How much ternary operator is allowed in Java

Introduction

This article is limited to Java.

The other day, I wrote the following article (I changed the title).

• Don't write the code if (isAdmin == true) in Java-Qiita

In this article, I've given the ternary operator as a good example:

String userType = isAdmin ? "Administrator" : "General";

However, there were quite a few reactions that the ternary operator was difficult to read. I intended to give it as a simple example, but I didn't explain it enough, so I will write a separate article.

My conclusion is that ** ternary operators can only be used for simple things **.

What is a ternary operator?

The ternary operator has the following form:

<Conditional expression> ? <Value when true> : <Value when false>

Before talking about which way to write, I will write an example of how much I feel "how much".

/*
 *White(Almost no problem)
 */
String userType = isAdmin ? "Administrator" : "General";

String userType = user.isAdmin() ? "Administrator" : "General";

UserType userType = user.isAdmin() ? UserType.ADMIN : UserType.NORMAL;

String userName = user.isAdmin() ? "Administrator" : user.getName();

/*
 *Gray close to white
 */
return user.getType() == UserType.GUEST ? "Guest user" : user.getName();

/*
 *Gray close to black
 */
String userName = user.getType() == UserType.GUEST ? "Guest user" : user.getName();

/*
 *black(out)
 */
String userName = user.getType() == UserType.GUEST ? "The guests" : user.getType() == UserType.ADMIN ? "Administrator" : user.getName() + "Mr.";

What is the standard

Return to the definition of the ternary operator.

<Conditional expression> ? <Value when true> : <Value when false>

In the previous example, what kind of pattern is good or bad can be classified as follows.

• White (almost no problem)
• Conditional expression
• boolean variable
• Method that returns boolean
• Value when true / false
• Constant * enum
• Simple calls such as getter
• Gray
• The conditional expression contains a comparison with == or ! =
• Black (out)
• Nested
• The value when true / false is other than a simple call

The reason why ternary operators are often disliked is that the cost of lexical analysis and grammatical analysis in the head is high, such as how much is a conditional expression and how much is a value when true. Also, the reason why comparisons with == and ! = Is not good is that they are mistaken for the substitution = and are confused for a moment.

Therefore, I try to avoid anything other than simple writing.

How to write

You could write something like this, but I don't like it because it's a negative solution.

String userName; //Initialization here is useless, so don't

if (user.getType() == UserType.GUEST) {
    userName = "The guests";
} else if (user.userType() == UserType.ADMIN) {
    userName = "Administrator";
} else {
    userName = user.getName() + "Mr.";
}

If you are yourself, create a method as follows. In this case, it can be implemented as a method of User class.

This time, I made an if statement to match the original conditional expression, but in the case of enum, I often use a switch statement.

private String getName(User user) {
    if (user.getType() = UserType.GUEST) {
        return "The guests";
    } else if (user.getType() == UserType.ADMIN) {
        return "Administrator";
    } else {
        return user.getName() + "Mr.";
    }
}

//Caller
String userName = getName(user);

in conclusion

There were more patterns that were harder to read than I expected. I think it's overkill to ban ternary operators, but I think it's okay to use only simple ones.