Java-learnings

📌 Data Types in Java

In Java, data types are broadly classified into two categories:

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1️⃣ Primitive Data Types

Primitive data types are basic, built-in data types provided by Java. They store simple values directly.

Types of Primitive Data Types:

• byte
• short
• int
• long
• float
• double
• boolean
• char

Key Characteristics:

• Predefined in Java
• Store actual values
• Start with lowercase letters
• Cannot call methods
• Cannot be null

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2️⃣ Non-Primitive Data Types (Reference Types)

Non-primitive data types are used to store references to objects rather than the actual data.

Examples of Non-Primitive Data Types:

• String
• Arrays
• Classes
• Interfaces

Key Characteristics:

• Mostly created by the programmer (Exception: String is provided by Java)
• Store references to objects
• Can call methods to perform operations
• Usually start with uppercase letters
• Can have a value of null

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🔍 Difference Between Primitive and Non-Primitive Data Types

Feature	Primitive Data Types	Non-Primitive Data Types
Definition	Built-in data types	User-defined (except String)
Data Storage	Stores actual value	Stores reference to an object
Method Support	Cannot call methods	Can call methods
Case Style	Lowercase (int)	Uppercase (String)
Null Value	Cannot be null	Can be null
Examples	int, char, boolean	String, Arrays, Classes

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📌 The var Keyword in Java

The var keyword was introduced in Java 10 (released in 2018).

It allows the compiler to automatically infer the data type of a variable based on the value assigned to it. This helps reduce verbosity and makes code cleaner and more readable, especially when dealing with long or complex types.

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🔹 Basic Example

Instead of explicitly declaring a type:

int x = 5;

You can write:

var x = 5;   // x is inferred as int
System.out.println(x);

The compiler determines that 5 is an int, so x becomes an int.

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🔹 Examples with Different Data Types

The inferred type depends on the value assigned:

var myNum = 5;           // int
var myDouble = 9.98;     // double
var myChar = 'D';        // char
var myBoolean = true;    // boolean
var myString = "Hello";  // String

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⚠️ Important Notes About var

1️⃣ Initialization Is Mandatory

You must assign a value at the time of declaration.

var x;       // ❌ Error
var x = 5;   // ✅ Valid

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2️⃣ Type Is Fixed After Inference

Once the compiler infers the type, it cannot be changed.

var x = 5;   // x is inferred as int
x = 10;      // ✅ OK (still an int)
x = 9.99;    // ❌ Error (double cannot be assigned to int)

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3️⃣ var Is Not Dynamically Typed

Although var looks flexible, Java remains statically typed. The type is decided at compile time, not at runtime.

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✅ Summary

• var improves readability by reducing redundant type declarations
• The type is inferred only once and remains fixed
• Initialization is required
• Java does not become dynamically typed with var

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