Java Syntax, Output and Comments

Every Java program follows a few simple rules. Learn them once and you will read any Java code more easily.

The Structure of a Program

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

The example explained

Java Syntax Rules

• Java is case sensitive: Main and main are different names
• Every statement ends with a semicolon ;
• Class names start with a capital letter by convention, like Main or Student
• Text (a string) goes inside double quotes "like this"

Printing Output

Java has two common print methods:

• println() prints and then moves to the next line
• print() prints and stays on the same line

public class Main {
  public static void main(String[] args) {
    System.out.print("Rs ");
    System.out.print(500);
    System.out.println(" only");
    System.out.println("Thank you for shopping");
  }
}

Rs 500 only
Thank you for shopping

Printing Numbers

Numbers do not need quotes. Java can also do maths inside println:

public class Main {
  public static void main(String[] args) {
    System.out.println(45);
    System.out.println(10 + 15);
    System.out.println("10 + 15");
  }
}

45
25
10 + 15

Inside quotes, 10 + 15 is just text, so Java prints it as it is.

Comments

Comments are notes for people who read the code. Java ignores them.

• A single-line comment starts with //
• A multi-line comment starts with /* and ends with */

public class Main {
  public static void main(String[] args) {
    // This prints a greeting
    System.out.println("Hello");

    /* The next line prints the shop name.
       It is written on two lines. */
    System.out.println("Bismillah General Store"); // shop in Orangi
  }
}

Hello
Bismillah General Store

Exercise