Data Types

8 min read

Understanding Data Types

Data types specify the type of data a variable can hold. Java is a strongly typed language, meaning every variable must be declared with a type before use.

Primitive Data Types

Primitive types are the basic building blocks. They are not objects and store single values in memory.

Type	Size	Range	Example
byte	1 byte	-128 to 127	byte age = 25;
short	2 bytes	-32,768 to 32,767	short year = 2025;
int	4 bytes	-2³¹ to 2³¹-1	int count = 1000;
long	8 bytes	-2⁶³ to 2⁶³-1	long id = 123456789L;
float	4 bytes	±3.4×10³⁸	float price = 19.99f;
double	8 bytes	±1.7×10³⁰⁸	double pi = 3.14159;
char	2 bytes	0 to 65,535 (Unicode)	char initial = 'J';
boolean	1 bit	true or false	boolean isActive = true;

Reference Data Types

Reference types don't store the actual data but store a reference (address) to the data in memory. They include classes, interfaces, arrays, and strings.

🔑 Key Difference: Primitive types are passed by value, while reference types are passed by reference.

Code Examples

Declaration and initialization of all primitive data types

java

1// Primitive data types
2byte age = 25;
3short temperature = -10;
4int population = 7800000000;
5long distance = 384400000L;
6float price = 29.99f;
7double pi = 3.14159265;
8char grade = 'A';
9boolean isJavaFun = true;

Examples of reference data types - strings, arrays, collections, and objects

java

1// Reference data types
2String name = "John Doe";           // String object
3int[] scores = {95, 87, 92};         // Array of integers
4ArrayList<String> cities = new ArrayList<>();  // Collection
5Student student = new Student();     // Custom class object

Understanding the difference between primitive and reference type assignments

java

1// Demonstrating primitive vs reference
2public class DataTypeDemo {
3    public static void main(String[] args) {
4        // Primitive - copy by value
5        int a = 10;
6        int b = a;  // b gets the value 10
7        b = 20;     // changing b doesn't affect a
8        System.out.println(a); // Output: 10
9        
10        // Reference - copy by reference
11        int[] arr1 = {1, 2, 3};
12        int[] arr2 = arr1;     // arr2 points to same array
13        arr2[0] = 99;          // changing arr2 affects arr1
14        System.out.println(arr1[0]); // Output: 99
15    }
16}

Use Cases

Choosing appropriate data types for variables to save memory
Avoiding integer overflow by using long instead of int
Working with floating-point calculations (double for precision)
Processing character data and Unicode
Creating boolean conditions for control flow

Common Mistakes to Avoid

Using int for very large numbers instead of long
Assuming float has same precision as double
Forgetting the L suffix for long literals
Forgetting the f suffix for float literals
Confusing == operator with .equals() method for reference types
Not understanding that variables store values, not the objects themselves for primitives

Understanding Data Types

Primitive Data Types

Reference Data Types

Code Examples

Use Cases

Common Mistakes to Avoid

AI Tutor

Sign in Required