Contrasting C# and Java Syntax(摘录)

http://www.ondotnet.com/pub/a/dotnet/2001/06/14/csharp_4_java.html

1. 简单类型

C#中的primitive type也是object的子类，因此可以直接调用ToString 或 GetType。

  如Int是System.Int32的假名，后者继承了System.Object

注意：C#中简单类型仍然是pass-by-value

 2. 常量定义
Java：static final
C#：

const int TWO = 2;

              the keyword “readonly”(在声明处或构造函数中可以赋值，可以是动态赋值)

3. switch语句中的差异

C#中不允许fall-through, 否则会有编译错误。

In C#, an explicit break or goto case to a different case is required somewhere in the case to explicitly define the control flow.

如

       switch(n)
        {
        case 1:

            cost += 25;

            break;

        case 2:

            cost += 25;

            goto case 1;

4.特有的循环语句 foreach
实现了System.Collections.IEnumerable 接口的object都可以使用foreach, 如array.

5.C#中，所有的异常都是run-time exceptions; 都继承了System.Exception.

6. 函数参数修饰符: params, ref, out

(1) params（其实只是为了简化把数组作为函数参数的过程）

       方法的最后一个参数如果是数组，可以在这个参数前加params关键词。

public void methodCaller( params int[] a );

and the method can be called with any of

methodCaller( 1 );

methodCaller( 1, 2, 3, 4, 5 );

Inside methodCaller, the parameters can be accessed through the "a" array defined.

7. Property(对应于Java class里的一个属性及getter/setter)

定义

private int property;

public int Property {

  get {

    return this.property;

  }

  set {

    // value is an implicit variable generated by the

    //  compiler to represent the parameter

    this.property = value;

  }

}

使用

int currentValue = Property;

Property = newValue;

8. Extra Accessibility Modifier
internal - this is a new one to Java programmers, as this means that a member is accessible from the entire assembly. All the objects you define inside a .cs file (you can define more than one object inside the .cs file, unlike Java, where you can usually define only one object) have a handle to the internal member.

 protected internal - think of this one as the union of protected and internal, as the item is is modifying is either protected or internal. This item can be accessed from the entire assembly, or within objects which derive from this class.

 9. C#中的类继承语法

class D : B, C {

// B,C可以是class，也可以时interface；如果是一个是class，一个是interface，class要放在interface前面。

 }

 10 C#中的Struct

    * structs are passed by value instead of by reference

    * structs cannot extend anything (nor can anything extend them) -- they may, however, implement interfaces

    * structs may not define a constructor with no parameters

    * structs that define constructors with parameters must explicitly define all fields before they return control to the caller

 11. C#中的base对应Java中的super

 12. Overriding Methods

 All methods in an object are "final" (in the Java sense of the word) by default. In order for a method to be overridden by an inheriting object, the original method needs to be marked "virtual" and all methods overriding the virtual method in the inherited classes must be marked "override." For example:

 public class A : Object {

  public virtual void toOverride() { }

 }

 public class B : A {

  public override void toOverride() { }

 }

 is required in C# for the compiler not to complain when defining the inheriting class.

 13. 类型转换

public class FloorDouble : Object {

  private double value;

   public FloorDouble( double value ) {

    this.value = Math.Floor( value );

  }

   public double Value {

    get {

      return this.value;

    }
  }

   public static explicit operator FloorDouble( double value ) {

    return new FloorDouble( value );

  }

   public static implicit operator double( FloorDouble value ) {

    return value.Value;

  }

}

 // this class can be used by

FloorDouble fl = (FloorDouble)10.5

double d = fl;

 14 操作符重载

 15. C#里的namespace

    (1) 不能引入单独的一个类

       (2) alias for long namespace

using short = a.really.long.namespace.theClass;

       (3)不与文件系统中的结构对应