Exercise : "Boolean Zen"

This attempted solution to Self-Check 5.15 (isVowel) has several problems:

// Returns whether the given string represents a vowel:
// a, e, i, o, or u, case insensitively.
public static boolean isVowel(String s) {
    if (s == "a") {
        return true;
    } else if (s == "e") {
        return true;
    } else if (s == "i") {
        return true;
    } else if (s == "o") {
        return true;
    } else if (s == "u") {
        return true;
    } else {
        return false;
    }
}
  

Open Practice-It from the link above, copy/paste this code into it, then see the next slide.

Exercise - things to fix

Fix the following aspects of the code:

• It has a bug related to how strings are compared.
• It isn't case sensitive; it fails for uppercase vowels.
• It has too many unnecessary if/else statements.
• (advanced) It does not use "Boolean Zen" as described in textbook section 5.3.

Exercise - answer

public static boolean isVowel(String s) {
    s = s.toLowerCase();
    if (s.equals("a") || s.equals("e") || s.equals("i")
            || s.equals("o") || s.equals("u")) {
        return true;
    } else {
        return false;
    }
}
  

The above can be improved. "Boolean Zen" version:

public static boolean isVowel(String s) {
    s = s.toLowerCase();
    return s.equals("a") || s.equals("e") || s.equals("i")
           || s.equals("o") || s.equals("u");
}