Introduction

• Definition:
  • In Java, the finally block is a block of code that is always executed after the execution of a try block, regardless of whether an exception occurs or not.
  • Even if an exception is not caught by the catch block, the finally block will still execute.

• Use:
  • Release resources safely - Close files, database connections, or network streams to avoid resource leaks.
  • Perform cleanup tasks - Execute important tasks that must run, like resetting variables or clearing temporary data.
  • Maintain program reliability - Helps in writing robust and error-resistant programs.
  • Guarantee execution - Acts as a safety mechanism to make sure critical code is not skipped.

• Syntax:

  • try
    {
        // risky code that may throw exception
    } 
    catch (ExceptionClassType e)
    {
        // exception handling code
    } 
    finally
    {
        // cleanup code (always executes)
    }

• Example 1: Normal Execution

  • public class FinallyDemo1
    {
        public static void main(String[] args)
        {
            try
            {
                System.out.println("Inside try block");
                int data = 10 / 2; // no exception
                System.out.println("Result: " + data);
            } 
            catch (ArithmeticException e)
            {
                System.out.println("Exception caught: " + e);
            } 
            finally
            {
                System.out.println("Finally block always executes");
            }
    
            System.out.println("Rest of the code...");
        }
    }

    Output:

    Inside try block
    Result: 5
    Finally block always executes
    Rest of the code...

• Example 2: Exception Occurs

  • public class FinallyDemo2
    {
        public static void main(String[] args)
        {
            try
            {
                System.out.println("Inside try block");
                int data = 10 / 0; // ArithmeticException
                System.out.println("Result: " + data);
            } 
            catch (ArithmeticException e)
            {
                System.out.println("Exception caught: " + e);
            } 
            finally
            {
                System.out.println("Finally block always executes");
            }
    
            System.out.println("Rest of the code...");
        }
    }

    Output:

    Inside try block
    Exception caught: java.lang.ArithmeticException: / by zero
    Finally block always executes
    Rest of the code...

Points to remember for finally block:

1. finally block executes whether exception occurs or not.
   • It executes even if we use return statement inside the try or catch block.

   • public class FinallyDemo3
     {
         public static void main(String[] args)
         {
             System.out.println(m1());
         }
     
         static String m1()
         {
             try
             {
                 System.out.println("Inside try");
                 return "Returning from try";
             } 
             catch (Exception e)
             {
                 return "Returning from catch";
             } 
             finally
             {
                 System.out.println("Finally block executed before return");
             }
         }
     }

     Output:

     Inside try
     Finally block executed before return
     Returning from try

2. The only cases where finally block may not execute
   • If the JVM exits using System.exit(0) before reaching finally.
   • If the program crashes due to a fatal error.