Java

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Hello World (Applet)

Michael Neumann

import java.applet.*;
import java.awt.*;

public class HelloWorld extends Applet {
   public void paint(Graphics g) {
      g.drawString("Hello World",10,10);
   }
}

Prints "Hello World" onto the screen.

Hello World (Application)

Michael Neumann

public class HelloWorld {
   public static void main(String[] args) {
      System.out.println("Hello World");
   }
}

Prints "Hello World" onto the screen.

Hello World (Servlet)

Michael Neumann

/*
 * Hello World in Java (Servlet)
 */ 

import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;

public class HelloWorld extends HttpServlet
{
  public void doGet (HttpServletRequest request, HttpServletResponse response)
    throws ServletException, IOException
  {
    PrintWriter out;
    String text = "Hello World in Java (Servlet)";
    
    response.setContentType("text/html");
    out = response.getWriter();
            
    out.println("<html><head><title>");
    out.println(text);
    out.println("</title></head><body>");
    out.println(text);
    out.println("</body></html>");

    out.close();
  }
}

Prints "Hello World" onto the screen.

Hello World (Swing-GUI)

Michael Neumann

import javax.swing.*;

class HelloWorldSwing {

  public static void main(String args[]) {
    JFrame mainWin = new JFrame("MainWindow");
    JButton button = new JButton("Hello World");
    mainWin.getContentPane().add(button);
    mainWin.pack();
    mainWin.show();
  }

}

Prints "Hello World" onto the screen.

Multi-threading

Michael Neumann

public class ThreadTest implements Runnable {
  public static void main(String args[]) {
    int i, j;

    // create 1000 threads
    for (i=0; i<=1000; i++) {
      Thread th = new Thread(new ThreadTest());
      th.start();
    }

    // do some calculation
    for(i=j=0; i<=100000; i++) {
      j = j + i;
    }
  }

  public void run() {
    try {
      // sleep forever
      Thread.currentThread().sleep(1000000);
    } catch (InterruptedException e) {}
  }
}

Create 1000 threads that sleep.