Trying to understand when to use 'finally' clause

[Smith Li]

I'm trying to understand the use of finally clause. I have these lines of codes below and it will produce the same result ("Done") whether I put the

System.out.println("Done") 

in the finally clause or not.

Thanks in advance for the help.
- Rudy -

-------------------------------------------------------

try
{
System.out.println("Start program");
String[] temp = new String[1];
temp[0] = "Rudy";
System.out.println("temp[1]: " + temp[1]);
}
catch (Exception ex)
{
ex.printStackTrace();
}
 
System.out.println("Done");

[ March 29, 2007: Message edited by: Rudy Rusli ]

[Manhar Puri]

Rudy,

In the above case "Done" will not be printed if an exception occurs.

In case of finally no matter what happens in the try block the finally block of code is executed. You should put code like cleaning database connections in the finally block, since you always want to close the database connection no matter what!

Hope this helps.

-Manhar

[Joanne Neal]

Originally posted by Manhar Puri:

In the above case "Done" will not be printed if an exception occurs.

Yes it will. The stacktrace will be printed and then the code will carry on to print the final message.

Rudy
They only both do the same because you are catching the exception and then allowing the code to continue.
Compare

void printMethod() throws Exception
{
  try {
    System.out.println("Start program");
    String[] temp = new String[1];
    temp[0] = "Rudy";
    System.out.println("temp[1]: " + temp[1]);
  } finally {
    System.out.println("Done");
  }
}

and

void printMethod() throws Exception
{
  System.out.println("Start program");
  String[] temp = new String[1];
  temp[0] = "Rudy";
  System.out.println("temp[1]: " + temp[1]);
  System.out.println("Done");
}

[Paul Sturrock]

Originally posted by Manhar Puri:
Rudy,

In the above case "Done" will not be printed if an exception occurs.

Yes it will. However it wont be printed if an Error is raised between the try and the catch.

[marc weber]

Originally posted by Rudy Rusli:
I'm trying to understand the use of finally clause...

See the topic, What's finally for? from Thinking in Java.

[Smith Li]

Paul,

Could you please explain more what do you mean by error between the try and catch?
In my code, there is an error (ArrayIndexOutOfBoundException) between the try and catch.

>>>>
Yes it will. However it wont be printed if an Error is raised between the try and the catch.
>>>>

[Keith Lynn]

ArrayIndexOutOfBoundsException is not an Error.

I think Paul was talking about things like OutOfMemoryError or another subclass of Error.

[Rahul Shilpakar]

finally is used for releasing resources aquired by the threads so as there woldn't be any deadlock while fetching shared resource.

[Paul Sturrock]

Originally posted by Keith Lynn:
ArrayIndexOutOfBoundsException is not an Error.

I think Paul was talking about things like OutOfMemoryError or another subclass of Error.

Yes. Remember Errors are not Exceptions, but will have simmilar effects. Consider this:

public class Foo {
   public static void main(String [] args ) {
      try {
         throw new AssertionError("Something has gone wrong");  
      } catch (Exception e) {

      } finally {
          System.out.println("This will print");
      }
      System.out.println("But will this print?");
   }
}

[ April 02, 2007: Message edited by: Paul Sturrock ]