【持续更新】把.net代码转换为java代码的注意事项

国内大多数大学的软件相关专业大多强制学生学习c和Java，但.net 的几个语言可以说是选学的。

由于visual studio在windows平台上使用相对方便，一些同学会在上大学的Java课之前自学.net开发技术。

这一类同学就需要一些代码转换技巧来帮助学习Java。

转载请说明作者Nukepayload2

在这之前我吐槽一下TinyMCE编辑器，它不能正确染色一些vb.net的关键字，比如Async, NameOf, Aggregate 。c#的某些关键字也不能正确染色，如__arglist。

由于我这学期才开始上Java课，代码中出现的错误欢迎大家指正。

1. 枚举类型

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
        }

转换成Java是这样的。感觉跟c++/cli和c++/cx的enum class差不多。

如果原先的枚举比较长，最好写个小程序转换一下。

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);
    }

}

那个__value是我抄.net参考源码的，如果看不顺眼可以改名。

2.异常

Java的异常如果不是RuntimeException这一类的，就得用Throws 声明，否则像AccessViolationException这一类错误一样只能在UnhandledException（ErrorListener）那里处理。

转换代码的时候写一堆Throws比较麻烦，写了一层就忘了下面那一层有什么异常了。

这个比较好办，只要不是致命的异常，那自定义异常就都继承RuntimeException好了。自带的几个需要用Throws的异常用ErrorListener拦截。

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

 

3.标识符类型的推断

VB

Dim a = New StringBuilder

C#

var a = new StringBuilder();

转换成Java就用复制粘贴大法，把类名复制一下然后粘贴到开头

StringBuilder a = new StringBuilder();

4. c#不安全模式, vb和f#各种调运行库的独有运算符, 动态, async, await, linq, 无符号类型 .......

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: 自己重新写吧。直接转换这种代码反而浪费时间！

 

5.事件和委托

遇到这个没有第四条那么极端，因为Java有用于实现接口的匿名类。

VB

Event Slide(sender As Object, e As SlideEventArgs)

C#

delegate void SlideEventHandler(object sender, SlideEventArgs e);
event SlideEventHandler Slide;

Java

interface SlideEventHandler{
    void slide(Object sender, SlideEventArgs e);
}

 VB 处理事件

Sub xx_Slide(sender As Object, e As SlideEventArgs) Handles xx.Slide
...
End Sub

C# 处理事件

类名()
{
    xx.Slide += xx_Slide;
}
void xx_Slide(object sender, SlideEventArgs e)
{
...
}

VB 使用Lambda表达式处理事件

AddHandler xx.Slide, Sub(sender, e) ...

C# 使用Lambda表达式处理事件

xx.Slide += (sender, e) =>  ...  ;

Java 处理事件

xx.setSlideListener(new SlideEventHandler(){
    void slide(Object sender, SlideEventArgs e){
        ...
    }
});

我现在还没看JDK 1.8的Lambda表达式能不能用来处理事件和完成委托，所以不提供这方面的Java代码。

 

我还要上课呢，这次就写到这里吧。喜欢Java的可以找出描述不合理的地方，但是请勿喷。