How Does a Finally Block Affect the Return Value of a Method in Java?

Impact of Finally Block on Return Value

In Java, the behavior of a finally block on the return value of a method can be counterintuitive. Let's analyze a code snippet and delve into the underlying reasons for this phenomenon.

Consider the following code:

public class Test {

    private String s;

    public String foo() {
        try {
            s = "dev";
            return 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());
    }
}

When executed, the code prints "Entry in finally Block" but returns "dev." This is because the return value is determined by the execution of the return statement in the try block. The change made to 's' in the finally block occurs after the try block has completed and is therefore not reflected in the return value.

It's important to note that this applies to changes in the value of 's' itself, not to changes in the object 's' references. If 's' were a reference to a mutable object and its contents were changed in the finally block, those changes would be visible in the return value.

The Java Language Specification (JLS) outlines the detailed rules for this behavior in Section 14.20.2. In the case of a try-finally statement, if both the try block and the finally block have return statements, the return value of the finally block prevails. This is because the execution of a return statement is considered an abrupt termination of the block.

To summarize, the return value of a method is determined by the return statement within the try block. Changes made to the variable in a finally block, whether in value or through object modification, do not affect the return value unless the finally block also includes a return statement.

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