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For this book you will use Notepad to enter your application. To do this enter the command:

notepad HelloWorld.java

Make sure you enter this exactly as I have it. If you change which letters are capital, you will run into problems! This will start up Notepad and allow you to enter your source code. The source code is what makes up your program and is compiled into your final application. Once you enter the above command you will see Notepad launch and ask if you want to create a new file. You should choose “Yes”, as seen in Figure 2.20.

Figure 2.20: Create your Source Code

If you use notepad to re-open this file later, you will not be prompted to create the file, the file will simply open. Now that Notepad is open you should enter the application as seen in Figure 2.21.

Figure 2.21: Enter your Source Code

This program is shown in Listing 2.1.

Listing 2.1: Hello World! (HelloWorld.java)

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

Once you have entered your program you will compile it, as shown in the next section.

One very important item to note is the class name. The class name above, in Listing 2.1, is HelloWorld. This must match the filename
“HelloWorld.java”.