【Golang】快速複習指南QuickReview(七)——接口interface

在C#中,接口是實現多態的方式之一,但是接口更側重對象的能力,是一種規範。如果繼承了接口,就必須按照接口的要求去實現這個接口。接口與接口之間是可以有繼承,而且是多繼承。而golang中的接口,是一組方法的集合體,duck-type programming的一種體現。

如果有一種動物能夠想鴨子那樣行走,叫的也像鴨子,那麼我們認爲這就是鴨子。

1.C#的接口

前文提到,C#的接口側重於能力,好的接口功能(能力)單一,接口能繼承接口,類能繼承多個接口(多種能力),如果繼承了接口,就必須全部實現。

1.1 接口定義

接下來我們定義一個運動員IPlayer的接口:

public interface IPlayer
{
    //接口可以定義屬性
    string Name { get; set; }
    double Height { get; set; }
    int Age { get; set; }
    
    //運動
    void PlaySport();
}

1.2 接口繼承接口

再定義一個職業籃球運動員接口IBasketPlayer

  • 首先職業籃球運動員也是一個運動員,所以繼承運動員接口IPlayer
  • 其次,不管是哪個聯賽的職業運動員,除了有一些通用的技術能力,都會面臨轉會事件TransferEvent
public interface IBasketPlayer: IPlayer
{
        //臂展
        double Wingspan { get; }

        //垂直摸高
        double Verticalreach { get; }

        //垂直跳躍
        double Verticalleap { get; }

        //索引器  爲了演示,強行加一個索引器
        string this[string index]
        {
            get; set;
        }

        event EventHandler TransferEvent;


        //扣籃
        void Dunk();
        //傳球
        void Pass();
        void Dribble();
        //3分球
        void ThreePointShot();
        //中遠距離
        void TwoPointShot();
        //空接
        void AlleyOop();
        //籃板
        void Backboard();
}

1.3 實現接口

  • 定義一個NBA球員 NBAPlayer
public class NBAPlayer : IBasketPlayer
{
    //索引器
    public string this[string index] { get => throw new NotImplementedException(); set => throw new NotImplementedException(); }
    
    //臂展
    public double Wingspan => throw new NotImplementedException();
    
    //錘子摸高
    public double Verticalreach => throw new NotImplementedException();
    
    //垂直起跳
    public double Verticalleap => throw new NotImplementedException();
    
    //姓名
    public string Name { get => throw new NotImplementedException(); set => throw new NotImplementedException(); }
    
    //身高
    public double Height { get => throw new NotImplementedException(); set => throw new NotImplementedException(); }
    
    //年齡
    public int Age { get => throw new NotImplementedException(); set => throw new NotImplementedException(); }

    public event EventHandler TransferEvent;

    public void AlleyOop()
    {
        throw new NotImplementedException();
    }

    public void Backboard()
    {
        throw new NotImplementedException();
    }

    public void Dribble()
    {
        throw new NotImplementedException();
    }

    public void Dunk()
    {
        throw new NotImplementedException();
    }

    public void Pass()
    {
        throw new NotImplementedException();
    }

    public void PlaySport()
    {
        throw new NotImplementedException();
    }

    public void ThreePointShot()
    {
        throw new NotImplementedException();
    }

    public void TwoPointShot()
    {
        throw new NotImplementedException();
    }
}
  • 在定義一個CBA球員 實現接口CBAPlayer
public class CBAPlayer : IBasketPlayer
{
    //索引器
    public string this[string index] { get => throw new NotImplementedException(); set => throw new NotImplementedException(); }
    
    //臂展
    public double Wingspan => throw new NotImplementedException();
    
    //錘子摸高
    public double Verticalreach => throw new NotImplementedException();
    
    //垂直起跳
    public double Verticalleap => throw new NotImplementedException();
    
    //姓名
    public string Name { get => throw new NotImplementedException(); set => throw new NotImplementedException(); }
    
    //身高
    public double Height { get => throw new NotImplementedException(); set => throw new NotImplementedException(); }
    
    //年齡
    public int Age { get => throw new NotImplementedException(); set => throw new NotImplementedException(); }

    //轉會事件
    public event EventHandler TransferEvent;

    public void AlleyOop()
    {
        throw new NotImplementedException();
    }

    public void Backboard()
    {
        throw new NotImplementedException();
    }

    public void Dribbl()
    {
        throw new NotImplementedException();
    }

    public void Dunk()
    {
        throw new NotImplementedException();
    }

    public void Pass()
    {
        throw new NotImplementedException();
    }

    public void PlaySport()
    {
        throw new NotImplementedException();
    }

    public void ThreePointShot()
    {
        throw new NotImplementedException();
    }

    public void TwoPointShot()
    {
        throw new NotImplementedException();
    }
}

1.4 實現多個接口

NBA很多黑人球員,不但會打籃球,還會說唱,(黑人,人均會跳舞,會說唱,_),比較有名的有艾弗森,阿泰斯特,利拉德,尤其是艾弗森Allen Iverson,很多音樂平臺都能搜到,但是CBA球員就不一定會說唱,所以繼續定義一個說唱接口 IRapper

public interface IRapper
{
    void Rapper();
}
public class NBAPlayer : IBasketPlayer,IRapper
{
    //索引器
    public string this[string index] { get => throw new NotImplementedException(); set => throw new NotImplementedException(); }
    
    //臂展
    public double Wingspan => throw new NotImplementedException();
    
    //錘子摸高
    public double Verticalreach => throw new NotImplementedException();
    
