Swift中的类的继承,可以继承类的属性和方法,或是其他特性.子类也可以重写父类的方法或是属性.
class Vehicle { var currentSpeed = 0.0; var description:String{ return "traverling at \(currentSpeed) miles per hour" } func makeNoise(){ } }
/// 创建一个Vehicle 对象 let somevehicle = Vehicle() somevehicle.currentSpeed = 5; print("Vehicle:\(somevehicle.description)") // Vehicle:traverling at 5.0 miles per hour1.创建一个子类
/// 创建一个子类 继承于Vehicle class Bicycle: Vehicle { var hasBasket = false } let bicycle = Bicycle(); bicycle.hasBasket = true bicycle.currentSpeed = 15; print("Bicycle:\(bicycle.description)") // Bicycle:traverling at 15.0 miles per hour2.创建一个继承于Bicycle的子类
/// 创建一个子类 继承于Bicycle class Tandem: Bicycle { var currentNumberOfPassengers = 0 } let tandem = Tandem() tandem.hasBasket = true tandem.currentNumberOfPassengers = 2 tandem.currentSpeed = 22.0 print("Tandem: \(tandem.description)") // Tandem: traverling at 22.0 miles per hour3.重写 Overriding
3.1重写父类的方法
// 重写方法 class Train: Vehicle { override func makeNoise() { print("Choo Choo") } } let train = Train() train.makeNoise() // Choo Choo3.2 重写属性
// 重写属性 class SpeedLimitedCar: Vehicle { override var currentSpeed: Double { get { return super.currentSpeed } set { super.currentSpeed = min(newValue,40.0) } } } let limitedCar = SpeedLimitedCar() limitedCar.currentSpeed = 60.0 print("SpeedLimitedCar: \(limitedCar.description)") // SpeedLimitedCar: traverling at 40.0 miles per hour3.3重写属性监视器
class Car: Vehicle { var gear = 1 override var description: String { return super.description + " in gear \(gear)" } } let car = Car() car.currentSpeed = 25.0 car.gear = 3 print("Car: \(car.description)") // Car: traverling at 25.0 miles per hour in gear 3 // 重写属性监视器 class AutomaticCar: Car { override var currentSpeed: Double { didSet { gear = Int(currentSpeed / 10.0) + 1 } } } let automatic = AutomaticCar() automatic.currentSpeed = 35.0 print("AutomaticCar: \(automatic.description)") // AutomaticCar: traverling at 35.0 miles per hour in gear 44.防止重写
You can prevent a method,property,or subscript from being overridden by marking it asfinal. Do this by writing thefinal
modifier before the method,or subscript’s introducer keyword (such asfinal var
,final func
,monospace; word-wrap:break-word">final class func,andfinal subscript
).
Any attempt to override a final method,or subscript in a subclass is reported as a compile-time error. Methods,properties,or subscripts that you add to a class in an extension can also be marked as final within the extension’s deFinition.
You can mark an entire class as final by writing thefinal
modifier before theclass
keyword in its class deFinition (final class
). Any attempt to subclass a final class is reported as a compile-time error.
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