Compile and run

javac, java, and the modern single-file launch.

From source to output

The classic two-step build:

javac Hello.java     # compile  → produces Hello.class
java Hello           # run      → JVM executes Hello.class

Note you run java Hello — the class name, with no .class extension and no path tricks. The JVM finds Hello.class on the classpath and invokes its main.

Since Java 11 there's a shortcut for quick programs — launch a single source file directly, compiling it in memory:

java Hello.java

Great for learning and scripts. For anything bigger you'll use a build tool (Maven or Gradle), which we cover later — but underneath, it's still javac then java.