Kotlin Documentation | Classes

Kotlin Documentation 시리즈에 대해

Category: Concepts - Classes and objects

문서 링크: https://kotlinlang.org/docs/classes.html

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Constructor

class Person constructor(firstName: String) { /*...*/ }

생성자에 어노테이션(e.g. class A @Inject constructor(…))이나 visibility modifiers가 없다면 constructor 키워드를 생략해도 된다:

class Person(firstName: String) { /*...*/ }

init

class InitOrderDemo(name: String) {
    val firstProperty = "First property: $name".also(::println)
    
    init {
        println("First initializer block that prints $name")
    }
    
    val secondProperty = "Second property: ${name.length}".also(::println)
    
    init {
        println("Second initializer block that prints ${name.length}")
    }
}

/*
First property: hello
First initializer block that prints hello
Second property: 5
Second initializer block that prints 5
*/

• Primary constructor
• constructor는 코드를 가질 수 없기 때문에 필요성이 대두되었다.

Trailing comma

class Person(
    val name: String,
    var age: Int, // trailing comma
) { /*...*/ }

With annotations or visibility modifiers

class Customer public @Inject constructor(name: String) { /*...*/ }

Secondary constructors

class Person(val name: String) {
    val children: MutableList<Person> = mutableListOf()
    constructor(name: String, parent: Person) : this(name) {
        parent.children.add(this)
    }
}