Lesson 06 of 31

7 mins read

Primitive Data Types

In Plain English

Java data types are divided into two categories: Primitive Types (which store raw values directly in memory) and Reference Types (like String, Arrays, and Objects). Java has 8 built-in primitive types optimized for speed and memory efficiency.

The Mental Model

"Primitive types are like physical coins in your pocket: you hold the exact value. Reference types are like a bank account slip: they point to where the money is stored."

Deep Dive: How It Works

Whole numbers: `byte` (8-bit), `short` (16-bit), `int` (32-bit, default), `long` (64-bit, suffix L).

Floating points: `float` (32-bit, suffix f), `double` (64-bit, default decimal type).

Boolean: `boolean` (true or false).

Character: `char` (16-bit Unicode character, enclosed in single quotes 'A').

Syntax Blueprint

int count = 42;
double price = 19.99;
char grade = 'A';
boolean active = true;

Use single quotes for char ('Z') and double quotes for String ("Hello").

Core Rules to Remember

Default Types: int is the standard for whole numbers; double is the standard for decimals.

Char vs String: char uses single quotes ('X'); String is an object using double quotes ("X").

Long & Float Suffixes: Use 10000000000L for long and 5.75f for float.

Common Beginner Traps & How to Fix Them

Mistake:Using double quotes for char: char c = "A";

Why it happens: "A" is a String object, not a primitive char.

How to fix: Use single quotes: char c = 'A';

Pro Tip: For 95% of daily tasks, int, double, boolean, char, and String are all you need.

Live Interactive Example

Hit Run Code to see it live

The Core Java Primitives

Java 13

Output Console

Click "Run Code" to view the rendered output.

How it works: Each primitive type stores its value with precise byte size in memory.

Your Turn: Micro Challenge

No pressure! Edit the starter code below and test your solution with instant feedback.

Micro Exercise

Store product details

Declare an int variable "items" with value 5.
Declare a double variable "totalCost" with value 49.95.
Print "Items: " + items and "Total: $" + totalCost on separate lines.

Sandbox Output

Click "Run & Check" to test your solution.

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