【持續更新】把.net代碼轉換為java代碼的注意事項，.netjava

【持續更新】把.net代碼轉換為java代碼的注意事項，.netjava

國內大多數大學的軟件相關專業大多強制學生學習c和Java，但.net 的幾個語言可以說是選學的。

由於visual studio在windows平台上使用相對方便，一些同學會在上大學的Java課之前自學.net開發技術。

這一類同學就需要一些代碼轉換技巧來幫助學習Java。

在這之前我吐槽一下TinyMCE編輯器，它不能正確染色一些vb.net的關鍵字，比如Async, NameOf, Aggregate 。c#的某些關鍵字也不能正確染色，如__arglist。

由於我這學期才開始上Java課，代碼中出現的錯誤歡迎大家指正。

1. 枚舉類型

VB

Public Enum Direction
    Right = 1
    DownRight
    Down
    DownLeft
    Left
    UpLeft
    Up
    UpRight
End Enum

C#

        public enum Direction
        {
            Down = 1,
            DownLeft,
            Left,
            UpLeft,
            Up,
            UpRight,
            Right,
            DownRight
        }

轉換成Java是這樣的。感覺跟c++/cli和c++/cx的enum class差不多。

如果原先的枚舉比較長，最好寫個小程序轉換一下。

public enum Direction {
            Down(1),
            DownLeft(2),
            Left(3),
            UpLeft(4),
            Up(5),
            UpRight(6),
            Right(7),
            DownRight(8)

    private int __value;

    private Direction(int value) {
        this.__value = value;
    }

    @Override
    public String toString() {
        return String.valueOf(this.nCode);
    }

}

那個__value是我抄.net參考源碼的，如果看不順眼可以改名。

2.異常

Java的異常如果不是RuntimeException這一類的，就得用Throws 聲明，否則像AccessViolationException這一類錯誤一樣只能在UnhandledException（ErrorListener）那裡處理。

轉換代碼的時候寫一堆Throws比較麻煩，寫了一層就忘了下面那一層有什麼異常了。

這個比較好辦，只要不是致命的異常，那自定義異常就都繼承RuntimeException好了。自帶的幾個需要用Throws的異常用ErrorListener攔截。

class PointOutOfScreenException extends RuntimeException{
    public PointOutOfScreenException(){
        super("點出屏幕了...");
    }
}

3.標識符類型的推斷

VB

Dim a = New StringBuilder

C#

var a = new StringBuilder();

轉換成Java就用復制粘貼大法，把類名復制一下然後粘貼到開頭

StringBuilder a = new StringBuilder();

4. c#不安全模式, vb和f#各種調運行庫的獨有運算符, 動態, async, await, linq, 無符號類型 .......

VB

        Async Function LoadImages(device As CanvasDevice) As Task
            forestTiles = Await SpriteSheet.LoadAsync(device, $"SpriteSheets/ForestTiles{NameOf(ImageID)}.png", New Vector2(64, 64), Vector2.Zero)
            wizardWalk = Await SpriteSheet.LoadAsync(device, "SpriteSheets/WizardWalkRight.png", New Vector2(128, 192), New Vector2(64, 150))
            wizardIdle = Await SpriteSheet.LoadAsync(device, "SpriteSheets/WizardIdleRight.png", New Vector2(128, 192), New Vector2(64, 150))
        End Function

C#

        async Task LoadImages(CanvasDevice device)
        {
            forestTiles = await SpriteSheet.LoadAsync(device, $"SpriteSheets/ForestTiles{nameof(ImageID)}.png", new Vector2(64, 64), Vector2.Zero);
            wizardWalk = await SpriteSheet.LoadAsync(device, "SpriteSheets/WizardWalkRight.png", new Vector2(128, 192), new Vector2(64, 150));
            wizardIdle = await SpriteSheet.LoadAsync(device, "SpriteSheets/WizardIdleRight.png", new Vector2(128, 192), new Vector2(64, 150));
        }

VB

    Public Function CalculateClipGeometry(resource As ICanvasResourceCreator, SourcePoint As Vector2, Geometies As CanvasGeometry(), ScreenSize As Size) As CanvasGeometry
        Dim geos = Aggregate geo In Geometies
                       Let Lines = Aggregate tes In geo.Tessellate
                                   From ln In {New LineSegment(tes.Vertex1, tes.Vertex2), New LineSegment(tes.Vertex1, tes.Vertex3), New LineSegment(tes.Vertex3, tes.Vertex2)}
                                   Select ln Distinct Into ToArray
                       Select Rays = Aggregate tes In geo.Tessellate
                           From light In {New LineSegment(SourcePoint, tes.Vertex1), New LineSegment(SourcePoint, tes.Vertex2), New LineSegment(SourcePoint, tes.Vertex3)}
                               Where Not (Aggregate l In Lines Where light.RayToBoundary(ScreenSize).HasIntersection(l) Into Any)
                           Select light
                       Into ToArray
                       Where Rays.Length >= 2 AndAlso Rays(0).Name Like "Ln*"
                       Let Fir = Rays.First
                       Select Arr = Aggregate ln In Rays Order By ln.Angle(Fir) Into ToArray
                       Select CanvasGeometry.CreatePolygon(resource, {Arr.First.Point2, Arr.First.RayToBoundary(ScreenSize).Point2, Arr.Last.RayToBoundary(ScreenSize).Point2, Arr.Last.Point2})
                   Into ToArray
        Return geos.Union
    End Function

C#

 public unsafe void AddThree(__arglist)
 {
    var args = new ArgIterator(__arglist);
    var a = (byte*)TypedReference.ToObject(args.GetNextArg());
    *a+=3;
 }

Java

// TODO: 自己重新寫吧。直接轉換這種代碼反而浪費時間！

我還要上課呢，這次就寫到這裡吧。喜歡Java的可以找出描述不合理的地方，但是請勿噴。