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J# Versus Java, Example by Example

Let's examine some programs using different languages and test whether the same CLR would support them. In other words, if the same environment can understand multiple languages at runtime, it supports cross-language development.

I've chosen four categories of examples to demonstrate how elegantly this new tool from Microsoft works:

  • Command-line examples
  • Cross-language examples
  • Windows forms examples
  • Web services examples

I'll demonstrate all the examples based on the following approach:

  • How the program looks in Java
  • How the program looks in J#
  • How the program looks in .NET

NOTE

To maintain uniformity across all programs written using different languages, I've used import System.*; in Java programs, though it's essentially not required.

Command-Line Examples

Take a look at the following simple Java program, which outputs a simple string to the command prompt. There is nothing special in this program.

Java Example

//To Compile - javac welCome.java
//To Run - java welCome
import System.*;
class welCome
{
public static void main(String[] args)
{
System.out.println("Welcome To .NET Technology Group - PCS");
}
}

Now examine the same program written using J#. This program looks much like the Java program except for the extension and the compiler; here we use JC instead of JAVAC.

J# Example

//To Compile - jc welCome.jsl
//To Run - welCome
import System.*;
public class welCome
{
public static void main(System.String[] args)
{
System.out.println("Welcome To .NET Technology Group - PCS");
}
}

Now look at the following version. I've changed the file extension to .java but still use the JC compiler instead of JAVAC. The code we compile gets converted to Intermediate Language rather than to Java bytecode. If you're programming for the first time in the .NET world, this is a big surprise. However, if you've worked on other .NET compilers, you might have observed that you needn't bother about the extensions of the filenames; instead, you just look at the code for a given file. That's the reason we can compile with both extensions—.java as well as .jsl. In fact, you can save your files with any extension.

//To Compile - jc welCome.java
//To Run - welCome
import System.*;
public class welCome
{
public static void main(System.String[] args)
{
System.out.println("Welcome To .NET Technology Group - PCS");
}
}

In the next version, notice that I've changed the output function—from System.out.println() to System.Console.WriteLine(). As mentioned earlier, under the .NET Framework all languages use a common library, the Base Class Library (BCL). Since this compiler targets CLR, it's expected to acquire the same capability.

.NET Example

//To Compile - jc welCome.jsl
//To Run - welCome
import System.*;
public class welCome
{
public static void main(System.String[] args)
{
System.Console.WriteLine("Welcome To .NET Technology Group - PCS");
}
}

The following table compares the programs so far.

 

Java Program

J#/.NET Program

File extension

.java

Any extension; .jsl by default

Compiler

JAVAC

JC

Library functions

Java API

Java API and .NET Framework library

Intermediate form

Java bytecode

Intermediate Language (IL)

Runtime environment

JVM (Java Virtual Machine)

CLR ( Common Language Runtime)

Platform

Can run on multiple platforms

Designed to run on multiple platforms

Interoperability with other languages

Lacks cross language capabilities to a great extent

Sound cross-language capabilities

Output

Filename.class

Filename.exe or Filename.dll

Documentation

HTML

XML


Cross-Language Examples

This particular feature is unique to CLR. By cross-language capability, I mean that a method written in one language can be overridden in another language and so on. Exception handling across different languages could be achieved.

Though Java has limited capability to interoperate with certain languages like Smalltalk, it has never attained full-blown cross-language capabilities. The reason could be simply that Java was never designed to attain such a capability.

Java to C#

The following examples implement a getMessage() method in the J# program, inherit it in the C# program, and override it with another implementation. The following program generates a DLL, namely welCome.dll.

//jc /t:library welCome.jsl
import System.*;
public class welCome
{
 public void getMessage()
 {
 System.Console.WriteLine("Welcome To .NET Technology Group - PCS");
 }
}

The following program uses the welCome.dll created in the program above, inherits the getMessage() method, and overrides this program with new implementation. It works amazingly well to enable Java programmers to inherit the code written other languages and use it in their programs.

