Primitive Data Types and Wrapper Classes

 

1. Primitive Data Types in Java

Java has 8 primitive data types, which are the most basic types of data built into the language. They are not objects and are stored directly in memory for performance.

Type	Size	Default Value	Description	Example
byte	1 byte (8-bit)	0	Small integers (-128 to 127)	byte a = 10;
short	2 bytes	0	Larger than byte (-32,768 to 32,767)	short b = 1000;
int	4 bytes	0	Common for integers	int c = 12345;
long	8 bytes	0L	Very large integers	long d = 100000L;
float	4 bytes	0.0f	Single-precision decimal	float e = 3.14f;
double	8 bytes	0.0d	Double-precision decimal (default)	double f = 3.14159;
char	2 bytes	'\u0000'	Single 16-bit Unicode character	char g = 'A';
boolean	1 bit (virtual)	false	Logical true/false	boolean h = true;

📦 2. Wrapper Classes in Java

Java provides wrapper classes in the java.lang package for each primitive data type. These allow primitives to be treated as objects.

Primitive	Wrapper Class
byte	Byte
short	Short
int	Integer
long	Long
float	Float
double	Double
char	Character
boolean	Boolean

🔍 Why Use Wrapper Classes?

• Required when working with collections like ArrayList, which only store objects.

• Useful for type conversion, parsing from strings, and using object methods.

• Enable null values (primitives cannot be null).

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🔁 Autoboxing and Unboxing

Java automatically converts between primitives and wrappers:

Concept	Description	Example
Autoboxing	primitive ➝ object (wrapper class)	Integer x = 10;
Unboxing	object ➝ primitive	int y = x;

✅ Example Code

public class WrapperExample {
    public static void main(String[] args) {
        int num = 5;               // primitive
        Integer obj = num;         // autoboxing
        int num2 = obj;            // unboxing

        System.out.println("Primitive: " + num);
        System.out.println("Wrapper: " + obj);
        System.out.println("Unboxed: " + num2);
    }
}

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📝 Summary Table

Feature	Primitive Type	Wrapper Class
Memory Efficient	✅	❌
Part of Object Hierarchy	❌	✅
Works with Collections	❌	✅
Can be null	❌	✅
Autoboxed/Unboxed	—	✅