C#与Java编程语言之异同比较

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"论C#与Java之异同" 在计算机编程语言领域中，C#和Java是两种最为流行的对象 orientated 编程语言，它们都是基于虚拟机的平台，具有广泛的应用前景。然而，C#和Java之间存在着许多差异，本文将对C#和Java的异同进行详细的分析和比较。 **共同点** C#和Java都是基于对象 orientated 编程的语言，它们都支持面向对象的编程思想，包括封装、继承、多态等特性。同时，两种语言都支持垃圾回收机制，以减少内存泄露和提高程序的稳定性。此外，C#和Java都支持多线程编程，能够充分利用计算机的多核处理器，提高程序的执行效率。 **细微差异** 尽管C#和Java都支持面向对象的编程思想，但是它们在实现细节上存在着细微的差异。例如，C#使用的委托（Delegate）机制不同于Java的回调机制，C#的委托机制可以实现更加灵活的事件处理机制。同时，C#的属性（Property）机制不同于Java的Bean机制，C#的属性机制可以实现更加简洁的数据封装。 **概念差异** C#和Java在概念上也存在着一些差异。例如，C#的Async/Await机制不同于Java的Future机制，C#的Async/Await机制可以实现更加简洁的异步编程。同时，C#的 LINQ 机制不同于Java的Stream机制，C#的LINQ机制可以实现更加简洁的数据查询和处理。 **C#独有特性** C#有一些独有的特性，例如动态方法（Dynamic Method）和异步编程（Async/Await）机制，这些特性可以提高C#程序的执行效率和可读性。同时，C#的 attributes 机制可以实现更加灵活的元数据处理。 **Java独有特性** Java也有一些独有的特性，例如Java的泛型（Generic）机制不同于C#的泛型机制，Java的泛型机制可以实现更加灵活的类型参数化。同时，Java的Lambda表达式机制可以实现更加简洁的函数式编程。 **结论** C#和Java都是强大的对象 orientated 编程语言，它们都有着自己的优缺点。C#的强大之处在于其简洁的语法和强大的异步编程机制，而Java的强大之处在于其灵活的泛型机制和函数式编程机制。因此，在选择编程语言时，需要根据项目的需求和团队的经验来选择适合的语言。

static int num_created = 0;

int i = 0;

MyClass(){

i = ++num_created;

Console.WriteLine("Created object #" + i);

}

~MyClass(){

Console.WriteLine("Object #" + i + " is being finalized");

}

public static void Main(string[] args){

for(int i=0; i < 10000; i++)

new MyClass();

}

Java Code

public class MyClass {

static int num_created = 0;

int i = 0;

MyClass(){

i = ++num_created;

System.out.println("Created object #" + i);

}

public void finalize(){

System.out.println("Object #" + i + " is being finalized");

}

public static void main(String[] args){

for(int i=0; i < 10000; i++)

new MyClass();

}

6. Synchronizing Methods and Code Blocks

In Java it is possible to specify synchronized blocks of code that ensure that only one thread can access a particular object at a time and then create

a critical section of code. C# provides the

lock statement which is semantically identical to the synchronized statement in Java.

C# Code

public void WithdrawAmount(int num){

lock(this){

if(num < this.amount)

this.amount -= num;

}

Java Code

public void withdrawAmount(int num){

synchronized(this){

if(num < this.amount)

this.amount -= num;

}

Both C# and Java support the concept of synchronized methods. Whenever a synchronized method is called, the thread that called the method

locks the object that contains the method. Thus other threads cannot call a synchronized method on the same object until the object is unlocked by

the first thread when it finishes executing the synchronized method. Synchronized methods are marked in Java by using the

synchronized

keyword while in C# it is done by annotating the method with the

[MethodImpl(MethodImplOptions.Synchronized)] attribute. Examples of

synchronized methods are shown below

C# Code

using System;

using System.Runtime.CompilerServices;

public class BankAccount{

[MethodImpl(MethodImplOptions.Synchronized)]

public void WithdrawAmount(int num){

if(num < this.amount)

this.amount - num;

}

}//BankAccount

Java Code

public class BankAccount{

public synchronized void withdrawAmount(int num){

if(num < this.amount)

this.amount - num;

}

}//BankAccount

7. Access Modifiers

Below is a table mapping C# access modifiers to Java's. C++ fans who were disappointed when Sun changed the semantics of the protected

keyword in Java 2 will be happy to note that the C#

protected keyword has the same semantics as the C++ version. This means that a protected

member can only be accessed by member methods in that class or member methods in derived classes but is inaccessible to any other classes. The

internal modifier means that the member can be accessed from other classes in the same assembly as the class. The internal protected

modifier means that a member can be accessed from classes that are in the same assembly or from derived classes.

NOTE: The default accessibility of a C# field or method when no access modifier is specified is

private while in Java it is protected (except

that derived classes from outside the package cannot inherit the field).

Reflection

The ability to discover the methods and fields in a class as well as invoke methods in a class at runtime, typically called reflection, is a feature of

both Java and C#. The primary difference between reflection in Java versus reflection in C# is that reflection in C# is done at the assembly

level

while reflection in Java is done at the class level. Since assemblies are typically stored in DLLs, one needs the DLL containing the targeted class to

be available in C# while in Java one needs to be able to load the class file for the targeted class. The examples below which enumerate the

methods in a specified class should show the difference between reflection in C# and Java.

C# Code

using System;

using System.Xml;

using System.Reflection;

using System.IO;

class ReflectionSample {

public static void Main( string[] args){

Assembly assembly=null;

Type type=null;

XmlDocument doc=null;

try{

// Load the requested assembly and get the requested type

assembly = Assembly.LoadFrom("C:\\WINNT\\Microsoft.NET\\Framework\\v1.0.2914\\System.XML.dll");

type = assembly.GetType("System.Xml.XmlDocument", true);

//Unfortunately one cannot dynamically instantiate types via the Type object in C#.

doc = Activator.CreateInstance("System.Xml","System.Xml.XmlDocument").Unwrap() as XmlDocument;

if(doc != null)

Console.WriteLine(doc.GetType() + " was created at runtime");

else

Console.WriteLine("Could not dynamically create object at runtime");

}catch(FileNotFoundException){

Console.WriteLine("Could not load Assembly: system.xml.dll");

return;

}catch(TypeLoadException){

Console.WriteLine("Could not load Type: System.Xml.XmlDocument from assembly: system.xml.dll");

return;

}catch(MissingMethodException){

Console.WriteLine("Cannot find default constructor of " + type);

}catch(MemberAccessException){

C# access modifier Java access modifier

private private

public public

internal protected

protected N/A

internal protected N/A

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