//csc /r:welCome.dll, BJLIB.dll demoWelCome.txt
using System;
class demoWelCome:welCome
{
  public static void Main()
  {
   demoWelCome t = new demoWelCome();
   welCome w = new welCome();
   t.getMessage();
   w.getMessage();
  }
  public override void getMessage()
  {
   Console.WriteLine("Cross-Language Capabilities of .NET");
  }
}

Java to Java

The following code is written in Java with the getMessage () method. This feature wouldn't work in Java.

//To Compile - Javac welCome
import System.*;
public class welCome
{
   public void getMessage()
   {
     System.out.println("Welcome To .NET Technology Group");
   }
}

In the following example, we will try to inherit the welCome class and override the getMessage() of the welCome class with a new implementation. Of course, in this case, we will be able to accomplish this only within a single language.

// To Compile - Javac demoWelCome
// To Run - Java demoWelCome
import System.*;
class demoWelCome extends welCome
{
  public static void main(String[] args)
  {
   demoWelCome t = new demoWelCome();
   welCome w = new welCome();
   t.getMessage();
   w.getMessage();
  }
  public void getMessage()
  {
  System.out.println("Cross-Language Capabilities of .NET - PCS");
  }
}

C# to Java

The earlier examples showed you how to take a method written in Java and override it in C# to create a new implementation. But there might be situations where we would like to reverse this process. In the following program, the getMessage() method is implemented using C# and then overridden in J#/Java.

//To Compile - csc /t:library welCome
using System;
public class welCome
{
   public void getMessage()
   {
     System.out.println("Welcome To .NET Technology Group");
   }
}

The following example overrides the getMessage() and implements it as I wish. This probably surprises many Java programmers, thanks to such a nice cross-language environment.

//jc /r:welCome.dll demoWelCome.jsl
import System.*;
class demoWelCome extends welCome
{
  public static void main(System.String[] args)
  {
   demoWelCome t = new demoWelCome();
   welCome w = new welCome();
   t.getMessage();
   w.getMessage();
  }
  public void getMessage()
  {
   System.out.println("Cross-Language Capabilities of .NET");
  }
}

The .NET Way

The following program shows you how this is implemented in a strict .NET Framework.

//To Compile - csc /t:library welCome
using System;
public class welCome
{
   public void getMessage()
   {
     System.Console.WriteLine("Welcome To .NET Technology Group");
   }
}

In the following example, we will try to inherit the welCome class within J# itself. Later, we will also try to override the getMessage() method.

//jc /r:welCome.dll demoWelCome.jsl
import System.*;
class demoWelCome extends welCome
{
  public static void main(System.String[] args)
  {
   demoWelCome t = new demoWelCome();
   welCome w = new welCome();
   t.getMessage();
   w.getMessage();
  }
  public override void getMessage()
  {
   Console.WriteLine("Cross-Language Capabilities of .NET");
  }
}

The following table compares the programs.

 

Java Program

J#/.NET Program

Override Keyword

Not necessary

Optional

Library Function

System.out.println

System.Console.WriteLine

Overriding

Java compiler gives no warning

J# compiler gives a warning


Windows Forms

Now let's move ahead to build some GUI applications. Here we'll examine the examples written using pure J#, Java AWT, and Java Swing.

The following example is written using AWT of Java-like code but targets for CLR rather than JVM. The program looks exactly like a pure Java AWT program. But if you observe the code closely you find that I've saved the file with a .jsl extension. It doesn't matter even if I save it with a .class extension. I compiled without any errors and can run it successfully.

Windows Forms

//To Compile - jc AWTTest.jsl
// To Run - AWTTest
import java.awt.*;
import java.awt.event.*;
public class AWTTest extends Frame implements WindowListener{
  public AWTTest() {
   this.setTitle("Welcome To .NET Technology Group");
   this.setSize(400,300);
   this.addWindowListener(this);
   this.setBackground(Color.white);
   this.setVisible(true);
  }
  public void windowClosing(WindowEvent we){
   System.exit(0);
  }
  public void windowOpened(WindowEvent we){}
  public void windowClosed(WindowEvent we){}
  public void windowIconified(WindowEvent we){}
  public void windowDeiconified(WindowEvent we){}
  public void windowActivated(WindowEvent we){}
  public void windowDeactivated(WindowEvent we){}
  public static void main(String[] args){
   AWTTest obj = new AWTTest();
  }
}

Java AWT

Here's a simple Java AWT program that displays a window.

