1.宣告Class

class A{
    var str = "Hello, Class"
    var number = 1

}
//建立類的例項
var a = A()
print(a.str)
//列印結果：Hello, Class

2.類與結構體不同，類沒有預設初始化方法。我們需要在類內部自己定義初始化方法傳參。

結構體可以直接寫為：

var a = A(str:"test",number:10)

但是用同樣方法寫類的時候是會報錯的，如果不自定義初始化方法，只能使用空初始化:

var a = A()

自定義初始化方法

class B{
    var str = "Hello, Class"
    var number = 1
    init(str: String,number: Int){
        self.str = str
        self.number = number
    }
    //無參初始化，委託初始化方法
//    convenience init(){
//        self.init(str: "Hello, Class",number: 1)
//    }
    //或者這樣定義也可以
    init() {
        str = "Declare as many initalisers as you want"
        number = 0
    }
}
var b = B(str: "Hello this is B", number: 2)
print("Default String is \(b.str) and Default number is \(b.number)")
//列印結果：Default String is Hello this is B and Default number is 2
 

如果自定義了初始化方法，此時申明空初始化會報錯；
提示：Missing arguments for parameters 'str', 'number' in call
此時，我們可以在類中宣告一個代理依託，宣告一個無參初始化。此時就不報錯了。

3.類繼承：類支援繼承，結構體不支援

子類繼承父類的特徵，然後可以對其進行優化，並新增新的特徵

class Animal{
    var isVeg : Bool
    var eats : String
    var numberOfLegs : Int
    init(isVeg: Bool, eats: String, numberOfLegs: Int) {
        self.isVeg = isVeg
        self.eats = eats
        self.numberOfLegs = numberOfLegs
    }
    func printProperties(){
        print("Is Veg? \(isVeg). Eats:\(eats). Number of legs:\(numberOfLegs)")
    }
}

var anim = Animal(isVeg: false, eats: "Can eat you", numberOfLegs: 4)
anim.printProperties()
//列印結果：Is Veg? false. Eats:Can eat you. Number of legs:4
 

建立子類

class Tiger : Animal{
    //Add class specific implementaion
}
var tiger = Tiger(isVeg: false, eats: "Can eat you", numberOfLegs: 4)
tiger.printProperties()
//列印結果：Is Veg? false. Eats:Can eat you. Number of legs:4

需要重寫父類中的函式時，需要用override修飾函式名

class Tiger : Animal{
    override func printProperties() {
        super.printProperties()
        print("This is Subclass Tiger")
		}
}
var tiger = Tiger(isVeg: false, eats: "Can eat you", numberOfLegs: 4)
tiger.printProperties()
//列印結果：
//Is Veg? false. Eats:Can eat you. Number of legs:4
//This is Subclass Tiger
 

下面例子是在子類中新增新屬性

class Tiger : Animal{
    var color : String
    override func printProperties() {
        //呼叫父類這個方法，會多列印一個結果，所以在重寫父類方法時，也可以不加這個
//        super.printProperties()
        print("This is tiger Is Veg \(isVeg). Eats:\(eats). Number of legs:\(numberOfLegs).color \(color)")
    }
    init(isVeg: Bool, eats: String, numberOfLegs: Int,color:String) {
        self.color = color
        //如果想要在子類中引用父類的屬性或函式，使用super.呼叫
        super.init(isVeg: isVeg, eats: eats, numberOfLegs: numberOfLegs)
    }
}
var tiger = Tiger(isVeg: false, eats: "Can eat you", numberOfLegs: 4,color: "yellow")
tiger.printProperties()
//列印結果：This is tiger Is Veg false. Eats:Can eat you. Number of legs:4.color yellow

類與結構體的另一個區別就是：類是引用型別的，結構體是值型別

var tiger = Tiger(isVeg: false, eats: "Can eat you", numberOfLegs: 4, color: "White")
tiger.printProperties()
//列印結果：This is tiger Is Veg false. Eats:Can eat you. Number of legs:4.color White
/ar tiger1 = tiger
tiger1.color = "Yellow"
tiger1.printProperties()//列印結果：This is tiger Is Veg false. Eats:Can eat you. Number of legs:4.color Yellow
tiger.printProperties()//列印結果：This is tiger Is Veg false. Eats:Can eat you. Number of legs:4.color Yellow

tiger.eats = "they can eat everything"
tiger1.printProperties()
tiger.printProperties()
//列印結果：This is tiger Is Veg false. Eats:they can eat everything. Number of legs:4.color Yellow
//列印結果：This is tiger Is Veg false. Eats:they can eat everything. Number of legs:4.color Yellow

4.便利初始化：設定屬性值的初始值

class A {
    var eyes: Int
    var legs: Int
    init(eyes: Int, legs: Int) {
        self.eyes = eyes
        self.legs = legs
    }
    
    
    convenience init() {
        self.init(eyes: 2, legs: 4)
    }

}

var a = A()
print(a.eyes) //prints 2
print(a.legs) //prints 4

便利初始化，只有當類中已經聲明瞭init()時，才可以定義