Hello World Program in Java

Your first program

The classic first program in any language prints "Hello, World!". In Java it looks longer than in some languages, because every Java program must live inside a class and start from the main method. Let us write it and understand every part.

Step 0: install the JDK and check it

You need the JDK (Java Development Kit), not only the JRE, because it contains the compiler javac. Install a current LTS version (for example Java 21 or 25) from Eclipse Temurin (adoptium.net) or Oracle, then open a new Command Prompt/Terminal and check both tools:

java -version
javac -version

(Output from Java 21 on Linux; your version and build text will differ.)

If you see 'javac' is not recognized on Windows, the JDK bin folder is not in PATH. Re-run the installer with “Set JAVA_HOME / Add to PATH” ticked, or add C:\Program Files\Eclipse Adoptium\jdk-21…\bin to PATH and open a new window.

The Hello World code

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

Save this as Hello.java. It looks like a lot for one line of output, but each part has a clear job, which we break down next.

Line by line

• public class Hello — declares a class named Hello. The file must be Hello.java.
• public static void main(String[] args) — the starting point of the program.
• System.out.println("Hello, World!") — prints the text and moves to a new line.
• { } — curly braces group the code that belongs to the class and the method.

Everything you want the program to do goes inside main. When you run the program, Java looks for main and starts there.

Compile and run

javac Hello.java   // compile -> creates Hello.class
java Hello         // run (no .class)

javac turns your code into bytecode, and java Hello runs it. Notice you run java Hello, not java Hello.class.

Shortcut: run the source file directly

Since Java 11 you can run a single-file program without a separate compile step. Java compiles it in memory and runs it:

java Hello.java

This is perfect for practice programs. For exams and real projects still learn javac + java, because bigger programs have many files.

Real error messages and what they mean

These are the exact messages the Java 21 compiler printed when we made the most common beginner mistakes:

1. Missing semicolon

The number after the file name (:3) is the line. The caret ^ points where Java expected the ;.

2. File saved as hello.java (small h)

3. system instead of System

Java is case-sensitive: System is a class, system means nothing.

4. Main instead of main – compiles, but fails when run

Terminal, IDE or online compiler?

Newer Java: an even shorter Hello World

Java 25 added compact source files and instance main methods, so a beginner program can be written without the class line:

void main() {
    IO.println("Hello, World!");
}

It needs Java 25 or later. Most textbooks, CBSE/university practicals and interviews still use the classic public class … public static void main(String[] args) form, so learn that first.

print vs println

System.out.print("Hello ");
System.out.print("World");
System.out.println();          // new line
System.out.println("Next line");

print stays on the same line, while println moves to a new line after printing. Use println when you want each message on its own line.

Common mistakes

• File name mismatch. class Hello must be saved as Hello.java.
• Missing semicolon. Every statement ends with ;.
• Wrong main signature. It must be exactly public static void main(String[] args).
• Running with .class. Use java Hello, not java Hello.class.

Summary

• Every Java program lives in a class and starts from main.
• System.out.println prints a line of text.
• The file name must match the public class name.
• Compile with javac File.java, run with java File.
• print stays on the line; println moves to a new line.

Next, store data with Java variables, or set up your tools in the Java setup guide.