Swift 2 学习笔记 14.继承和构造函数

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继承和构造函数

• 继承基础

class Role {
    var name: String
    var life = 100 {
        didSet{
            if life < 0 {
                self.isAlive = false
            }
            self.isAlive = true
        }
    }
    var isAlive: Bool = true
    
    init(name: String) {
        self.name = name
    }
    
    func beAttacked(attack: Int) {
        life -= attack
    }
}

class User: Role {
    var score = 0
    
    func getScore(score: Int) {
        self.score += score
    }
}

// final 不允许再继承
final class Warrior: User {
    var weapon: String?
}

class Monster: Role {
    func  attack(user: User, amount: Int) {
        user.beAttacked(attack: amount)
    }
}

let player = Warrior(name: "bobo")
player.name  // "bobo"
player.life  // 100
player.isAlive  // true

player.beAttacked(attack: 110)
player.life  // -10
player.isAlive  // false

• 多态性

let player1 = Warrior(name: "bobo")
let monster1 = Monster(name: "monster1")

// 可以将不同的类统一进行操作
func printRoleName (role: Role) {
    print(role.name)
}

printRoleName(player1)  // "bobo"
printRoleName(monster1)  // "monster"

• 重载

final class Warrior: User {
    var weapon: String?
    // 重载
    override func beAttacked(attack: Int) {
        life -= attack/2
    }
}

class User: Role {
    var score = 0
    
    // 不允许被重载
    final func getScore(score: Int) {
        self.score += score
    }
}

• 两段式构造

class Role {
    var name: String
    var life = 100 {
        didSet{
            if life < 0 {
                self.isAlive = false
            }
            self.isAlive = true
        }
    }
    var isAlive: Bool = true
    
    init(name: String) {
        self.name = name
    }
}

class User: Role {
    var score = 0
    var group: String
    
    init(name:String, group: String) {
        // 构造初值
        self.group = group
        super.init(name: name)
        
        // 进一步完善
        if group == "" {
            self.getScore(score: -10)
        }
    }
    
    final func getScore(score: Int) {
        self.score += score
    }
}

• 便利构造函数和指定构造函数

class Role {
    var name: String
    var group: String
    
    init(name: String, group: String) {
        self.name = name
        self.group = group
    }
    
}

class User: Role {
    override init(name: String, group: String) {
        if group == "" {
            let defaultGroup = "default"
            super.init(name: name, group: defaultGroup)
            return
        }
        super.init(name: name, group: group)
    }
    
    convenience init(name: String = "visitor"){
        self.init(name: name, group: "")
    }
}

let visitor1 = User()
visitor1.name  // "visitor"
visitor1.group  // "default"

• 构造函数的继承

class Role {
    var name: String
    var group: String
    
    init(name: String, group: String) {
        self.name = name
        self.group = group
    }
    
    convenience init(firstName: String, lastName: String, group: String){
        let name  = firstName + " " + lastName
        self.init(name: name, group: group)
    }
    
}

class User: Role {
    override init(name: String, group: String) {
        if group == "" {
            let defaultGroup = "default"
            super.init(name: name, group: defaultGroup)
            return
        }
        super.init(name: name, group: group)
    }
    
    convenience init(name: String = "visitor"){
        self.init(name: name, group: "")
    }
}

class Monster: Role {
    convenience init(type: String) {
        // 自己的指定构造函数是由父类继承而来
        self.init(name: type, group: type)
    }
}

// 如果子类实现了父类所有的指定构造函数，则自动继承父类的的所有便利构造函数
let visitor1 = User(firstName: "John", lastName: "Snow", group: "Ice and Fire")

// 如果子类没有实现任何父类的指定构造函数，则自动继承父类的所有指定构造函数，并继承父类的便利构造函数
let monster1 = Monster(name: "monster", group: "monster")

• required构造函数

class Role {
    var name: String
    var group: String
    
    // 需要子类必须实现的构造函数
    required init(name: String, group: String) {
        self.name = name
        self.group = group
    }
}

class User: Role {
    // 子类重载父类指定的构造函数 override关键词更改为required
    required init(name: String, group: String) {
        if group == "" {
            let defaultGroup = "default"
            super.init(name: name, group: defaultGroup)
            return
        }
        super.init(name: name, group: group)
    }
}