try finally without a catch:

[Vishwanath Krishnamurthi]

Hi guys,

I thought try block immediately followed by a finally block wouldn't mean that the Exception is handled and that it should be declared. And I had also tried out some programs and results suggeated the same.

But here in this code, I thought the test2() method should declare that it throws the exception. Well, it doesn't. And it compiles just fine...

Can anyone please clarify...

Src: javabeat

 public class Ques04 
{
  public static void main(String[] args) {
  System.out.println(test1());
}
 

static int test1()
{
   if (test2() == -1)
      {
       try{
                throw new Exception("test1");
            }
 
        catch(Exception e){
              return 5;
           }
        finally{
            return 3;
        }
      }
 
 else
    {
       return 6;
     }
}
 

 
static int test2()
  {
    if (true)
     {
                try{
                       throw new Exception("test2");
                      } 
               finally
                    {
                        return -1;
                    }
    }
   else
     {
       return 9;
     }
 
  }
}   

OPTIONS:
1. The program won't compile because of compilation errors.
2. The program will throw Exception at run-time.
3. The program will print 6.
4. The program will output 9.
5. The program will display 3.

ANS ption 5

[Deepak Jain]

Yes the answer is 3. What is your confusion.
Am feeling
Reaching 300
[ January 17, 2008: Message edited by: Deepak Jain ]

[Raghavan Muthu]

Hi Vishwanath Murthi,


Yes the answer is correct. 3 is what getting returned and displayed.

I thought try block immediately followed by a finally block wouldn't mean that the Exception is handled and that it should be declared. And I had also tried out some programs and results suggeated the same.

But here in this code, I thought the test2() method should declare that it throws the exception. Well, it doesn't. And it compiles just fine...

Here you have mistaken. The point is that,

If you handle the exception (using try/catch blocks), you do NOT need to declare the throws statement. That means, you intimate that you yourself handle the exceptions in the method.

on the other hand, if you don't handle the exception but simply throw an exception, you need to declare that in the method signature using throws statement.

As such the test() method handles the exception it its try/catch block, there is NO need for it to have throws clause. So the entire program compiles and runs just fine.

Hope you are clear with the flow of execution

[Pranob Samani]

The answer will be three as the finally block is executed any ways.

it doesnot make any difference whether it goes to that loop or not

Hope that helps!

[Raghavan Muthu]

You may please go through this code for your further explanation

public class WithAndWithOutThrowsDemo {
    
    /** Creates a new instance of WithAndWithOutThrowsDemo */
    public WithAndWithOutThrowsDemo() {
    }
    
    public void methodThrowsException() throws Exception {
        throw new Exception();
    }
    
    public void methodHandlesException() {
        try{
            throw new Exception();
        }catch(Exception exception){
            System.err.println("I am handling the exception myself. NO NEED to declare throws  :) ");
        }
    }
    
    public static void main(String[] args) {
        WithAndWithOutThrowsDemo demoObj = new WithAndWithOutThrowsDemo();
        
        /*
         * Here you need to follow any of the two rules since the method you are going to call
         * "methodThrowsException" is having a 'throws' clause in its signature.
         *    (i) you should embed your call in a try/catch block
         *    (ii)you should add a 'throws' clause to the method that calls your target method.
         *            Here we call this method from our main() method. 
         *
         *  We will follow option1.
         */
        try{
            demoObj.methodThrowsException();
        }catch(Exception exception) {
            System.err.println("Caught the exception thrown by methodThrowsException()");
        }
        
        //No need to have any try/catch here since it IS handled in the method itself!
        demoObj.methodHandlesException();
    }    
}

Hope this helps!

[Vishwanath Krishnamurthi]

Hi guys,

The rule says "catch or declare" right...
My confusion lies here:

When we use a try block followed by a finally block without any catch block:
any exception if any is not actually caught and just passed to the invoking method..rite?

So we haven't caught the exception. So we gotto declare the exception atleast, right?

And the code below,

  class Hand
  {
     public void aMethod() //LLL
        {
           try
               {
                   throw new Exception("Heee");
                }
           finally
                {
                    System.out.println("One");
                 }
           }
     }
 

                    
 

class Handle
  {
     public static void main(String[] args)throws Exception
        {
              new Hand().aMethod();
         }
 
  }
 
  

gives an error saying that there should be a throws clause there.... (in LLL)

Well, so try-finally-(no-catch) block requires a throws declaration rite..?

The test2() method in the prev code has a try-finally-(no-catch) block and does not have a throws declaration???

Thats where I am getting confused.. Why isn't this code givin a compiler-error...


(I can see that o/p must be three if it runs successfully... and it does)

[Vishwanath Krishnamurthi]

am very sorry... in the first post I meant to say

I thought try block immediately followed by a finally block, without any catch block at all, wouldn't mean that the Exception is handled and that it should be declared.

but typed

I thought try block immediately followed by a finally block wouldn't mean that the Exception is handled and that it should be declared.

[Raghavan Muthu]

Originally posted by Vishwanath Murthi:
...
When we use a try block followed by a finally block without any catch block:
any exception if any is not actually caught and just passed to the invoking method..rite?

So we haven't caught the exception. So we gotto declare the exception atleast, right?

Yes, but it does have a "return" statement.

Try the code with "try-finally with return" and "try-finally without return". for the second one, you need to have a throws clause!

That's the difference

[Vishwanath Krishnamurthi]

Hi,

Thanks a lot.

[Alpesh Vesuwala]

Hi friends,

Raghavan's point is right and I want to elaborate that,

1) If method returns nothing and if you throw an Exception in a try block that does not handle by the catch block and not even handle by the caller then compiler will raise an error stating unhandled exception.

2) If method returns some value and if you throw an Exception in a try block that does not handle by the catch block, you do not return any value in your finally block and not even handle by the caller then compiler will raise an error stating unhandled exception.

3) If method returns some value and if you throw an Exception in a try block that does not handle by the catch block and not even handle by the caller but this time you return some value from your finally block then compiler will acept the things knowing that error occurs or not finally block is going to execute anyhow and will return some value, so no point of handling the error and will result in the value return by the fianlly block.


hope it clears now.

Alpesh

[Raghavan Muthu]

Howdy Alpesh Vesuwala ,

Welcome to JavaRanch

[Raghavan Muthu]

Originally posted by Alpesh Vesuwala:

....3) If method returns some value and if you throw an Exception in a try block that does not handle by the catch block and not even handle by the caller but this time you return some value from your finally block then compiler will acept the things knowing that error occurs or not finally block is going to execute anyhow and will return some value, so no point of handling the error and will result in the value return by the fianlly block.

That is a nice explanation Alpesh!

[Vishwanath Krishnamurthi]

Hi,

you return some value from your finally block then compiler will acept the things knowing that error occurs or not finally block is going to execute anyhow and will return some value, so no point of handling the error and will result in the value return by the fianlly block.

Thanks a lot for the clarification..
So I see that a finally block can also be used to return a default-value in case an exception occurs...

I tried this..

 class Hand
  {
     public int aMethod() //LLL
        {
           try
               {
                   if(true)
                   throw new Exception("Heee");
                   return 3;
                }
           finally
                {
                    System.out.println("One");
                    return 4;
                 }
           }
     }
 
class Handle
  {
     public static void main(String[] args)throws Exception
        {
             System.out.println(new Hand().aMethod());
         }
 
  }   

Thanks...

[Raghavan Muthu]

That's great viswanathan