Java Programming's Game-Changer: Spring AI

Core Java ♨️

Before building big programs, let’s learn the building blocks of Java. Think of this like learning the ABC of a language before writing full sentences.

Variables – “The Containers”

A variable is like a box where you store information (numbers, words, etc.) to use later.

·         You give the box a name.

·         You put some data inside it.

Example in Real Life:
Think of a water bottle.

·         The bottle’s name is the variable name.

·         The water inside is the data stored.

·         If you pour out and refill, you change the value of the variable.

Rules for Declaring a Variable Name in Java

When you create a variable in Java, you must follow some rules so the computer understands it.
Think of it like naming your pet 🐶—you can choose any name, but there are a few restrictions!

Rules:

1. Must start with a letter, $ or _

• You can’t start with a number.
• ✔️ Correct: age, _count, $salary
• ❌ Wrong: 1number, @price

Real-Life Example:
Just like your name can’t start with a number (no one is called “3John”), variable names can’t either.

 

2. Can only contain letters, numbers, $ or _

• ✔Correct: student1, total_amount, $rate
• ❌ Wrong: total-amount, price@

Real-Life Example:
Think of writing your name on a school form 📝—you can use letters, maybe numbers (like Roll No. 5), but not special symbols like @ or #.

3.    No spaces allowed

o    ✔️ Correct: firstName, totalMarks

o    ❌ Wrong: first name, total marks

Real-Life Example:
You can’t keep your Wi-Fi password with spaces in between randomly—it must be continuous. Same with variable names.

4. Case-sensitive (upper vs. lower case matters)

• Age and age are treated as two different variables.

Real-Life Example:
Just like “RAM” (the god) and “ram” (a boy’s name) mean different things, Java also treats uppercase and lowercase differently.

 

5. Should not be a keyword

• You can’t use reserved words like class, if, for.
• ✔Correct: studentAge
• ❌ Wrong: class

Real-Life Example:
Imagine trying to name your shop “Police Station” 🚓—not allowed, because that name is already reserved for government use.

6. Use meaningful names (good practice)

• ✔Good: customerName, totalPrice
• ❌ Bad: x, y, abc

Real-Life Example:
Naming your child “Kid1” and “Kid2” may confuse you later 😅. Better to use meaningful names like “Aman” or “Riya.”

👉 In short:

• Start with letter, _, or $.
• Use only letters, numbers, _, $.
• No spaces.
• Case-sensitive.
• Don’t use reserved words.
• Always choose clear, meaningful names.

Key Elements of Java Basic Syntax:

• Case Sensitivity: 

  Java is case-sensitive.
• MyVariable and myvariable are treated as different identifiers.
• Class Names: 

  Class names typically start with an uppercase letter and follow PascalCase (e.g., MyClass, HelloWorld).
• 
  
Method Names: 
Method names usually start with a lowercase letter and follow camelCase (e.g., myMethod, calculateSum).


File Naming: 
If a Java file contains a public class, the file name must exactly match the public class name, including case, and end with the .java extension (e.g., HelloWorld.java for a public class HelloWorld).



public static void main(String[] args):  
This is the entry point for every Java application.
public:  Makes the method accessible from anywhere.
static: Allows the method to be called without creating an instance of the class.
void: Indicates that the method does not return any value.
main: The name of the method.
(String[] args): Declares a parameter that accepts an array of strings, typically used for command-line arguments.
Curly Braces {}: 
Used to define code blocks for classes, methods, loops, and conditional statements.
Semicolons ;: 
Terminate statements in Java. Every executable statement must end with a semicolon.
Comments: 
Used to add explanations to the code, ignored by the compiler.
Single-line comments: // This is a single-line comment
Multi-line comments: /* This is a multi-line comment */
Documentation comments: /** This is a documentation comment */
Variables: 
Declared before use, specifying their data type and name (e.g., int age = 30;).
Keywords: 
Reserved words with special meaning in Java that cannot be used as identifiers (e.g., public, class, int, if, else).


Writer - Inderjit Singh ✍🏼