Introduction to Java

Java is a high-level, object-oriented programming language that’s designed to be portable — “Write Once, Run Anywhere (WORA).” In this blog post, we’ll cover the basics of Java programming, including setting up your environment, writing your first program, and understanding variables and data types.

That means code written on one system can run on any other system that has a Java Virtual Machine (JVM).

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☕ The Java Ecosystem

Component	Full Form	Purpose
JVM	Java Virtual Machine	Runs Java bytecode (compiled Java programs). Makes Java platform-independent.
JRE	Java Runtime Environment	Provides libraries + JVM needed to run Java applications. (Runtime only, not for development.)
JDK	Java Development Kit	Includes everything in JRE + development tools (like compiler javac) to write and compile Java code.

In short:

JDK = JRE + Development Tools
JRE = JVM + Libraries

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2. Writing Your First Java Program

Step 1: Install Java

Download & install the latest JDK from Oracle or OpenJDK.

Step 2: Write a Program

Create a file named HelloWorld.java

// This is a simple Java program
public class HelloWorld {
    public static void main(String[] args) {
        System.out.println("Hello, World!");
    }
}

Step 3: Compile and Run

Open your terminal in the file’s directory and type:

javac HelloWorld.java     // Compiles the code → creates HelloWorld.class
java HelloWorld           // Runs the program

Output:

Hello, World!

3. Variables and Data Types

Variables

A variable stores data.

Syntax:

type variableName = value;

Example:

int age = 25;
String name = "Alice";
double price = 19.99;

Data Types in Java

Type	Example	Description
int	int x = 10;	Integer numbers
double	double pi = 3.14;	Decimal numbers
char	char grade = 'A';	Single character
boolean	boolean isJavaFun = true;	True or False
String	String name = "Bob";	Sequence of characters (not primitive)

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Example Program with Variables

public class VariablesExample {
    public static void main(String[] args) {
        int age = 20;
        double height = 5.9;
        char grade = 'A';
        boolean isStudent = true;
        String name = "Emma";

        System.out.println("Name: " + name);
        System.out.println("Age: " + age);
        System.out.println("Height: " + height);
        System.out.println("Grade: " + grade);
        System.out.println("Is Student: " + isStudent);
    }
}

Output:

Name: john
Age: 20
Height: 5.9
Grade: A
Is Student: true

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Summary

• JVM runs the code, JRE lets you run it, JDK lets you write it.
• Java programs start from the main() method.
• Variables store data using various data types.
• System.out.println() prints output to the console.

Happy hacking!