重寫實例方法
在子類中,你可以重寫繼承來的實例方法或類方法,提供一個定製或替代的方法實現。
class Person{
var name:String
var age:Int
func description() -> String{ //定義實例方法description
return "\(name) 年齡是: \(age)"
}
class func printClass() -> (){
print("Person 打印...") //靜態方法不能訪問實例屬性
}
init(name:String, age:Int){
self.name = name
self.age = age
}
}
class Student:Person{
var school:String
convenience init(){
self.init(name:"Tony", age:18, school:"四川師範大學")
}
init(name:String, age:Int, school:String){
self.school = school
super.init(name:name, age:age)
}
override func description() -> String { //在子類中重寫方法
print("父類打印 \(super.description())") //調用父類方法,super代指父類
return "\(name) 年齡是: \(age), 所在學校: \(school)。"
}
override class func printClass() ->(){ //重寫靜態方法
print("Student 打印...")
}
}
let student1 = Student()
print("學生1: \(student1.description())")
Person.printClass()
Student.printClass()
//輸出結果:
//父類打印 Tony 年齡是:18
//學生1:Tony 年齡是:18,所在學校:清華大學。
//Person 打印...
//Student 打印...
重寫靜態方法
靜態方法使用class或static關鍵字,但是使用哪一個要看子類中是否重寫該方法。class修飾的靜態方法可以被重寫,static關鍵字的就不能。
class Account{
var owner:String = "Tony" //賬戶名
//class不能換成static
class func interestBy(amount:Double) -> Double{ //定義靜態方法
return 0.08886 * amount
}
}
class TermAccount:Account{ //定期賬戶
//class可以換成static
override class func interestBy(amount:Double) -> Double{ //重寫靜態方法 這裏的class可以換成static 除非在TermAccount的子類重寫interestBy
return 0.09 * amount
}
}
//調用靜態方法
print(Account.interestBy(10_000.00))
print(TermAccount.interestBy(10_000.00))
下標重寫
對下標的重寫同子類屬性重寫一樣也是重寫下標的getter和setter訪問器
class DoubleDimensionalArray{
let rows:Int, columns:Int
var grid:[Int]
init(rows:Int, columns:Int){
self.rows = rows
self.columns = columns
grid = Array(repeating:0, count:rows * columns)
}
subscript(row:Int , col:Int)->Int{ //定義下標
get{
return grid[(row * columns) + col]
}
set{
grid[(row * columns) + col] = newValue
}
}
}
class SquareMatrix:DoubleDimensionalArray{ //類的繼承
override subscript(row:Int, col:Int)->Int{ //重寫父類下標
get{
return super.grid[(row * columns) + col]
}
set{
super.grid[(row * columns) + col] = newValue * newValue//給父類grid屬性附值
}
}
}
var ary2 = SquareMatrix(rows: 5, columns: 5)
for var i in 0..<5{
for var j in 0..<5{
ary2[i, j] = i + j
}
}
for var i in 0..<5{
for var j in 0..<5{
print("\t \(ary2[i, j])", terminator:" ")
}
print("\n")
}
使用final關鍵字
我們可以在類的定義中使用final關鍵字聲明類、屬性、方法和下標。final聲明的類不能被繼承,final聲明的屬性、方法、和下標不能被重寫。
final class Person{ //聲明final ,說明Person類不能被繼承
var name:String
final var age:Int
final func description() -> String{
return "\(name) 年齡是: \(age)"
}
final class func printClass() -> (){
print("Person 打印...")
}
init(name:String, age:Int){
self.name = name
self.age = age
}
}
class Student:Person{ //報錯
var school:String
convenience init(){
self.init(name: "Tony", age:18, school:"清華大學")
}
init(name:String, age:Int, school:String){
self.school = school
super.init(name:name, age:age)
}
override func description() -> String { //報錯
print("父類打印 \(super.description())")
return "\(name) 年齡是: \(age), 所在學校: \(school)。"
}
override class func printClass() -> (){ //報錯
print("Student 打印...")
