Command-Line Java Execution: From JDK 8 to JDK 22

For beginners who install IntelliJ IDEA and want to run a simple "Hello World" program, the usual workflow involves creating a Java source file, compiling it with javac , and then executing the resulting class with java . The article walks through this process step by step.

First, a minimal class Moon.java is shown:

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

On JDK 8 you must compile the file:

javac Moon.java

and then run it with an explicit class‑path:

java -classpath . Moon

If the program references another class, e.g. Helper.java , both files need to be compiled together:

javac Moon.java Helper.java

and executed the same way:

java -classpath . Moon

Starting with JDK 11 the launcher supports running a single source file directly, so the compilation step can be omitted:

java Moon.java

However, when multiple source files are involved (e.g., Moon.java calling Helper.sayHello() ), the old compile‑then‑run sequence is still required.

JDK 22 introduces an enhanced source‑file mode that allows a program consisting of several Java files to be launched directly:

java Moon.java

This eliminates the need for an explicit compilation step for multi‑file projects, making the command‑line experience similar to interpreted languages like Python.