understanding try-catch block?

[Sonali Sehgal]

can we write return statement in try catch or finally block.
supose we write return 0 in try catch or finally. is it right or wrong?

[Ankit Garg]

Yes you can return a value in try, catch and finally block. You just need to remember that finally block will always be executed...

[Lucas Smith]

It is OK to write return in try{}catch{}finally{} block. We can write return; (when a function is declared as void) or return typeValue; (when a function is declared as not void).

 public int exceptionTest() {  
   try {  
     throw new Exception();  
   }  
   catch (Exception e) {  
     return 1;  
   }  
   finally {  
     return 2;  
   }  
 }  

The returned value will be 2.

public class ExceptionTest {
	public int returnValue(int x) {
		System.out.println("Returning value: " + x);
		return x;
	}
	
	public int testException() {
		try {
			throw new Exception();
		}
		catch (Exception e) {
			return returnValue(1);
		}
		finally {
			return returnValue(2);
		}
	}
	
	public static void main(String args[]) {
		System.out.println("Returned value: " + new ExceptionTest().testException());
	}
}

Result:
Returning value: 1
Returning value: 2
Returned value: 2



Very interesting thing happens when we write return inside finally block:

public int testException() {
	try {
		throw new Exception();
	}
	finally {
		return 0;
	}
}

The above code is OK! The exception is NOT handled, but it is CONSUMED!

[Lucas Smith]

Ankit Garg wrote:Yes you can return a value in try, catch and finally block. You just need to remember that finally block will always be executed...

Not at all. System.exit(0) will cause that finally will not be executed and internal error/exception of JVM can cause the same

[karthikeyan Chockalingam]

And also finally will suppress any return in catch block.. For instance the below code will print 5.

   
public class TestMain {

    public static void main(String[] args) throws Exception {

        System.out.println(TestMain.doStuff());

    }

    private static int doStuff() {
        try {
            throw new Exception("exception");
        } catch (Exception e) {
            return 2;
        } finally {
            return 5;
        }

    }
}
 

[Sonali Sehgal]

Thanks a lot to all of you.I have understood the concept.

[Ankit Garg]

Lukas Smith wrote:

Ankit Garg wrote:Yes you can return a value in try, catch and finally block. You just need to remember that finally block will always be executed...

Not at all. System.exit(0) will cause that finally will not be executed and internal error/exception of JVM can cause the same

But you don't need to worry about that in SCJP ...

[Lucas Smith]

Shanmuga Priya wrote:And also finally will suppress any return in catch block.. For instance the below code will print 5.

   
public class TestMain {

    public static void main(String[] args) throws Exception {

        System.out.println(TestMain.doStuff());

    }

    private static int doStuff() {
        try {
            throw new Exception("exception");
        } catch (Exception e) {
            return 2;
        } finally {
            return 5;
        }

    }
}
 

I have just figured this out

Sonali - you are welcomed!

[Lucas Smith]

Ankit Garg wrote:

Lukas Smith wrote:

Ankit Garg wrote:Yes you can return a value in try, catch and finally block. You just need to remember that finally block will always be executed...

Not at all. System.exit(0) will cause that finally will not be executed and internal error/exception of JVM can cause the same

But you don't need to worry about that in SCJP ...

System.exit(0) can be tested during SCJP. Stay tuned.

[Ankit Garg]

I was only trying to say that I've never seen a question combining try catch block and System.exit. So generally you can say that finally block is sure to be executed...

PS: Bert can confirm on that more...

[Lucas Smith]

Ankit Garg wrote:I was only trying to say that I've never seen a question combining try catch block and System.exit. So generally you can say that finally block is sure to be executed...

PS: Bert can confirm on that more...

"Never say never..." - from the song

Just a joke

[Rashmi Liyan]

Lukas Smith wrote:It is OK to write return in try{}catch{}finally{} block. We can write return; (when a function is declared as void) or return typeValue; (when a function is declared as not void).

Hi Lukas,
can you exlain this little bit. I didn't get it.

Rashmi.

[Muhammad Khojaye]

Lukas Smith wrote:

Ankit Garg wrote:

Lukas Smith wrote:

Ankit Garg wrote:Yes you can return a value in try, catch and finally block. You just need to remember that finally block will always be executed...

Not at all. System.exit(0) will cause that finally will not be executed and internal error/exception of JVM can cause the same

But you don't need to worry about that in SCJP ...

System.exit(0) can be tested during SCJP. Stay tuned.

You usually put in a finally block the code that must happen no matter how the try block is exited. So thinking of System.exit(0) or JVM internal error/exception is not important for me when i write finally block.

[Vinay Dinakar]

 
public class VariableTest {

    int test(){
        
        try{
       
            System.exit(0);
           // return 1;
        }catch(Exception e){
            e.printStackTrace();
            return 1;
        }
        finally{
        
            System.out.println("hey");
            return 1;
        }
    }
}

System.exit(0) makes control to return without executing finally block (Which is having return statement). So now there is no return value, why doesn't compiler throws an error ?

[Jehaan Butt]

public class VariableTest {  
  
    int test(){  
          
        try{  
         
            System.exit(0);  
           // return 1;  
        }catch(Exception e){  
            e.printStackTrace();  
            return 1;  
        }  
        finally{  
          
            System.out.println("hey");  
            return 1;  
        }  
    }  
}  

System.exit(0) makes control to return without executing finally block (Which is having return statement). So now there is no return value, why doesn't compiler throws an error ?

Well, here your try block is not throwing an exception, due to which there will be no internal JVM error. The System.exit(0) merely exits the program, and that does not cause any error.

   public class VariableTest {  
  
    int test(){  
          
        try{  
         
			throw new Exception();
             
           // return 1;  
        }catch(Exception e){  
            e.printStackTrace();  
           System.exit(0); 
			return 1;  
        }  
        finally{  
          
            System.out.println("hey");  
            return 1;  
        }  
    }  
	public static void main(String[]args)
	{
		VariableTest v=new VariableTest();
		v.test();
	}
}   

This version of code does give an internal JVM error, because there is an internal exception lurking around the JVm which has not been handled.

[Vinay Dinakar]

Ok. Thats fine. But my question is , compiler sees that test method return type is "int". But there is no "return" statement gets called here. So Why compiler doesn't say like "return statement is missing" ?

[Jehaan Butt]

Ok. Thats fine. But my question is , compiler sees that test method return type is "int". But there is no "return" statement gets called here. So Why compiler doesn't say like "return statement is missing" ?

My guess (and it is only a guess) is that the compiler doesn't realise that either of the two return calls will not be reached. It sees that the System.exit(0) call is reached and is happy, because when I tried throwing an exception before the call it complained. It does not actually work out the complete code logic and since both the catch and finally have return statements, it feels that there is no problem.