The main() Method

The Big Picture

main is the single entry point the JVM calls to start your program. The classic signature must match this form or the JVM won't find it.

• public - reachable from outside the class (the JVM calls it)
• static - runs without creating an object first
• void returns nothing · String[] args carries command-line input

How It Works

The java launcher loads your class, then the JVM invokes main on the "main" thread. Tokens typed after the class name become args.

• java Greet Alice Bob → args = {"Alice", "Bob"}
• Every element is a String - parse numbers with Integer.parseInt
• The shell splits on spaces; quote to keep a token together

In the Java Landscape

The classic form is stable, but a few variants are worth knowing.

• String... args (varargs) is an equally valid signature
• System.exit(int) sets the process exit code (0 = success)
• Java 25 finalizes a simpler instance main + compact source files

(preview in Java 21-24) - the classic form still works everywhere

Pitfalls and Best Practices

• A signature typo → "Main method not found" - the JVM won't start
• args is never null but can be empty - guard args.length
• Reading args[0] with no input → ArrayIndexOutOfBoundsException
• Keep main thin - delegate real logic to other methods/classes