In Java programming, what is a wrapper class and why is it used to wrap primitive data types as objects?

Introduction / Context:
In Java programming, wrapper classes are an important concept that connects primitive data types with the fully object oriented features of the language. Many Java APIs, such as collections and generics, work only with objects and cannot directly store primitive values. To solve this problem, Java provides a set of classes that wrap primitives in an object representation. Understanding what a wrapper class is and why it is used is an essential interview topic for core Java and object oriented programming.

Given Data / Assumptions:
- The question is about the definition and purpose of a wrapper class in Java.
- Java has primitive types such as int, double, boolean, and char.
- Java libraries like ArrayList and HashMap store objects, not primitive values directly.
- No numeric calculation is required, only a conceptual explanation.

Concept / Approach:
The core idea is that a wrapper class is a Java class whose main role is to hold, or wrap, a primitive value inside an object. For example, Integer wraps an int, Double wraps a double, and Boolean wraps a boolean. Once wrapped, the value can be used wherever an object is expected, such as in collections and generics. Wrapper classes also provide helpful utility methods, such as parsing from String and converting between representations. Modern Java also supports autoboxing and unboxing, which automatically converts between primitive values and their wrapper objects.

Step-by-Step Solution:
Step 1: Recall that primitives (int, double, boolean, etc.) are not objects and are stored more directly in memory.Step 2: Note that many Java APIs, especially in the java.util package, can only store and manipulate objects, not primitive values.Step 3: Recognise that wrapper classes such as Integer, Double, Character, and Boolean provide an object representation of each primitive type.Step 4: Understand that a wrapper object contains a field that stores the primitive value and exposes methods to access, convert, and process that value.Step 5: Conclude that the main purpose is to allow primitive values to participate in object oriented structures and APIs that require objects.

Verification / Alternative check:
A simple way to verify this understanding is to consider an ArrayList of int values. Java does not allow ArrayList, but it does allow ArrayList. When you add an int to an ArrayList, Java automatically wraps the int into an Integer object. This behaviour confirms that wrapper classes exist to wrap primitives in objects so they can be used in object based APIs and features such as collections and generics.

Why Other Options Are Wrong:
Option B is about hiding implementation details of a web service, which relates more to encapsulation and service abstraction, not specifically to wrapper classes. Option C describes a class that always runs in a separate thread, which matches the idea of a worker or background thread class, not a wrapper class. Option D describes a pure utility class with only static methods, such as java.lang.Math, which is different from a wrapper class that actually stores a primitive value inside an object instance.

Common Pitfalls:
A common mistake is to think that wrapper classes exist only for method overloading or only to provide utility methods. While they do offer useful methods, their key purpose is to wrap primitive values in an object. Another pitfall is to assume that using wrapper classes is always better than primitives; in fact, wrapper objects have more overhead, can be null, and may affect performance when used excessively in tight loops. Developers should choose primitives when they only need raw values and wrapper classes when integration with object based APIs or nullable values is required.

Final Answer:
Correct answer: A special class that wraps a primitive data type in an object so it can be used wherever only objects are allowed