Imagine a situation where you need to store a primitive value in a data structure like an ArrayList — it can only store objects, not primitive types. Java solves this using Wrapper Classes, which wrap primitives into objects.
Understanding wrapper classes helps bridge the gap between object-oriented programming and primitive types, enabling flexibility and utility in real-world Java applications.
Wrapper Classes in Java are used to convert primitive data types into objects. Each primitive has a corresponding wrapper class in the java.lang package.
byte → Byteshort → Shortint → Integerlong → Longfloat → Floatdouble → Doublechar → Characterboolean → BooleanWrapper classes are immutable and provide utility methods for parsing and conversions. Java supports autoboxing (primitive to object) and unboxing (object to primitive).
public class WrapperExample {
public static void main(String[] args) {
int primitiveInt = 42;
// Autoboxing: primitive to object
Integer wrappedInt = primitiveInt;
// Unboxing: object to primitive
int unwrappedInt = wrappedInt;
System.out.println("Wrapped: " + wrappedInt);
System.out.println("Unwrapped: " + unwrappedInt);
}
}
import java.util.ArrayList;
public class WrapperList {
public static void main(String[] args) {
ArrayList<Integer> numbers = new ArrayList<>();
numbers.add(10); // Autoboxing
numbers.add(20);
numbers.add(30);
for (int num : numbers) {
System.out.println(num); // Unboxing
}
}
}
Storing primitive values in collections like ArrayList or HashMap requires wrapper classes.
Convert strings to primitives using wrapper methods like Integer.parseInt().
Wrapper classes are used in reflection, type conversion, and generic utility functions.
Primitive types are basic data types (like int, char) with no methods, while wrapper classes are object representations of these types that provide utility methods.
Autoboxing is the automatic conversion of a primitive type to its wrapper object. Unboxing is the reverse process. Java does this automatically when needed.
Immutability ensures thread-safety and consistent behavior, especially when used in collections and caching mechanisms.