Java Syntax and First Program

# CHAPTER 3

Java Syntax and First Program #

1. Introduction #

2. Learning Objectives #

• Understand the anatomy of a Java program.

• Explain the purpose of public, static, void, and main.

• Use System.out.println() and System.out.print().

• Write single-line and multi-line comments.

• Build a basic calculator program.

3. Anatomy of a Java Program #

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

Let's break down every single keyword:

4. The main() Method — The Entry Point #

public static void main(String[] args) {
    // Your code starts here
}

Real-World Analogy: Think of main() as the front door of a building. The JVM always enters through this door first.

5. Printing Output #

System.out.println() — Prints text and moves to a new line.

System.out.println("Line 1");
System.out.println("Line 2");

Output:

Line 1
Line 2

System.out.print() — Prints text but stays on the same line.

System.out.print("Hello ");
System.out.print("World");

Output:

Hello World

System.out.printf() — Formatted output (like C's printf).

String name = "Alice";
int age = 25;
System.out.printf("Name: %s, Age: %d%n", name, age);

Output:

Name: Alice, Age: 25

6. Comments in Java #

// This is a single-line comment

/* This is a
   multi-line comment */

/**
 * This is a Javadoc comment.
 * Used to generate official API documentation.
 * @author John Doe
 */

7. Semicolons and Curly Braces #

• Every statement must end with a semicolon ;.

• Blocks of code are wrapped in curly braces { }.

public class Rules {
    public static void main(String[] args) {    // Opening brace
        System.out.println("Semicolons matter!"); // Semicolon
    }                                              // Closing brace
}

8. Escape Characters #

System.out.println("Hello\tWorld");
System.out.println("She said \"Java is amazing!\"");
System.out.println("C:\\Users\\Documents\\file.txt");

Output:

Hello	World
She said "Java is amazing!"
C:\Users\Documents\file.txt

9. Java is Case-Sensitive #

• System ≠ system

• String ≠ string

• Main ≠ main

A single wrong capitalization will crash your program.

10. Naming Conventions #

11. Mini Project: Basic Calculator #

public class BasicCalculator {
    public static void main(String[] args) {
        int a = 20;
        int b = 5;

        System.out.println("===== BASIC CALCULATOR =====");
        System.out.println("Number 1: " + a);
        System.out.println("Number 2: " + b);
        System.out.println("----------------------------");
        System.out.println("Addition:       " + (a + b));
        System.out.println("Subtraction:    " + (a - b));
        System.out.println("Multiplication: " + (a * b));
        System.out.println("Division:       " + (a / b));
        System.out.println("Modulus:        " + (a % b));
        System.out.println("============================");
    }
}

Output:

===== BASIC CALCULATOR =====
Number 1: 20
Number 2: 5
----------------------------
Addition:       25
Subtraction:    15
Multiplication: 100
Division:       4
Modulus:        0
============================

12. Common Mistakes #

• Missing semicolon: System.out.println("Hi") → Compilation error.

• Wrong class name: File is Hello.java but class is HelloWorld → Error.

• Using System.out.Println (capital P) → Java is case-sensitive, this fails.

13. Best Practices #

• Always start class names with an uppercase letter.

• Use meaningful names: calculateSalary() not cs().

• Comment your code, but don't over-comment obvious lines.

14. Exercises #

1. 1. Write a program that prints your name, age, and city on three separate lines.

1. 2. Write a program using only System.out.print() (not println) to print "Java is fun!" on one line using three separate print statements.

1. 3. Create a program that demonstrates all four escape characters.

15. MCQ Quiz with Answers #

16. Interview Questions #

• Q: Explain every keyword in public static void main(String[] args).

• Q: What is the difference between println(), print(), and printf()?

• Q: Can a Java program have multiple classes? Can it have multiple main methods?

• Q: What are Javadoc comments and how are they used?

17. FAQs #

Q: Why does Java need so much boilerplate (public class, main, etc.)? A: Java values explicitness and clarity over brevity. This verbosity helps large teams understand each other's code.

18. Summary #

19. Next Chapter Recommendation #