# 코틀린OOP 실습 2주차

Exercise: Bank Account 

다음 속성(property)을 갖는 BankAccount 클래스를 만든다. 
• Account number (계좌마다 서로 다른 값) 
• Account holder name 
• Balance (계좌 잔액) 
BankAccount 클래스는 다음 메소드(method)를 갖는다. 
• Deposit (입금) 
• Withdraw (출금, 성공하면 true, 잔액이 모자라서 실패하면 false 리턴) 
• balance 속성 setter는 private으로 하여 외부에서 사용 금지 
아래 사용 예시의 코드가 동작하도록 한다. 

 

팁 
유일한 Account Number를 할당하기 위해, 새 BankAccount 객체가 생성될 때마다 값을 증가시키
는 카운트를 사용할 수 있다. 이 카운트는 companion object에 저장한다.

class BankAccount(val Name : String, var account : Double) {

    companion object {
        private var accountCount=10
    }
    val accountNumber:Int

    init{
        accountNumber=accountCount++
    }

    var balance:Double = account
    fun deposit(money : Double) {
        balance += money
    }
    fun withdraw(money : Double):String {
        if (balance>=money){
            balance-=money
            return "true"
        }
        else
            return "false"
    }
}


fun main() {
    val account = BankAccount("John Smith", 100.0)
    println(account.accountNumber) // Output: 10
    println(account.balance) // Output: 100.0
    println(BankAccount("James Baker", 10.0).accountNumber) // Output: 11
    // account.balance = 10
    // Compile Error (Cannot assign to 'balance': the setter is private in 'BankAccount')

    account.deposit(50.0)
    println(account.balance) // Output: 150.0

    val success = account.withdraw(75.0)
    println(success) // Output: true
    println(account.balance) // Output: 75.0

    val failure = account.withdraw(100.0)
    println(failure) // Output: false
    println(account.balance) // Output: 75.0
}

※ balance 값에 직접 접근할 때 컴파일 에러가 발생되는 부분을 추가 작성할 필요가 있음.

 

 

Exercise: Vehicle Inheritance 

여러 타입의 탈 것의 부모 클래스가 될 Vehicle 클래스를 만든다. Vehicle 클래스를 상속하여 Car, 
Motorcycle, Bicycle 등을 만들 수 있다. 
Vehicle 클래스는 다음 속성을 갖는다. 
• make (제조사) 
• model (모델명) 
• year (생산년도) 
Vehicle 클래스는 다음 메소드를 갖는다. 
• start (출발) 
• stop (정지) 
Car, Motorcyle, Bicycle 클래스를 Vehicle 클래스를 상속하여 만든다. 
Car 클래스는 다음의 추가 속성을 갖는다. 
• numDoors (차문의 수) 
Motorcycle 클래스는 다음의 추가 속성을 갖는다. 
• hasSidecar (사이드카를 갖는지 여부를 나타내는 Boolean) 
Bicycle 클래스는 다음의 추가 속성을 갖는다. 
• numGears (기어 수) 
각 서브클래스(Car, Motorcycle, Bicycle)는 자신의 start, stop 메소드를 갖는다. 예를 들어 Car의 
start는 키를 돌린다, Bicycle의 start는 페달을 밟는다와 같이 만든다. 실제로 이런 내용을 만들 수
는 없으니 println으로 해당 동작을 출력하도록 한다.

open class Vehicle(val make:String, val model:String, val year:Int){
    open fun start(){
        println("start")
    }
    open fun stop(){
        println("stop")
    }
}

class Car(make:String, model:String, year:Int, val numDoors:Int):Vehicle(make, model, year) {
    override fun start() {
        println("Turning key in ignition")
    }
    override fun stop() {
        println("Applying brakes and turning off engine")
    }
}

class Motorcycle(make:String, model:String, year:Int, val hasSidecar:Boolean):Vehicle(make, model, year) {
    override fun start() {
        println("Kicking starter")
    }
    override fun stop() {
        println("Applying brakes and turning off engine")
    }
}

class Bicycle(make:String, model:String, year:Int, val numGears:Int):Vehicle(make, model, year) {
    override fun start() {
        println("Pedaling")
    }
    override fun stop() {
        println("Applying brakes")
    }
}

fun list_name(vehicles: List<Vehicle>) {
    for (v in vehicles) {
        println("${v.make} ${v.model} ${v.year}")
    }
}
fun main() {
    val car = Car("Hyundai", "Casper", 2022, 4)
    val motorcycle = Motorcycle("Harley Davidson", "Fat Boy", 2022, true)
    val bicycle = Bicycle("Samchuly", "Lucia", 2022, 7)

    car.start()  // Output: Turning key in ignition...
    car.stop()
    // Output: Applying brakes and turning off engine...
    println(car.numDoors) // Output: 4

    motorcycle.start()  // Output: Kicking starter...
    motorcycle.stop()  // Output: Applying brakes and turning off engine...
    println(motorcycle.hasSidecar) // Output: true
    bicycle.start()  // Output: Pedaling...
    bicycle.stop()  // Output: Applying brakes...
    println(bicycle.numGears) // Output: 7

    list_name(listOf(car, motorcycle, bicycle))
    // Output:
    // Hyundai Casper 2022
    // Harley Davidson Fat Boy 2022
    // Samchuly Lucia 2022
}

 

 

 

Exercise: Vector Addition 

벡터 표현을 위한 Vector 클래스를 만들고 plus 연산자를 오버로딩한다. 
Vector 클래스는 다음 속성을 갖는다. 
• x (the x-coordinate of the vector) 
• y (the y-coordinate of the vector) 
Vector 클래스는 다음 메소드를 갖는다. 
• toString (벡터를 문자열로 변환, 예를 들어  (x, y) 와 같은 형태로 만든다.) 
• operator plus (두 벡터를 더한 결과를 리턴) 

data class Vector(val x:Int, val y:Int) {
    operator fun plus(other:Vector):Vector = Vector(x + other.x, y + other.y)
    override fun toString(): String = "($x, $y)"
}


fun main(){
    val v1 = Vector(1, 2)
    val v2 = Vector(3, 4)
    println(v1 + v2) // Output: (4, 6)
}