Write Your First Java Program

Create a file named HelloWorld.java. In Java, the source filename must match the name of a public top-level class.

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

Understand the code#

• public class HelloWorld declares a class named HelloWorld.
• main is the standard entry point used to start this simple application.
• System.out.println(...) prints text followed by a new line.
• The braces {} mark the start and end of code blocks.
• The semicolon ; ends each statement.

Compile and run it#

Open a terminal in the directory containing the file. Run these commands in order:

javac HelloWorld.java
java HelloWorld

The first command creates HelloWorld.class if compilation succeeds. The second starts the class; do not add .class to the command.

Expected output:

Hello, Java!

Common beginner errors#

• Filename mismatch: save the public class as HelloWorld.java.
• Missing semicolon: Java statements such as the print statement need a semicolon.
• Wrong directory: run the commands in the directory containing the source file, or provide the correct path.
• Using java HelloWorld.java in a compile-first workflow: for this course, compile with javac first and run the class name with java.

Practice#

Change the text to your name and compile the program again. Then print two lines using two System.out.println statements.