Class and main method

Every standalone Java program starts in a class. The JVM looks for public static void main(String[] args) as the entry point—similar to how PHP scripts start at the top of a file, but Java requires an explicit method signature.

Minimal program structure

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

Public class name must match the filename. Save this as Main.java. A file cannot declare two public top-level classes.

Reading the main signature

• public — JVM can call it from outside the class
• static — runs without creating an instance of Main
• void — returns nothing
• String[] args — command-line arguments (often empty in the playground)

Important interview questions and answers

1. Q: Why must main be static?
   A: The JVM invokes main before any object exists; static methods belong to the class, not an instance.
2. Q: Can main be in any class?
   A: Yes, but conventionally in a class named after the app; the playground expects Main.
3. Q: What happens if the class name does not match the file?
   A: javac fails with a compile error.

Self-check

1. What three keywords appear before void main?
2. Why is the class named Main in this track?

Tip: The public class name must match the filename—Main.java requires public class Main. Fix that before debugging logic errors.