Which concept is described by combining related data items and methods into a single class definition, including instance variables, constructors, and accessor/modifier methods?

• A. Encapsulation
• B. Aggregation
• C. Inheritance
• D. Composition

Answer: (A)

Encapsulation bundles related data and the procedures that operate on that data into a single unit, a class. By defining instance variables for state, a constructor to initialize that state, and accessor/modifier methods (getters and setters) to read or update it, the class provides a coherent interface while controlling how its internal data is accessed. This idea is distinct from aggregation (has-a relationships between objects), inheritance (building a hierarchy), and composition (one object containing others) because it centers on grouping data with the corresponding behavior and protecting the internal state through controlled access.