//To Compile - javac AWTTest.java
//To Run - java AWTTest
import java.awt.*;
import java.awt.event.*;
public class AWTTest extends Frame implements WindowListener{
  public AWTTest() {
   this.setTitle("Welcome To .NET Technology Group");
   this.setSize(400,300);
   this.addWindowListener(this);
   this.setBackground(Color.white);
   this.setVisible(true);
  }
  public void windowClosing(WindowEvent we){
   System.exit(0);
  }
  public void windowOpened(WindowEvent we){}
  public void windowClosed(WindowEvent we){}
  public void windowIconified(WindowEvent we){}
  public void windowDeiconified(WindowEvent we){}
  public void windowActivated(WindowEvent we){}
  public void windowDeactivated(WindowEvent we){}
  public static void main(String[] args){
   AWTTest obj = new AWTTest();
  }
}

Java Swing

Here I've used Swing rather than AWT, just to show how you can implement the same program using Swing.

//To Compile - javac SwingTest
//To Run - java SwingTest
import javax.swing.*;
import java.awt.event.*;
import java.awt.*;
public class SwingTest extends JFrame implements WindowListener{
  Container cnt = null;
  public SwingTest() {
   cnt = this.getContentPane();
   this.setTitle("Welcome To .NET Technology Group");
   this.setSize(400,300);
   this.addWindowListener(this);
   cnt.setBackground(Color.white);
   this.setVisible(true);
  }
  public void windowClosing(WindowEvent we){
   System.exit(0);
  }
  public void windowOpened(WindowEvent we){}
  public void windowClosed(WindowEvent we){}
  public void windowIconified(WindowEvent we){}
  public void windowDeiconified(WindowEvent we){}
  public void windowActivated(WindowEvent we){}
  public void windowDeactivated(WindowEvent we){}
  public static void main(String[] args){
   SwingTest obj = new SwingTest();
  }
}

The .NET Way - Pure J#

The following program uses the .NET Framework Base Class Library and Java-like syntax. This feature is common to all .NET languages, no matter what language you use for writing applications.

//jc /r:System.Windows.Forms.dll,System.Drawing.dll welCome.jsl
import System.Drawing.*;
import System.ComponentModel.*;
import System.Windows.Forms.*;
public class welCome extends System.Windows.Forms.Form
{
  private System.ComponentModel.Container components = null;
  public welCome()
  {
   
   InitializeComponent();
   
  }
  protected void Dispose(boolean disposing)
  {
   if (disposing)
   {
     if (components != null)
     {
      components.Dispose();
     }
   }
   super.Dispose(disposing);
  }
  private void InitializeComponent()
  {
   this.components = new System.ComponentModel.Container();
   this.set_Size(new System.Drawing.Size(300,300));
   this.set_Text("Welcome To .NET Technology Group");
  }
  public static void main(String[] args)
  {
   Application.Run(new welCome());
  }
}

The following table compares the programs.

 

Java Program

J#/.NET Program

AWT Support

Full support

Limited support

Swing

Full support

No support


Web Services

Web services are relatively new to most Java programmers. Designing web services using .NET is fairly easy and simple. Though it requires manual generation of web services proxy class, in beta 1 of J# you can write both service and client very easily.

The following code shows how simple it is to write a web service using J#, using the welCome.asmx file of ASP.NET applications.

import System.Collections.*;
import System.ComponentModel.*;
import System.Data.*;
import System.Diagnostics.*;
import System.Web.*;
import System.Web.Services.*;
public class welCome extends System.Web.Services.WebService
{
  public welCome()
  {
   InitializeComponent();
  }
  
  private void InitializeComponent()
  {
  }
  public void Dispose()
  {
  }
  
  public System.String getMessage(String helloMsg)
  {
   return helloMsg;
  }
}
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