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Checking Installation in VS Code Terminal

Before writing your first program, it’s important to verify that Java has been installed correctly and that VS Code can detect it.
Open the VS Code integrated terminal and run:

java -version
javac -version

If everything is set up correctly, both commands will display version numbers. java refers to the Java Runtime, while javac refers to the Java Compiler.

Both commands must work.
If javac fails, your JDK is not properly installed or JAVA_HOME is not configured.

Creating Your First Java File

Every Java program begins with a .java file. Create a new file named:

Hello.java

A few important rules:

Every Java source file must end with .java
If your file contains a public class, the filename must match that class name

This is why we name the file Hello.java when our class is named Hello.

In Java, the filename and the public class name must match.
This helps the compiler organize and locate your code.

JShell (Interactive Mode)

JShell is Java's interactive REPL environment, introduced in Java 9. It allows you to quickly test small code snippets without creating files, compiling, or running a full program.

This makes JShell perfect for beginners experimenting with syntax or performing quick calculations.

Open JShell

jshell

Try basic expressions

2 + 3            // Output: 5
9 - 6            // Output: 3
print(6)         // Error
System.out.print(6)
System.out.println("Hello World")

Compiling and Running Code

Inside JShell, you can enter single lines of Java code. But to write real programs, you must place your code inside a class and compile it.

For example, this line works in JShell:

System.out.println("Hello World");

But placing only this line into Hello.java will cause an error.

If Hello.java contains only a print statement, it will fail to compile.
Java requires all code to be inside a class.

Compile the program

javac Hello.java

If the file is missing a class structure, the compiler will report errors and stop.

Minimal Working Java Program

Here is the simplest valid Java program you can write:

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

public class Hello defines the class
main() is the entry point — the first method executed by the JVM
System.out.println() prints output to the screen

Compile and run:

javac Hello.java
java Hello

If everything is correct, you should see:

Hello World

Congratulations — you have run your first Java program!

First Code