First Java Program – Compile and Run HelloWorld

⏱️ 7 min read • Beginner Level • Lesson 3

In this lesson, you will learn how to write, compile, and run your first Java program. We will create a simple HelloWorld.java file, compile it using the javac command, and execute it using the java command.

Before starting this lesson, make sure you have completed Java environment setup. If you are new to Java, you can also read Java introduction.

What You Need Before Writing Java Program

Steps to Write and Run a Java Program

1. Create the Source Code

Write your Java program in a text editor and save the file with the .java extension.

In this example, we will create a file named HelloWorld.java.

Example: HelloWorld.java

The following program prints Hello World on the screen:

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

2. Compile the Program

Open Command Prompt or terminal and go to the folder where your HelloWorld.java file is saved.

For example, if the file is saved on Desktop, use:

Change Directory

cd Desktop

Now compile the Java source file using:

Compile Command

javac HelloWorld.java

After successful compilation, a HelloWorld.class file is generated.

3. Run the Java Program

After compilation, run the program using the class name:

Run Command

java HelloWorld

Note: Do not include .class in the execution command. Use java HelloWorld, not java HelloWorld.class.

Explanation of HelloWorld Program

• public: access modifier that makes the class or method accessible from anywhere.
• class: keyword used to declare a class.
• HelloWorld: name of the class. The file name should be HelloWorld.java.
• static: allows the main method to run without creating an object.
• void: means the method does not return any value.
• main: entry point of the Java program.
• String[] args: stores command-line arguments.
• System.out.println(): prints output on the console.

Source Code Facts

• Java source code is written by the programmer.
• Java source files are saved with the .java extension.
• A Java source file may contain multiple classes.
• If a Java source file contains a public class, the file name must match the public class name.

package declaration;
import statements;

class ClassName {
    // class members
}   

Bytecode Facts

• The Java compiler generates bytecode after successful compilation.
• Bytecode is stored in a .class file.
• Bytecode is platform-independent.
• JVM interprets and runs bytecode.
• Each compiled Java class generates its own bytecode file.

🧠 Test your understanding with a quick quiz

🎉 Great job! Continue learning Java step by step.