一个类可以继承(inherit)另一个类的方法(methods)，属性(properties)和其它特性
类可以调用和访问超类的方法，属性和下标(subscripts)，并且可以重写(override)这些方法，属性和下标来优化或修改它们的行为。
可以为类中继承来的属性添加属性观察器(property observers)
1 基类(base class)
class Vehicle {
var currentSpeed = 0.0
var description: String {
return "traveling at \(currentSpeed) miles per hour"
}
func makeNoise() {
// 什么也不做-因为车辆不一定会有噪音
}
}
let someVehicle = Vehicle()
2 子类生成(Subclassing)
class Bicycle: Vehicle {
var hasBasket = false
}
let bicycle = Bicycle()
bicycle.hasBasket = true
bicycle.currentSpeed = 15.0
print("Bicycle: \(bicycle.description)")
class Tandem: Bicycle {
var currentNumberOfPassengers = 0
}
3 重写(Overriding)
任何缺少override关键字的重写都会在编译时被诊断为错误。
访问超类的方法，属性及下标。 super
class Train: Vehicle {
override func makeNoise() {
print("Choo Choo")
}
}
let train = Train()
train.makeNoise()
class Car: Vehicle {
var gear = 1
override var description: String {
return super.description + " in gear \(gear)"
}
}
class AutomaticCar: Car {
override var currentSpeed: Double {
didSet {
gear = Int(currentSpeed / 10.0) + 1
}
}
}
4 防止重写 (final var, final func, final class func, final subscript)
playground文件在andyRon/LearnSwift
