Data Abstraction and Encapsulation

Data Types (HSM Ch.1.3)
- A data type is a collection of objects and a set of operations that act on those objects.
- Natural data types
  - Books
  - Students
  - Beers
- Simple computer data types (often predefined in a programming language)
  - int
  - float
  - char
- Aggregate computer data types (often user defined)
  - Arrays, e.g.,
```
const int MAX_STRING_LENGTH = 80;
typedef char string[MAX_STRING_LENGTH + 1];
```
  - structs, e.g.,
```
typedef struct {
    string StudentName;
    int NumberOfBooks;
    char Grade;
    } student_record;
```
  - Data members of classes, e.g., smartintarrayclass.h
Abstract Data Types (HSM Ch.1.3)
- Data abstraction separates the specification of a data type from its implementation.
- An abstract data type is a specification of a collection of objects and a set of operations that act on those objects.
Some ADTs
- The Natural Number ADT (HSM Ch.1.3)
- Natural data types
- Simple computer data types
- Aggregate computer data types
Benefits of Using ADTs (HSM Ch.1.3)
- Modularity: each data type can be considered independently.
- Testing: data type implementations can be tested separately to check that they meet the specifications.
- Division of labour: separate implementation of data types according to agreed specifications.
- Reusability: implemented data types can be reused.
- Change of implementation: the implementation can be changed with no effect to users.
Data Encapsulation (HSM Ch.1.3)
- Data encapsulation conceals the implementation of a data type from the user.
- Benefits
  - Change of implementation: the implementation can be changed with no effect to users.
  - Prevents corruption: users are not able to manipulate the data directly, hence incorrectly.
- Data encapsulation is a natural technique when implementing ADTs, due to the separation of the specification from the implementation.

Exercises

ADTs: HSM Ch.1.3, exercises 1-4.

Lab Tasks

Exam Style Questions

Define {data type,data abstraction,data encapsulation,abstract data type}.
Give an example of an abstract data type.
List five benefits of using ADTs, giving a short explanation of each.
List two benefits of using data encapsulation, giving a short explanation of each.