class Planet { var name: String init(name: String) { self.name = name } convenience init() { self.init(name: "[No Planets]") } } let plName = Planet(name: "Mercury") print("行星的名字是: \(plName.name)") let noplName = Planet() print("没有这个名字的行星: \(noplName.name)") class planets: Planet { var count: Int init(name: String, count: Int) { self.count = count super.init(name: name) } override convenience init(name: String) { self.init(name: name, count: 1) } }