MyFirstJavaProgram

Java Quickstart

In Java, every application begins with a class name, and that class must match the filename.

Let's create our first Java file, called MyFirstJavaProgram.java, which can be done in any text editor (like Notepad).

The file should contain a "Hello World" message, which is written with the following code:

MyFirstJavaProgram.java

Let's start.....

Public class MyFirstJavaProgram {
 /* This is my first java program.
  * This will print 'Hello World' as the output
  */
    public static void main(String[] args) {
    System.out.println(“Hello World”);
   }
}

Don't worry if you don't understand the code above - we will discuss it in detail in later chapters. For now, focus on how to run the code above.

Save the code in Notepad as "MyFirstJavaProgram.java". Open Command Prompt (cmd.exe), navigate to the directory where you saved your file, and type "javac MyFirstJavaProgram.java":

C:\Users\Your Name>javac MyFirstJavaProgram.java

This will compile your code. If there are no errors in the code, the command prompt will take you to the next line. Now, type "java MyFirstJavaProgram" to run the file:

C:\Users\Your Name>java MyFirstJavaProgram

The output should read:

Hello World

Congratulations! You have written and executed your first Java program.

In the previous chapter, we created a Java file called MyFirstJavaProgram.java, and we used the following code to print "Hello World" to the screen:

MyFirstJavaProgram.java

public class MyFirstJavaProgram {

  public static void main(String[] args) {

    System.out.println(“Hello World”);

  }

}

Example explained

Every line of code that runs in Java must be inside a class. In our example, we named the class MyFirstJavaProgram. A class should always start with an uppercase first letter.

Note: Java is case-sensitive: "MyFirstJavaProgram" and "myfirstjavaprogram" has different meaning.

The name of the java file must match the class name. When saving the file, save it using the class name and add ".java" to the end of the filename.The output should be:

Hello World

 The main Method

The main() method is required and you will see it in every Java program:

public static void main(String[] args)

Any code inside the main() method will be executed. You don't have to understand the keywords before and after main. You will get to know them bit by bit while reading this tutorial.

For now, just remember that every Java program has a class name which must match the filename, and that every program must contain the main() method.

System.out.println()

Inside the main() method, we can use the println() method to print a line of text to the screen:

public static void main(String[] args) {

  System.out.println(“Hello World”);

}

Note: 1) The curly braces {} marks the beginning and the end of a block of code.
2) Each code statement must end with a semicolon.