make a return OR throw an exception itself, the code after the try/catch/finally continues to run.
  5. this is not possible in your code, because in the success case your try block does return and in the fail-case your catch block returns.

so there might be a theoretical case, where your code would make sense: If the code inside the try{} block would throw any other exception besides NumberFormatException. This is only possible, if it is an unchecked exception (the ones you are not required to catch). The compiler cannot know or check this, therefore such code is not allowed unless you write a second catch block for it. (if you are confused now: forget what I said, it's not important for your task)

here is a sample of such a case:

public float parseFloat(String s){
   float f = 0.0f;
   try{
      SomeOtherClass.doStuffWhichFailsWithRuntimeException();
      return f;
   }
   catch(NumberFormatException nfe){
       // will not run, because the thrown exception is not of type NumberFormatException
   }catch(Exception e){
       // any other failure besides NumberFormatException
       // considered bad practice: If you do not know what fails, do not try to recover from it, it's most likely very bad.
      return f;
   }
   finally { 
      // this will run after the catch block was run
      System.out.println("finally");  
   }

   // theoretically reachable, but compiler does not allow it because he cannot check it.
   //return f ;
}

Upvotes: 3

Stelium
Stelium

Reputation: 1367

If an exception is occured then catch block runs, f is returned and finally block runs next. The last

return f;

will never be reached.

Upvotes: 1

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