Data Types in Java | Core Java

📖 Overview

What are Data Types in Java?

Data types in Java specify the size and type of values a variable can hold. They help the compiler allocate appropriate memory and enforce type safety during operations. Java data types are divided into two main categories: Primitive Data Types and Non-Primitive Data Types.

🔢 Primitive Data Types

Primitive Data Types in Java

Primitive data types are the most basic data types available in Java. They are predefined by the language and named by a reserved keyword.

Data Type	Size	Range / Values	Default Value
byte	1 byte	-128 to 127	0
short	2 bytes	-32,768 to 32,767	0
int	4 bytes	-2,147,483,648 to 2,147,483,647	0
long	8 bytes	-9,223,372,036,854,775,808 to 9,223,372,036,854,775,807	0L
float	4 bytes	approximately ±3.40282347E+38F (6-7 significant digits)	0.0f
double	8 bytes	approximately ±1.79769313486231570E+308 (15 significant digits)	0.0d
char	2 bytes	0 to 65,535 (Unicode characters)	'u0000'
boolean	1 bit	true or false	false

📂 Categories

Categories of Data Types

Java divides data types into two main categories:

Primitive Data Types

byte → 1 byte, stores -128 to 127 (whole numbers)
short → 2 bytes, stores -32,768 to 32,767
int → 4 bytes, stores whole numbers (most commonly used)
long → 8 bytes, stores large whole numbers (suffix L/l required)
float → 4 bytes, stores fractional numbers (suffix F/f required)
double → 8 bytes, stores double-precision fractional numbers
char → 2 bytes, stores a single character/letter or ASCII values
boolean → 1 bit, stores true or false values

Non-Primitive Data Types

String → Stores sequence of characters (text)
Arrays → Collection of similar data types
Classes → User-defined data types (objects)
Interfaces → Contract for classes to implement
Collections → ArrayList, HashSet, HashMap etc.

💻 Code Example

Data Types Example Program

        public class DataTypesExample {
    public static void main(String[] args) {
        // Primitive Data Types
        byte myByte = 100;
        short myShort = 10000;
        int myInt = 100000;
        long myLong = 10000000000L;  // L suffix required
        
        float myFloat = 3.14f;       // f suffix required
        double myDouble = 3.14159265359;
        char myChar = 'A';
        boolean isJavaFun = true;
        
        // Non-Primitive Data Types
        String myText = "Hello, Java!";
        int[] myArray = {1, 2, 3, 4, 5};
        
        System.out.println("byte: " + myByte);
        System.out.println("short: " + myShort);
        System.out.println("int: " + myInt);
        System.out.println("long: " + myLong);
        System.out.println("float: " + myFloat);
        System.out.println("double: " + myDouble);
        System.out.println("char: " + myChar);
        System.out.println("boolean: " + isJavaFun);
        System.out.println("String: " + myText);
        System.out.print("Array: ");
        for (int num : myArray) {
            System.out.print(num + " ");
        }
    }
}
      

📤 Output:

byte: 100
short: 10000
int: 100000
long: 10000000000
float: 3.14
double: 3.14159265359
char: A
boolean: true
String: Hello, Java!
Array: 1 2 3 4 5

⚖️ Comparison

Primitive vs Non-Primitive Data Types

🔢 Primitive Data Types

Predefined by Java language
Stored in stack memory
Cannot be null
Have default values
Fast performance

📦 Non-Primitive Data Types

Created by programmers (except String)
Stored in heap memory
Can be null
No default values (null reference)
Slightly slower due to object overhead

🏆 Best Practices

Best Practices for Using Data Types

Use int for small numbers and long for large numbers

Use double for decimals unless precision is critical

Use float only when memory constraints matter

Always add suffix L for long and F for float values

Use String instead of char arrays for text manipulation

Avoid unnecessary type conversions to reduce performance overhead