Java Syntax, Variables & Data Types – Core Basics Explained

Introduction

In Week 1, we learned what Java is, how it works, and how to write our first “Hello World” program.

Now it’s time to start real Java programming.

In this article, we’ll explore:

• Java program structure & syntax
• Variables in Java
• Data types (Primitive & Non-Primitive)
• Type casting
• Java naming conventions

These are fundamental concepts you must master before moving into logic and problem-solving.

Java Program Structure (Quick Recap)

A basic Java program looks like this:

public class Example {

    public static void main(String[] args) {
        // Code goes here
    }

}

Important Rules

• Every Java program has at least one class
• Execution starts from the main() method
• Java is case-sensitive
• Every statement ends with ;

What Is a Variable?

A variable is a container used to store data in memory.

Example:

int age = 25;

Here:

• int → data type
• age → variable name
• 25 → value

Java Variable Syntax

dataType variableName = value;

Example:

String name = "Mahabub";
double salary = 55000.75;
boolean isActive = true;

Java Data Types Overview

Java data types are divided into two main categories:

1️⃣ Primitive Data Types

2️⃣ Non-Primitive (Reference) Data Types

Primitive Data Types in Java

Primitive data types store simple values and are predefined by Java.

Most Commonly Used Types

In real projects, you’ll mostly use:

int
double
boolean
char

Example:

int score = 90;
double price = 199.99;
boolean isLoggedIn = false;
char grade = 'A';

Non-Primitive Data Types

Non-primitive data types store references to objects.

Examples:

• String
• Array
• Class
• Interface

String Example:

String message = "Welcome to Java";

👉 Strings are objects, not primitive types.

Difference: Primitive vs Non-Primitive

Type Casting in Java

Type casting means converting one data type into another.

1️⃣ Widening Casting (Automatic)

int num = 10;
double result = num;

✔ Safe
✔ No data loss

2️⃣ Narrowing Casting (Manual)

double value = 9.8;
int number = (int) value;

⚠ Possible data loss
⚠ Requires manual cast

Java Naming Conventions (Very Important)

Following conventions makes your code professional and readable.

Variables & Methods

int studentAge;
double totalPrice;

✔ camelCase

Class Names

class StudentProfile

✔ PascalCase

Constants

final int MAX_LIMIT = 100;

✔ UPPER_CASE

Common Beginner Mistakes

❌ Forgetting semicolon
❌ Using wrong data type
❌ Class name mismatch
❌ Not initializing variables
❌ Confusing String with string

Real-World Example Program

public class Student {

    public static void main(String[] args) {
        String name = "Rahim";
        int age = 20;
        double cgpa = 3.75;
        boolean isActive = true;

        System.out.println(name);
        System.out.println(age);
        System.out.println(cgpa);
        System.out.println(isActive);
    }

}

Summary

In this article, you learned:

• Java syntax basics
• How variables work
• Primitive & non-primitive data types
• Type casting
• Java naming conventions

These concepts are used in every Java program, from beginner to enterprise-level applications.