Swift 继承

基类

import UIKit

// 基类
class Vehicle {
    var currentSpeed = 0.0
    var description: String {
        return "traveling at \(currentSpeed) miles per hour"
    }
    
    func makeNoise() {
        
    }
}

let SomeVehicle = Vehicle()
print("Vehicle: \(SomeVehicle.description)")

console log 如下

定义基类.png

子类

// 子类
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
}

let tandem = Tandem()
tandem.hasBasket = true
tandem.currentNumberOfPassengers = 2
tandem.currentSpeed = 22.0
print("Tandem: \(tandem.description)")

console log 如下

定义子类.png

重写方法

// 重写方法
class Train: Vehicle {
    override func makeNoise() {
        print("Choo Choo")
    }
}

let train = Train()
train.makeNoise()

console log 如下

重写方法.png

重写计算属性

// 重写计算属性
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)")

console log 如下

重写计算属性.png

重写属性监听

// 重写属性监听
class AutomaticCar: Car {
    override var currentSpeed: Double {
        didSet {
            gear = Int(currentSpeed / 10.0) + 1
        }
    }
}

let automic = AutomaticCar()
automic.currentSpeed = 35.0
print("AutomaticCar: \(automic.description)")

console log 如下

重写属性监听.png

注意: 用final 关键字来阻止重写