The Hello World Program

In this section, you will learn to write the Hello World program.

Many programming books begin with a simple example program that prints the text, “Hello, world!” on the console.

public class Hello {

    public static void main(String... arguments) {
        System.out.println("Hello, world!");
    }
}
  • Copy the source code from here.
  • Paste the source code into a text editor, such as Notepad or Notepad++.
  • Save it in a file named Hello.java.
  • You need to remember where you save your file. In our example, I have saved it in C:\examples\chapter-3.
  • Open a console window.
  • Change the current working directory to the directory where your file is saved. In our example, it is C:\examples\chapter-3.

  • To change the current working directory use the cd command. For example,

    cd C:\examples\chapter-3

  • Compile it with javac Hello.java in the console window.

  • Run your program with java Hello in the console window.

Opening Console Window on Windows

Method 1

  1. Press the Windows + R keys.
  2. A dialog with the title Run will appear on the screen.
  3. Type cmd in the text field.
  4. Press enter.

Method 2

  1. Click on the Windows logo in the bottom left corner of your screen.
  2. Search cmd.exe in the search field.

  3. Click on cmd.exe.

    public class Hello {

Here you created a class called Hello. It is public, which means other classes can access it. You don’t have to know what this means for now, so don’t worry. You will learn about access specifiers later in the book.

When you declare a public class, you must always save it inside a file with the same name. In our first example, our class was named Hello. So, it was saved in the file Hello.java.

The opening brace { begins the body of the class. The end of the body is marked by the closing brace }. Whatever you declare within these braces belongs to the class.

    public static void main(String[] arguments) {

Here you created a method called main. You don’t have to know what this means for now, so don’t worry. You will learn more about methods later in the book.

The main method is the entry point of your Java program. In other words, your program always starts at main.

When you declare a public method, other classes can access it. You will learn more about access specifiers later in the book.

You can call a static method without creating an instance of Hello. You will learn more about static later in the book.

(String[] arguments) is too advanced to explain just yet. It’s called a parameter list. You can use it to pass data to a method.

The main method always receives a single parameter: an array of String objects. If you don’t know what a parameter, a String, or an array is, don’t worry. You will learn more about these concepts later in the book.

The opening brace { begins the body of the method. The end of the method is marked by the closing brace }. Whatever statements you write within these braces are executed when you call the method.

        System.out.println("Hello, World!");

System is a class that Java provides us. It has some useful methods and variables. out is a static variable within System. println is a method within out. You can call it to write data on your console window.