Try , finally execution flow when return is in try

Question

When try , finally combination is used, in try if there is a return statement.Why is finally block executed first?

---

class Palindrome
{
    public static void main(String args[]) 
    { 
        System.out.println(Palindrome.test()); 
    }

    public static int test()
    {
        try {  
                //return 0;  
                return 100;
        }  
        finally {  
            System.out.println("finally trumps return.");
        }
    }
}

In the above code please tell me the flow of execution. I know that finally will be executed mandatorily after the try block.But in try block, return staatement will take the control to main class. In that case how will the control come to finally block?

Answer 1

Because that's the definition of a finally block. It always happens, regardless of how the block is exited. Finally blocks exist for operations that SHOULD always be performed, like closing open streams and cleaning up socket connections. No matter how the block is exited, the code within the finally block should always be performed. If you want to skip code if the try block is exited successfully, then it belongs in a catch() block with an appropriate exception type.

Answer 2

What do you mean by "first"?

The finally runs before execution leaves the method. When else should it run? It is, after all, part of the method.

But if you have

int x = 1;
try{
   return x;
} finally {
   x = x + 1;
}

then the method will still return 1. So the return statement does get executed before the finally block in a way (to determine the return value).

If the question is why the finally block is executed at all, well, that's what they are for: To "finally" run after the "try" block is done, no matter what.

But in try block, return statement will take the control to main class. In that case how will the control come to finally block?

How? Well, that's just how the language (and runtime) work.

Before control flow is returned to the calling method, the finally block is executed.

It technically even has the option to change the return value (by having its own return statement), but that is highly discouraged.

Answer 3

From https://docs.oracle.com/javase/tutorial/essential/exceptions/finally.html

Finally block is to design to always execute:

The finally block always executes when the try block exits. This ensures that the finally block is executed even if an unexpected exception occurs. But finally is useful for more than just exception handling — it allows the programmer to avoid having cleanup code accidentally bypassed by a return, continue, or break. Putting cleanup code in a finally block is always a good practice, even when no exceptions are anticipated.

If you return in try block and code in finally block is not executed, this is not "always executes".

This makes code more readable if we do something necessary in finally block like unlock lock ,cleanup resources,which prevent some other new programmer(or yourself) add some code that returns or introduces exceptions in try block but without cleaning up the resources.

public static void main(String[] args) throws IOException {
    InputStream is;
    try {
        is = getInpustStreamFromNetwork();
        int i = 1 / 0;// 1. Intruduces exceptions
        return;// 2. returns before clean up resources
    } finally {
        is.close();// clean up resources is important, so it is a good practice to put it into finally block even though there is no exceptions to catch.
        System.out.println("no matter #1 or #2 ,this will be executed\n,");
    }
}

Answer 4

From https://docs.oracle.com/javase/tutorial/essential/exceptions/finally.html

The finally block always executes when the try block exits. This ensures that the finally block is executed even if an unexpected exception occurs. But finally is useful for more than just exception handling — it allows the programmer to avoid having cleanup code accidentally bypassed by a return, continue, or break. Putting cleanup code in a finally block is always a good practice, even when no exceptions are anticipated

There are some cases were the finally block may not execute. Follow the link to see what those are.

Thus the answer to your question is by design. Java is designed to work that way.