• 2.2.1 Java Commands and Utilities
• 2.2.2 A first application
• 2.2.3 main

2.2 First Steps with Java

2.2.1 Java Commands and Utilities

• javac - the Java compiler
• java - the Java bytecode interpreter (JVM)
• appletviewer - lets you view applets without a browser
• jdb - the Java debugger
• javadoc - a utility that lets you generate documentation from your Java source code and the Javadoc comments you place in your source code
• jar - Java archive utility (similar to the Unix tar command)

2.2.2 A first application

• Assuming you have the JDK downloaded/installed, create a first Java application:

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

• Save the file as Hello.java.
• Compile the file to Java bytecode:

      javac Hello.java
  

• Run the program:

      java Hello
  

2.2.3 main

• When you run a Java application, the system locates and runs the main method for that class.
• The main method must be public, static, and void.
• The main method must accept a single argument of type String[].
• The arguments in the String array passed to main are program arguments, or command-line arguments.
• An application can have any number of main methods, because each class can have one.
• This is good, because each class can have a main method that tests it's own code.

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