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Why is "else" rarely used after "if x then return"?

Asked 2010-07-16T04:06:12.083
70

This method:

boolean containsSmiley(String s) {
    if (s == null) {
        return false;
    }
    else {
        return s.contains(":)");
    }
}

can equivalently be written:

boolean containsSmiley(String s) {
    if (s == null) {
        return false;
    }

    return s.contains(":)");
}

In my experience, the second form is seen more often, especially in more complex methods (where there may be several such exit points), and the same is true for "throw" as well as "return". Yet the first form arguably makes the conditional structure of the code more explicit. Are there any reasons to prefer one over the other?

(Related: Should a function have only one return statement?)

java coding-style if-statement function-exit
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2 Answers

37

This is a pattern called Guard Clause. The idea is do all the checking upfront to reduce nested conditions to increase readability.

From the link:

double getPayAmount() {
    double result;
    if (_isDead) {
        result = deadAmount();
    } else {
        if (_isSeparated) {
            result = separatedAmount();
        } else {
            if (_isRetired) {
                result = retiredAmount();
            } else {
                result = normalPayAmount();
            }
        }
    }

    return result;
}

Using the Guard Clause, you'll get to see this result:

double getPayAmount() {
    if (_isDead) return deadAmount();
    if (_isSeparated) return separatedAmount();
    if (_isRetired) return retiredAmount();

    return normalPayAmount();
};
answered 2010-07-16T04:19:21.227
4

The else is redundant. Also some IDEs (Eclipse) and analysis tools (maybe FindBugs) may flag that as a warning or an error, so in that case programmers are likely to remove it.

answered 2010-07-16T04:15:32.980

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