}
override var age:Int{ //報錯
get{
return super.age
}
set{
super.age = newValue < 8 ? 8: newValue
}
}
}
類型檢查與轉換
定義一個類的繼承
class Person{
var name:String
var age:Int
func description() -> String{
return "\(name) 年齡是: \(age)"
}
convenience init(){//便利構造函數
self.init(name: "Tony")//調用本類的第二個(其他)便利構造函數
self.age = 19
}
convenience init(name:String){//便利構造函數
self.init(name: name, age:8)//調用同一類(下面)的指定構造函數
}
init(name:String, age:Int){//指定構造函數
self.name = name
self.age = age
}
}
class Student:Person{
var school:String
init (name:String, age:Int, school:String){//指定構造函數
self.school = school
super.init(name:name, age:age)//調用Person中的指定構造函數
}
}
class Worker:Person{
var factory:String
init(name:String, age:Int, factory:String){
self.factory = factory
super.init(name:name, age:age)
}
}
使用is進行類型檢查,它可以判斷一個實例是否是某個類的類型。如果實例是目標類型,結果返回true,否則返回false
let student1 = Student(name:"Tom", age:18, school:"清華大學")
let student2 = Student(name: "Ben", age: 28, school: "北京大學")
let student3 = Student(name: "Tony", age: 38, school: "香港大學")
let worker1 = Worker(name: "Tom", age: 18, factory: "鋼廠")
let worker2 = Worker(name: "Ben", age: 20, factory: "電廠")
let people = [student1, student2, student3, worker1, worker2]//把實例放進數組集合中
var studentCount = 0
var workerCount = 0
for item in people{ //用循環判斷其屬於哪個子類
if item is Worker{
workerCount = workerCount + 1
}else if item is Student{
studentCount = studentCount + 1
}
}
print("工人人數: \(workerCount), 學生人數: \(studentCount)。")
使用as、as!和as?進行類型轉換
某類型的一個常量或變量可能在幕後實際上屬於一個子類。當確定是這種情況時,你可以嘗試向下轉到它的子類型,用類型轉換操作符(as? 或 as!)。
因爲向下轉型可能會失敗,類型轉型操作符帶有兩種不同形式。條件形式(conditional form)as? 返回一個你試圖向下轉成的類型的可選值(optional value)。強制形式 as! 把試圖向下轉型和強制解包(force-unwraps)轉換結果結合爲一個操作。
//當你不確定向下轉型可以成功時,用類型轉換的條件形式(as?)。條件形式的類型轉換總是返回一個可選值(optional value),並且若下轉是不可能的,可選值將是 nil。這使你能夠檢查向下轉型是否成功。只有你可以確定向下轉型一定會成功時,才使用強制形式(as!)。當你試圖向下轉型爲一個不正確的類型時,強制形式的類型轉換會觸發一個運行時錯誤。
let p1:Person = Student(name: "Tom", age: 20, school: "清華大學")
let p2:Person = Worker(name: "Tom", age: 18, factory: "鋼廠")
let p3:Person = Person(name: "Tom", age: 28)
let p4:Student = Student(name: "Ben", age: 40, school: "北京大學")
let p5:Worker = Worker(name: "Tony", age: 28, factory: "電廠")
創建了實例,p1、p4是Student實例,p2、p5是Work實例,p3是Person實例
類型轉換有兩個方向:向下轉型——將父類類型轉換爲子類類型,向上轉型——將子類類型轉換爲父類類型。通常情況下的類型轉換都是向下轉型
as操作符在類中僅僅只用於向上轉型,很少用.還可以進行模式匹配
let p41:Person = p4 as Person//向上轉型
let p41:Person = p4
將Student類型的p4轉化爲Person類型是向上轉型,向上轉型通常可以省略as Person部分。
as!操作符可以應用於三種情況:將非可選類型爲非可選類型/將可選類型爲非可選類型/將可選類型爲可選類型
//1.將非可選類型爲非可選類型
let p11 = p1 as! Student
//let p111 = p2 as! Student //報錯 在轉換過程中不能轉換爲目標類型
//2.將可選類型爲非可選類型
let p6 :Person? = Student(name: "Tom", age: 20, school: "清華大學")
let p12 = p6 as! Student//報錯 p6爲nil as!在轉換過程對可選址進行拆包
//3.將可選類型爲可選類型
let p13 = p6 as! Student?//可選類型轉換爲可選類型
as?操作符可以應用於兩種情況:將非可選類型爲可選類型, 將可選爲可選
//向上轉型,使用as?
//將非可選類型爲可選類型
let p21 = p1 as? Student
let p211 = p2 as? Student
print(p21)
print(p211)
//將可選爲可選
let p7 :Person? = Student(name: "Tom", age: 20, school: "清華大學")
let p22 = p7 as? Student?
print(p7)
print(p22)
var arr = [p1, p2, p3, p4, p5]
var i:Int = 1
for item in arr{
if let m = item as? Worker{
print("Worker factory: \(m.factory)")
}else if let n = item as? Student{
print("Student school: \(n.school)")
}
i += 1
}
let stud1 = arr[0] as? Student //它是Student可選類型,具體使用時往往還需要拆包
print(stud1)
print(stud1!.school)
let woker1 = arr[1] as! Worker
print(woker1)
print(woker1.name)
所以我們在使用as?操作符進行類型轉換時你最好採用可選綁定方式,也就是將轉換語句放到if或while語句中
兩種不確定的類型:Any類型和AnyObject類型
AnyObject:任何類的類型, Any:任何類型
let people1:[Person] = [student1, student2, student3, worker1, worker2]
let people2:[AnyObject] = [student1, student2, student3, worker1, worker2]
let people3:[Any] = [student1,student2,student3, worker1, worker2]
for item in people2{
if let Student = item as? Student{
print("Student school: \(Student.school)")
}else if let Worker = item as? Worker{
print("Worker factory: \(Worker.factory)")
}
}
let w1:AnyObject = arr[1] as! Worker
使用Any類型來和混合的不同類型一起工作,包括函數類型和非類類型
var things = [Any]()//創建了一個可以存儲Any類型的數組
things.append(0)
things.append(0.0)
things.append(42)
things.append(3.14159)
things.append("hello")
things.append((3.0, 5.0))
things.append(Student(name: "Tina", age: 10, school: "四川師範大學"))
things.append({ (name: String) -> String in "Hello, \(name)" })
print("\n")
for thing in things {
switch thing {
case 0 as Int:
print("zero as an Int")
case 0 as Double:
print("zero as a Double")
case let someInt as Int:
print("an integer value of \(someInt)")
case let someDouble as Double where someDouble > 0:
print("a positive double value of \(someDouble)")
case is Double:
print("some other double value that I don't want to print")
case let someString as String:
print("a string value of \"\(someString)\"")
case let (x, y) as (Double, Double):
print("an (x, y) point at \(x), \(y)")
case let stu as Student:
print("a student name: '\(stu.name)', age: \(stu.age), school: \(stu.school)")
case let stringConverter as (String) -> String:
print(stringConverter("Michael"))
default:
print("something else")
}
}
原則上若能夠使用具體的數據類型,則儘量不要使用AnyObject類型,更要少考慮使用Any類型。從集合取出這些實例時,請儘可能地將AnyObject或Any類型轉換爲特定類型,然後在進行接下來的操作