Wrapper Classes

Wrapper classes are object representations of primitive types. They let primitives be used where objects are required, like in collections, generics or with methods expecting Objects.

• Java collections like List, Map, etc. can’t store primitives
• You need wrappers to use generics
• Useful in Autoboxing + Unboxing

Primitive ↔ Wrappers

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

Example

List<Integer> nums = new ArrayList<>();
nums.add(5);          // int → Integer (autoboxing)
int n = nums.get(0);  // Integer → int (unboxing)

Common Methods

Integer.parseInt("42");      // String → int
Double.parseDouble("3.14");  // String → double
 
Integer x = Integer.valueOf(100);  // Creates Integer object

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Parent: _Casting & Types