First Java Program - Compile and Run HelloWorld

⏱️ 7 min read • Beginner Level • Lesson 7

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 learning how to write a Java program, you should read Java Program Structure. After this lesson, continue with Java Comments.

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.

Interview Questions ⭐

🧠 Test your understanding with a quick quiz

🎉 Great job! Continue learning Java step by step.