The tricky 'finally' statement

October 12, 2022

Here are four examples, where the finally statement is tricky. Generally speaking, one should avoid using the return statement and throwing an Exception in the finally block - these are just some illustrative examples.

Example 1

public static int a() {
        try {
            System.out.println("Print some message");
            return 1;
        } catch (Exception exception) {
            System.out.println("Print another message");
        } finally {
            return 2;
        }
    }

Example 2

public static int b() {
        try {
            return 1;
        } catch (Exception exception) {
            return 2;
        } finally {
            return 3;
        }
    }

Example 3

public static void c() throws Exception {
        try {
            return;
        } finally {
            throw new Exception("From finally!");
        }
    }

Example 4

public static void d() {
        try {
            return;
        } finally {
            System.out.println("From finally!");
        }
    }

---

Lastly, inside the main method, we can call the above methods:

public static void main(String[] args) {
        System.out.println(a());  // Print some message
                                  // 2

        System.out.println(b());  // 3

        // we need to handle the Exception first
        try {
            c();
        } catch (Exception exception) {
            System.out.println(exception.getMessage()); // From finally!
        }

        d();                      // From finally!
    }

But, why?

In the first example, the code under the try block is executed, and so should be the return statement therein. However, the finally overrides the return statement, therefore 2 is returned.

The same happens in the second example, where the finally block overrides the return statement in the try block, and in case an Exception is caught, the finally block overrides the return statement in the catch block too - ‘it is the last statement to be executed’.

Interestingly, in the third example, the finally block overrides the return statement in the try block, and throws an Exception instead. Therefore, the Exception is thrown, and the return statement is omitted.

Lastly, the finally block in the fourth example is even able to override the return statement in the try block, with a simple print statement, and a message is printed to the standard output. So, the return statement is omitted.

References

Oracle Java Documentation