☕ Java Foundations · Beginner

Anatomy of a program in Java

Classes, the main method signature, braces, statements and semicolons.

🧩 The mysterypublic static void main(String[] args): that's a lot of ceremony just to say hi. Let's decode every piece.

The classic shape

Java code lives inside a class. Inside it, a method named main is where the program starts: the JVM finds it and runs its statements top to bottom.

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

Braces and semicolons

Braces { } group statements into a block: the class body, the method body. A statement is one instruction, like a println call, and every statement ends with ;. The semicolon is Java's full stop.

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

🔮 Predict it

Your turn

One character is missing. What happens?

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

Prints Hi
Compile error
Prints Hi with a warning

Show the answer

Compile error. The println line has no semicolon, so javac reports ';' expected and refuses to build the program.

Exactly main

The java launcher searches for a method named exactly main. Java is case-sensitive: a method called Main, start or run won't be found. (String[] args holds any words typed after the program name on the command line.)

Statements need a home

✗ Won't compile

public class Demo {
    System.out.println("Hi");
}

A class body can hold fields, methods, constructors and initializer blocks, but not bare statements.

✓ Works

public class Demo {
    public static void main(String[] a) {
        System.out.println("Hi");
    }
}

The statement lives inside a method.

🤔 Think first

Russian dolls

Order these from the outside in: method, statement, class, block.

Think about it, then reveal the answer

Class → method → block → statement. Classes contain methods, a method's body is a block, and blocks contain statements, each ending in ;.

💼 In the real world

In real projects

Your IDE flags a missing ; or brace instantly with a red squiggle. Knowing the anatomy lets you read the error fast: ';' expected or reached end of file while parsing tell you exactly which piece is missing.

Key takeaways

Code lives inside classes
Classic entry point: public static void main(String[] args)
Braces { } mark blocks; every statement ends with ;

🤯 Did you know?

main can also be written public static void main(String... args). The ... (varargs) form means the same as String[], and the launcher accepts it.

Practice questions

Which word completes the classic entry point?

public static void ___(String[] args) {
    System.out.println("Hi");
}

Main
main
start
run

Check your answer

main. The launcher looks for a method named exactly main. Java is case-sensitive, so Main is a different name.

Does this compile?

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

No: statements must be inside a method or initializer block
Yes, and it prints Hi when the class loads
Yes, but nothing is printed
Only if the class is not public

Check your answer

No: statements must be inside a method or initializer block. A class body can hold fields, methods, constructors and initializer blocks, but not bare statements like a println call.

Next: print, println, printf. Three ways to talk to the screen, and a separate channel just for errors.