Does the Finally Block Override a Returned Variable in Java?

Impact of Finally Block on Returned Variables: Understanding the Exception

In Java, the finally block ensures code execution regardless of try-catch block outcomes or abrupt terminations. However, it's crucial to understand how these blocks interact with returned variables.

Consider the following class:

public class Test {

    private String s;

    public String foo() {
        try {
            s = "dev";
            return s;
        }
        finally {
            s = "override variable s"; // This change doesn't affect the returned value
            System.out.println("Entry in finally Block");
        }
    }

    public static void main(String[] xyz) {
        Test obj = new Test();
        System.out.println(obj.foo()); // Prints "dev"
    }
}

Decoding the Unexpected Behavior

When the foo() method is invoked, the returned value is determined before the finally block executes. The try block completes with the return statement assigning "dev" to s, which becomes the returned value. The subsequent change to s within the finally block is not reflected in the returned value.

Understanding the Rules

According to the Java Language Specification, completing the try block with a return statement abruptly terminates it. The finally block runs after the abrupt termination, and if it completes normally, the try statement also abruptly terminates. Therefore, the return statement in the finally block overrides the return value determined within the try block.

Mutable Objects vs. Immutable Objects

Note that this behavior applies to the actual value of s, not the object it references. If s were a reference to a mutable object (such as an array or a custom class) and its contents were changed in the finally block, those changes would affect the returned value. However, String objects are immutable, so their values cannot be changed.

Conclusion

To summarize, the finally block cannot modify the returned variable in a try block. The value returned is determined before the finally block executes, and any subsequent changes to the variable's value within the finally block will not affect the returned result.

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