finally block

The finally block always executes when the try block exits. This ensures that the finally block is executed even if an unexpected exception occurs. Finally block mainly used to perform clean up operation like closing file streams, flushing the data etc.,

A try block must associate with at least one catch or finally block.

Example

class ExceptionEx{
 public static void main(String args[]){
  try{
   System.out.println(10/0);
  }
  finally{
   System.out.println("I am finally block");
  }
  System.out.println("I am not going to executed");
 }
}

Output

I am finally block
Exception in thread "main" java.lang.ArithmeticException: / by zero
at ExceptionEx.main(ExceptionEx.java:5)

 

Observe the output, before throwing the exception, the code in the finally is executed. One more thing is above program doesn't handle the exception, so after executing the finally block, Java run time throws the exception and terminates the program.

finally always executes even the exception handled by the catch block.

Example

class ExceptionEx{
 public static void main(String args[]){
  try{
   System.out.println(10/0);
  }
  catch(Exception e){
   System.out.println(e);
  }
  finally{
   System.out.println("I am finally block");
  }
  System.out.println("I am done with execution");
 }
}

 

Output

java.lang.ArithmeticException: / by zero
I am finally block
I am done with execution

The runtime system always executes the statements within the finally block regardless of what happens within the try block.

class ExceptionEx{
 static int print(){
  try{
   return 10;
  }
  finally{
   System.out.println("I am finally block");
  }
 }

 public static void main(String args[]){
  int var = print();
  System.out.println("value of var is" + var);
 }
}

Output

I am finally block
value of var is10

  

Above program called the return statement, even then also finally executed.

Some Points To Remember

1. What is the Output of the below Program ?

class ExceptionEx{
 static int print(){
  try{
   return 10;
  }
  finally{
   return -1;
  }
 }

 public static void main(String args[]){
  int var = print();
  System.out.println("value of var is " + var);
 }
}

Output

value of var is -1

Since the finally block execute even prgram calls return from the try block. So the value returned by try block is 100 overridden by the value -1.

2. What is the output of the below Program ?

class ExceptionEx{
 static int print(){
  try{
   System.out.println(10/0);
  }
  catch(ArithmeticException e){
   System.out.println(e);
   return 100;
  }
  finally{
   return -1;
  }
 }

 public static void main(String args[]){
  int var = print();
  System.out.println("value of var is " + var);
 }
}

Output

java.lang.ArithmeticException: / by zero
value of var is -1

3. What are the situation that finally can't execute ?

a. If the JVM exits while the try or catch code is being executed, then the finally block may not execute

b. if the thread executing the try or catch code is interrupted or killed, the finally block may not execute.

4. What is the output of the below program ?

class ExceptionEx{
 static void print(){
  try{
   System.out.println("I am in try");
   System.exit(0);
  }
  finally{
   System.out.println("I am in finally");
  }
 }

 public static void main(String args[]){
  print();
 }
}

 

Output

I am in try

Calling system.exit() terminates the program, so finally can't execute.

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