Why Does Modifying a Variable in a Finally Block Not Affect the Returned Value?

Why Doesn't Modifying a Variable in a Finally Block Affect the Returned Value?

Java provides the try-finally statement, where code in the finally block is always executed, regardless of whether the try block completes normally or abruptly. However, this behavior can lead to unexpected results when a variable is modified in the finally block after a return statement is executed in the try block.

To illustrate this concept, consider the following Java class:

public class Test {

    private String s;

    public String foo() {
        try {
            s = "dev";
            return s;  // Return the value of s
        }
        finally {
            s = "override variable s";
            System.out.println("Entry in finally Block");
        }
    }

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

In this example, the foo method returns the string "dev" in the try block. However, the finally block modifies the s variable to "override variable s" and prints a message to indicate that it was executed.

Surprisingly, the output of this code is:

Entry in finally Block
dev

This result may seem counterintuitive because we would expect the value of s to be "override variable s" after the finally block is executed. However, this is not the case because:

• The return statement in the try block completes execution of the block and immediately returns the value of s at that point in time.
• Any changes made to the s variable in the finally block occur after the return statement has executed. Therefore, the returned value of s remains "dev" even though the finally block has modified it.

It's important to note that this behavior only applies to changes to the value of the s variable itself. If the s variable is a reference to a mutable object, changes to the contents of that object made in the finally block will be reflected in the returned value.

This detailed explanation clarifies why modifying a variable in a finally block does not change the return value of a method, even though the finally block is always executed.

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