Class 상속

open class Base{

  init{

  Log.i(“KMJ”, “this is Base Class”);

  }

  constructor(b1:String,b2:String){

  Log.i(“KMJ”, “this is Base Class Constructor with 2param $b1/$b2”);

  }

  constructor(b1:String,b2:String,b3:String){

  Log.i(“KMJ”, “this is Base Class Constructor with 3param $b1/$b2/$b3”);

  }

}

class Topping:Base{

  init{

  Log.i(“KMJ”, “this is Topping Class”);

  }

  constructor(b1:String,b2:String):super(b1,b2){

  Log.i(“KMJ”, “this is Topping Class Constructor with 2param $b1/$b2”);

  }

  constructor(b1:String,b2:String,b3:String):super(b1,b2,b3){

  Log.i(“KMJ”, “this is Topping Class Constructor with 3param $b1/$b2/$b3”);

  }

}


val topping2=Topping(“topping1”, “topping2”);

val topping3=Topping(“topping1”, “topping2”, “topping3”);

 

 

 

• 초기화 순서 : Base Class(primary constructor(property, init) → sub constructor) → Topping Class(primary constructor(property, init) → sub constructor)

2020-10-29 15:38:43.101 13520-13520/com.example.kotlinstudy I/KMJ: this is Base Class
2020-10-29 15:38:43.101 13520-13520/com.example.kotlinstudy I/KMJ: this is Base Class Constructor with 2 param topping1 / topping2
2020-10-29 15:38:43.101 13520-13520/com.example.kotlinstudy I/KMJ: this is Topping Class
2020-10-29 15:38:43.101 13520-13520/com.example.kotlinstudy I/KMJ: this is Topping Class Constructor with 2 param topping1 / topping2
2020-10-29 15:38:43.101 13520-13520/com.example.kotlinstudy I/KMJ: this is Base Class
2020-10-29 15:38:43.101 13520-13520/com.example.kotlinstudy I/KMJ: this is Base Class Constructor with 3 param topping1 / topping2 / topping3
2020-10-29 15:38:43.101 13520-13520/com.example.kotlinstudy I/KMJ: this is Topping Class
2020-10-29 15:38:43.101 13520-13520/com.example.kotlinstudy I/KMJ: this is Topping Class Constructor with 3 param topping1 / topping2 / topping3

 

• primary constructor : Topping Class에 primary constructor가 있는 경우 Base Class도 primary constructor를 명시해주어야 함

open class Base(p: Int)

class Derived(p: Int) : Base(p)

 

• 기본 생성자 : sub constructor 생성 시 자동 생성되지 않으므로 선언 필요(Base Class가 sub constructor을 가지고 있는 경우에는 Topping Class의 sub constructor에서 명시적 위임을 해줘야 함)

 

1. 기본 생성자만 있는 경우, Base Class에 ()를 선언하든 안하든 상관없음(but empty primary constructor not recommended)

open class Base{ // Base()도 상관없음

…

}

class Topping : Base(){

…

}

val topping = Topping();

 

2. 암시적인 기본 생성자 위임(Base Class에 sub constructor 있는 경우 에러)

open class Base{

    init{

    Log.i(“KMJ”, “this is Base Class”);

    }

}



class Topping : Base{

    init{

    Log.i(“KMJ”, “this is Topping Class”);

    }

    constructor(b1 : String, b2 : String){ // Topping의 기본 생성자 위임이 생략됨(this())

    Log.i(“KMJ”, “this is Topping Class Constructor with 2 param $b1 / $b2”);

    }

    constructor(b1 : String, b2 : String, b3 : String){ // Topping의 기본 생성자 위임이 생략됨(this())

    Log.i(“KMJ”, “this is Topping Class Constructor with 3 param $b1 / $b2 / $b3”);

    }

}

val topping = Topping(); // 에러

val topping1 = Topping(“topping1”, “topping2”);

val topping2 = Topping(“topping1”, “topping2”, “topping3”);

 

2020-10-29 17:48:42.567 16403-16403/com.example.kotlinstudy I/KMJ: this is Base Class
2020-10-29 17:48:42.567 16403-16403/com.example.kotlinstudy I/KMJ: this is Topping Class
2020-10-29 17:48:42.567 16403-16403/com.example.kotlinstudy I/KMJ: this is Topping Class Constructor with 2 param topping1 / topping2
2020-10-29 17:48:42.567 16403-16403/com.example.kotlinstudy I/KMJ: this is Base Class
2020-10-29 17:48:42.567 16403-16403/com.example.kotlinstudy I/KMJ: this is Topping Class
2020-10-29 17:48:42.567 16403-16403/com.example.kotlinstudy I/KMJ: this is Topping Class Constructor with 3 param topping1 / topping2 / topping3