Rewinding to the Basics

Hey everyone! 👋
This blog post is a summary of what I learned in my very first Java class. Whether you're starting Java or need a quick refresher, this post will walk you through the key concepts in a beginner-friendly way.

🧠 Evolution of Java

• Java was conceived by James Gosling and a team at Sun Microsystems in 1991.
• Initially named "OAK", it was later renamed to Java.
• Java was designed with the principle of Write Once, Run Anywhere, making it a platform-independent language.

⚙️ How Java Works

🔁 Compiler

• Converts high-level source code into bytecode.
• Unlike C/C++, Java doesn't compile to machine-specific code.
• The bytecode is portable and can run on any machine with a Java Virtual Machine (JVM).

💡 Platform Independence

1. Source Code
2. Compiled into Bytecode
3. Executed by JVM
4. Runs on any machine

🧰 Java Ecosystem

• JDK (Java Development Kit): Includes compiler + JRE + tools
• JRE (Java Runtime Environment): Includes JVM + libraries to run Java apps
• JVM (Java Virtual Machine): Executes bytecode
• JavaFX: A library to build rich user interfaces

Structure of a Java Program
Coding:x
class First {
public static void main(String[] args) {
// Code here
}
}

• First is the class name.
• public static void main(String[] args) is the main method – the entry point of every Java program.
• If a class is marked public, your file name must match the class name (e.g., First.java).

Types of Errors

Type Description
Compilation Error Happens during compilation (syntax/structure issues)
Runtime Error Occurs while running (e.g., int num = 10/0;)
Logical Error Produces incorrect results due to wrong logic

Comments in java
// Single-line comment

/*
Multi-line comment
*/

Variables & Naming Conventions
Rules:

1. Can include letters (A-Z, a-z), digits (0-9), _, $
2. Cannot begin with a digit
3. Case-sensitive
4. Cannot use Java reserved keyword 📊 Data Types in Java

🧩 Primitive Data Types
Type Size Example
byte 1 byte byte a = 127;
short 2 bytes short s = 32000;
int 4 bytes int i = 1000;
long 8 bytes long l = 100000L;
float 4 bytes float f = 10.5f;
double 8 bytes double d = 10.5;
char 2 bytes 'A'
boolean 1 bit true/false

✍️ Note:
Use L or l for long, f or F for float.

🧮 Operators
➕ Arithmetic Operators

Operator Description

• Addition
• Subtraction
• Multiplication / Division % Modulus

➕ Augmented Assignment
int num = 3;
num += 3; // same as num = num + 3;

🔄 Type Casting
Implicit (Widening)
int x = 10;
double y = x; // Automatic

Explicit (Narrowing)
double d = 9.85;
int i = (int) d; // Output: 9

⚙️ Unary Operators

1. ++a (pre-increment)
2. a++ (post-increment)
3. --a, a-- (decrement)
4. ! (logical NOT)

✅ Relational & Logical Operators
Relational

• ==, !=, <, <=, >, >=

Logical
Expression Result
true && true true
true && false false
true
false

🧪 Literal Representations

• Decimal → int a = 10;
• Binary → int b = 0b1010;
• Octal → int o = 012;
• Hexadecimal → int h = 0xA;

Bitwise Operator
Operator---Description
(<<)-------left shift
(>>)-------signed right shift
(>>>)------unsigned right shift

Wrapper Classes & Methods
Every primitive data type has a wrapper class: int → Integer, char → Character, etc.

Example:
String myName = "Abi";
System.out.print(myName); // Abi

Finally
This was a quick walkthrough of everything I learned in my first Java class — from how Java works under the hood to basic building blocks like data types and operators. These fundamentals are the stepping stones for deeper concepts ahead. I’ll continue sharing what I learn, one topic at a time, so stay tuned! 🚀

Are you also learning Java? Share your favorite learning tip or resource in the comments — let’s grow together! 💬👩‍💻