📝 What You’ll Learn

• What data types are
• Primitive vs reference types
• Overview of all 8 primitive types
• Type conversions (casting)

📦 What is a Data Type?

A data type defines the kind of value a variable can hold — like numbers, text, true/false, etc.

Every variable in Java must have a data type.

🔢 Primitive Data Types

Java has 8 primitive types built into the language:

Type	Description	Example
byte	8-bit integer	byte a = 100;
short	16-bit integer	short b = 2000;
int	32-bit integer	int c = 10000;
long	64-bit integer	long d = 100000L;
float	32-bit decimal	float e = 5.75f;
double	64-bit decimal (default)	double f = 19.99;
char	Single Unicode character	char g = 'A';
boolean	True or false	boolean h = true;

Use float with an f suffix, and long with an L suffix.

🧱 Reference (Non-Primitive) Data Types

These store references (addresses) to objects in memory.

Common examples:

• String
• Arrays (int[], String[])
• Classes and Objects

String name = "Java";
int[] numbers = {1, 2, 3};

🔁 Type Conversion (Casting)

🔹 Widening Conversion (automatic)

int a = 10;
double b = a;  // OK: int to double

🔸 Narrowing Conversion (manual)

double x = 9.8;
int y = (int) x;  // y = 9

💡 Default Values (for class-level variables)

Type	Default
int	0
double	0.0
boolean	false
char	\u0000
String	null

Local variables must be initialized before use.

🧠 Tip:

Prefer int for whole numbers, double for decimals unless you need precision control (use float).

📘 Recap

• Java has 8 built-in primitive types and many reference types
• Use the right type for the right job
• Type conversions let you shift between compatible types
• Reference types point to objects, not raw data