Common rationales

Abstract class require abstract method¶

Abstract modifier in a class is unnecessary if the class has no abstract methods.

abstract class Message {
    fun send() {
        // implementation
    }
}

Avoid primitive names¶

When declaring string and primitive variables, it is tempting to use simple names based on their type. In fact, they are usually recommendations given by the IDE. But these names are not descriptive and hard to understand what their purpose is.

val string = "Alice"

val int = 30

Concise brackets, parentheses and tags¶

Brackets and parentheses without content should be wrapped in a single line.

var emptyList = [
]
var emptyMap = [
  :
]

Hide utility class instance¶

To prevent instantiating a utility class, put a final modifier on the class and add a private constructor.

final class Strings {
    private Strings() {}

    static String capitalize(String str) {
        return str.substring(0, 1).toUpperCase() + str.substring(1);
    }
}

Move trailing elvis to the next line¶

In a multiline statement, the elvis operator should align with chained method calls instead of the same column.

val bananas =
    fruits
        .filter { it.type == BANANA }
        .takeUnless { it.isEmpty() } ?: return

No blank lines at initial, final and consecutive comments¶

Comment and block comment bodies should not have leading or trailing blank lines. No consecutive blank lines are allowed in the comment body.

/**
 *
 * The main function.
 *
 */
fun main() {
    // initialize the logger
    //
    //
    // and print the starting message
    val logger = Logger()
    logger.info("Starting the application")
}

Place built-in methods last¶

Built-in methods like toString, hashCode and equals are often placed at the end of the class. They are unrelated to the rest of the class and can be distracting when reading the source code.

class User(val firstName: String, val lastName: String) {
    var isAdmin: Boolean = false

    override fun toString(): String = "$lastName, $firstName"

    override fun hashCode(): Int = Objects.hash(firstName, lastName)

    override fun equals(other: Any?): Boolean {
        if (this === other) return true
        if (other !is Robot) return false
        return firstName == other.firstName && lastName == other.lastName
    }

    fun promote() {
        isAdmin = true
    }
}

Remove unused imports¶

Remove imports that are not used in the file.

import java.lang.String

val names = arrayListOf<String>()

Strip multiline brackets, parentheses and tags¶

Method declaration, calls and collection initializers should not start or end with a blank line.

def getColors(

    int red,
    int green,
    int blue
) {
    return [
        red,
        green,
        blue,

    ]
}