What are the reasons for using wrapper classes?

1. Providing object-oriented representations of primitive data types. Wrapper classes (Integer, Double, Boolean, etc.) allow primitives to be treated as objects, which is necessary for working with Java collections (e.g., ArrayList, HashMap).
2. Using null values. Primitive types cannot accept null, whereas wrapper objects can. This is useful for representing the absence of a value.
3. Providing auxiliary methods. Wrapper classes contain useful static methods for type conversion, comparison, string operations, and other functions (e.g., Integer.parseInt(), Double.isNaN()).
4. Autoboxing/Unboxing. The JVM automatically converts primitives to their corresponding wrapper objects (autoboxing) and vice versa (unboxing), simplifying code when working with collections or methods expecting objects.
5. Thread safety (immutability). Most wrapper classes are immutable, making them thread-safe and convenient for use in multithreaded applications.

Example of usage in a collection:

// Creating a list to store integers
List<Integer> integerList = new ArrayList<>();

// Adding a primitive int, autoboxing occurs
integerList.add(10); 
integerList.add(20);

// Retrieving an Integer, unboxing occurs
int firstElement = integerList.get(0); 

Example of using a helper method:

String numberString = "123";
int parsedNumber = Integer.parseInt(numberString); // Converting string to int