Why do we use finally blocks?

user_301459 0
Viewed 21614

As far as I can tell, both of the following code snippets will serve the same purpose. Why have finally blocks at all?

Code A:

try { /* Some code */ }
catch { /* Exception handling code */ }
finally { /* Cleanup code */ }

Code B:

try { /* Some code */ }
catch { /* Exception handling code */ }
// Cleanup code
finally java .net
11 Answers

Still scrolling down? Here you go!

This question gave me tough time back a while.

try
{
 int a=1;
 int b=0;
 int c=a/b;
}
catch(Exception ex)
{
 console.writeline(ex.Message);
}
finally
{
 console.writeline("Finally block");
}
console.writeline("After finally");

what would be printed in the above scenario? Yes guessed it right:

  • ex.Message--whatever it is (probably attempted division by zero)

  • Finally block

  • After finally

    try
{
    int a=1;
    int b=0;
    int c=a/b;
}
catch(Exception ex)
{
    throw(ex);
}
finally
{
    console.writeline("Finally block");
}
console.writeline("After finally");

What would this print? Nothing! It throws an error since the catch block raised an error.

In a good programming structure, your exceptions would be funneled, in the sense that this code will be handled from another layer. To stimulate such a case i'll nested try this code.

try
{    
 try
    {
     int a=1;
     int b=0;
     int c=a/b;
    }
    catch(Exception ex)
    {
     throw(ex);
    }
    finally
    {
     console.writeline("Finally block")
    }
    console.writeline("After finally");
}
catch(Exception ex)
{
 console.writeline(ex.Message);
}

In this case the output would be:

  • Finally block
  • ex.Message--whatever it is.

It is clear that when you catch an exception and throw it again into other layers(Funneling), the code after throw does not get executed. It acts similar to just how a return inside a function works.

You now know why not to close your resources on codes after the catch block.Place them in finally block.

user_114310680

finally block in java can be used to put "cleanup" code such as closing a file, closing connection etc.

The finally block will not be executed if program exits(either by calling System.exit() or by causing a fatal error that causes the process to abort).

user_113064340
Related