Break statements and flags #

A method with multiple boolean flags can be complex to read and/or debug, in particular when combined with break and/or continue statements.

This can usually be avoided:

using return statements (possibly with auxiliary functions), and/or
(in Java) using streams with anyMatch, allMatch or findFirst.

Example #

Exercise

Rewrite the following Java method:

without boolean flag and
without break statement.

/**
 * Returns true iff each of the input lists contains a number > 20
 */
boolean check(List<List<Integer>> lists) {

    boolean flag1 = true;
    boolean flag2 = false;

    for (List<Integer> list : lists) {
        for (int value : list) {
            if (value > 20) {
                flag2 = true;
                break;
            }
        }
        if (!flag2) {
            flag1 = false;
            break;
        }
    }
    return flag1;
}

Solution 1

With an auxiliary method:

boolean check(List<List<Integer>> lists) {

    for (List<Integer> list : lists) {
        if(!isValid(list)) {
            return false;
        }
    }
    return true;
}

private boolean isValid(List<Integer> values) {
    for (int value : values) {
        if(value > 20) {
            return true;
        }
    }
    return false;
}

Solution 2

boolean check(List<List<Integer>> lists) {
    return lists.stream()
        .allMatch(l -> l.stream().anyMatch(v -> v > 20));
}