Superclass & Subclass
subclass子類別可以繼承Superclass父類別的方法與屬性。
若要生成兩個相似的物件，可以先寫Ａ類別（父類別）的程式碼生成一個物件，再寫Ｂ類別作為Ａ的子類別，Ｂ類別除了會繼承Ａ類別的方法與屬性，也能加入Ｂ類別自己特有的方法與屬性。

入虎穴

//Superclass
class Baby{
    var name:String
    var age:Int
    func sleep(){
        print("sleep")
    }
    func introduceSelf(){
        print("My name is \(name)")
    }
    init(){
        name = "Tom"
        age = 1
    }
    init(name:String){
        self.name = name
        self.age = 1
    }
    init(age:Int){
        self.age = age
        self.name = "Sophie"
    }
    init(name:String, age:Int){
        self.name = name
        self.age = age
    }
}

得虎子

//Subclass
class CuteBaby:Baby{
    //設置子類別自己的屬性及方法
    var nickname = "QQ"
    func danceAndSing(){
        print("dance and sing")
    }
}
let iAmSoQ:CuteBaby = CuteBaby()
iAmSoQ.name //Tom
iAmSoQ.sleep() //sleep
iAmSoQ.danceAndSing() //dance and sing
iAmSoQ.nickname //QQ

老子都不老子了
Override覆寫：子類別呼叫繼承的方法時，做出跟父類別不一樣的行為。

//Override
    override func sleep() {
        print("sleep with cute smile")
        super.sleep()
    override func introduceSelf() {
        print("My name is \(nickname)")
    }
}
iAmSoQ.sleep() 
//sleep with cute smile
//sleep
iAmSoQ.introduceSelf()
//My name is QQ

如何覆寫init方法？

1. 初始化子類別的屬性
2. super.init()
3. 設定服類別的屬性

override init(){
        nickname = "QQ"
        super.init()
        name = "Sunny"
    }