    //垂直起跳
    public double Verticalleap => throw new NotImplementedException();
    
    //姓名
    public string Name { get => throw new NotImplementedException(); set => throw new NotImplementedException(); }
    
    //身高
    public double Height { get => throw new NotImplementedException(); set => throw new NotImplementedException(); }
    
    //年齡
    public int Age { get => throw new NotImplementedException(); set => throw new NotImplementedException(); }

    //轉會
    public event EventHandler TransferEvent;
    
    //會說唱
    public void Rapper()
    {
        throw new NotImplementedException();
    }
    

    public void AlleyOop()
    {
        throw new NotImplementedException();
    }

    public void Backboard()
    {
        throw new NotImplementedException();
    }

    public void Dribbl()
    {
        throw new NotImplementedException();
    }

    public void Dunk()
    {
        throw new NotImplementedException();
    }

    public void Pass()
    {
        throw new NotImplementedException();
    }

    public void PlaySport()
    {
        throw new NotImplementedException();
    }

    public void ThreePointShot()
    {
        throw new NotImplementedException();
    }

    public void TwoPointShot()
    {
        throw new NotImplementedException();
    }
}

2.Golang的接口

C#的接口可以說一種規範,它可以包含數據的規範,比如屬性,事件,索引器,也可以包含行爲(方法)的規範,但是Golang有所不同:Golang不關心數據,只關心行爲(方法)。

2.1 接口定義

接口是一種類型,抽象類型,就像定義struct一樣定義:

type Player interface {
	PlaySport()
}

2.2 實現接口

一個對象(能作爲方法的接收者)只要實現了接口中定義的方法,那麼就算實現了這個接口。

func main(){
    var player Player = &NBAPlayer{
        Name: "James",
    }

	player.PlaySport()
}
type Player interface {
	PlaySport()
}
type NBAPlayer struct {
	Name          string
	Height        float32
	Age           int8
	Wingspan      float32
	Verticalreach float32
	Verticalleap  float32
}
//指針接收者實現接口
func (p *NBAPlayer) PlaySport() {
	fmt.Println(p.Name, "從事的運動項目是打籃球")
}
James 從事的運動項目是打籃球

ps:如果是上面的代碼採用值接收者func (p NBAPlayer) PlaySport(),無論是結構體還是結構體指針都可以賦值給接口變量,因爲Go語言中有對指針類型變量求值的語法糖,結構體指針內部會自動求值*struct。如果是上面代碼那樣採用指針接收者,那麼接口變量就必須傳指針。這個問題如果不熟練,會在實際編碼中一次次被編譯器打臉。

2.3 實現多個接口

一個NBA球員既要實現Player接口,又要實現Rapper接口:

func main(){
    var player Player = &NBAPlayer{
        Name: "James",
    }
	var rapper Rapper = &NBAPlayer{
		Name: "James",
	}

	player.PlaySport()
	rapper.Rapper()
}
type Rapper interface {
	Rapper()
}
type Player interface {
	PlaySport()
}
type NBAPlayer struct {
	Name          string
	Height        float32
	Age           int8
	Wingspan      float32
	Verticalreach float32
	Verticalleap  float32
}
//指針接收者實現接口
func (p *NBAPlayer) PlaySport() {
	fmt.Println(p.Name, "從事的運動項目是打籃球")
}
func (p *NBAPlayer) Rapper() {
	fmt.Println(p.Name, "還會說唱")
}
James 從事的運動項目是打籃球
James 還會說唱

2.4 嵌套接口

接口BasketPlayer嵌套接口Player,Rapper,這個就類似於C#接口可以繼承接口。

func main(){
	var nbaplayer BasketPlayer = &NBAPlayer{
		Name: "Allen Iverson",
	}
	nbaer.PlaySport()
	nbaer.Rapper()
    nbaer.Dunk()
}
type BasketPlayer interface {
	Player
	Rapper
    Dunk()
}
func (p *NBAPlayer) PlaySport() {
	fmt.Println(p.Name, "從事的運動項目是打籃球")
}
func (p *NBAPlayer) Rapper() {
	fmt.Println(p.Name, "還會說唱")
}
func (p *NBAPlayer) Dunk() {
	fmt.Println(p.Name, "會扣籃")
}
Allen Iverson 從事的運動項目是打籃球
Allen Iverson 還會說唱
Allen Iverson 會扣籃

2.5* 空接口

空接口是指沒有定義任何方法的接口。因此任何類型都實現了空接口。”或許一切都是都是空接口“,空接口類型的變量可以存儲任意類型的變量。

2.5.1 空接口切片

  • 看一下fmt包的Println方法,參數就是一個空接口的切片
func Println(a ...interface{}) (n int, err error) {
	return Fprintln(os.Stdout, a...)
}

2.5.2 保存任意值的map

  • 我們定義map make(map[TKey]TValue),當TValue換成interface{}空接口時,這時候的mapvalue就不再是單一的類型,而是可以爲任意類型。
	var player = make(map[string]interface{})
	player["name"] = "LeBron James"
	player["age"] = 36

2.5.3 類型斷言

類型斷言主要用於判斷空接口中的值,因爲空接代表任意類型。x.(T)

var x interface{}
x = "randyfield"
v, ok := x.(string)
if ok {
    fmt.Println(v)
} else {
    fmt.Println("斷言失敗")
}

關於接口,不要爲了接口而寫接口,會增加不必要的抽象,導致不必要的運行時損耗。

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