GotchaDifficulty: Intermediate1 min

finally and return: Why a finally Block Must Not Return

A method that returns 1 in its try block and hands its caller 2.

A finally block runs on every way out of a try, including a return: the return value is worked out, the finally runs, and only then does the method return. A return written inside the finally replaces that value, and discards any exception on its way out.

The ordinary case first, a try that returns and a finally that prints:

java

static int value() {
    try {
        return 1;
    } finally {
        System.out.println("finally ran");
    }
}

text

finally ran
1

A finally block runs on every way out of the try: falling off the end, returning, breaking, or throwing. The return on line 3 works out its value, then finally runs, then the method returns.

That much is useful and is what finally is for. The expensive version is a return inside the finally itself.

java

static int value() {
    try {
        return 1;
    } finally {
        return 2;
    }
}

Never return or throw from a finally block. Use it for cleanup and nothing else, and let whatever the try decided be what leaves the method.

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