Class skeleton

Learn the public class and static method structure.

What is public class?

In Java every source file must contain at least one class. A class is declared with the class keyword and must share the file name: a Main.java file holds public class Main.

The public modifier marks the class as accessible from outside. The class body sits between curly braces { } and contains methods and variables.

public class Main {
    // methods here
}

Only one public class may live in a file; other classes can be package-private.

The main method skeleton

The main method sits inside the class and is the entry point of a Java program. Its signature is always the same:

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

Four parts work together: public class Main is the shell, public static void main is the entry point, String[] args holds command-line parameters, and System.out.println is the output.

This skeleton is the basis of almost every Java program.

Exercise Complete the class skeleton

Define a Main class. Add a main method inside. From main, print Java 21 with println.

Show example solution

public class Main {
    public static void main(String[] args) {
        System.out.println("Java 21");
    }
}

Test yourself

Complete the class declaration

public ____ Main { }

Show answer

public class Main { }

Match the keywords

public

Accessible
class

Class declaration
static

Class-level
void

No return
What is the class naming convention?
- kebab-case (main-app)
- snake_case (main_app)
- PascalCase (MainApp)
- ALL_CAPS (MAIN_APP)
Show answer

PascalCase (MainApp) — Java classes use PascalCase.

Next lesson: javac and java

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