In Object Oriented (OO) design, it is desirable to design class that are tightly encapsulated, loosely coupled and highly cohesive, so the classes are easy to maintain and suitable for reuse.
- Encapsulation :
refers to keeping the data and method inside a class so use cannot access the data directly but via the public methods. Tight encapsulation is desired, which can be achieved by public getter and setter to the variables .
the benefit is you have complete control on how the data is to be read and how to the data is to be changed.
Another key benefit of tight encapsulation is information hiding, which means that the users are not aware (and do not need to be aware) of how the data is stored internally.
Example: ATM user knows only withdraw , deposit, and check information but they don’t know how the process inside( internal) of this functionality.
- Coupling
refer to the degree which one class relies on knowledge of the internal of the other class.
** Tight coupling is undesirable because if one class changes its internal representations, all the other tightly-coupled classes need to be rewritten.
** loose coupling is often associated with tight encapsulation. For example, well-defined public method for accessing the data, instead of directly access the data.
- Cohesion
refers to the degree to which a class or method resists being broken down into smaller pieces. High degree of cohesion is desirable. Each class shall be designed to model a single entity with its focused set of responsibilities and perform a collection of closely related tasks. also each method shall accomplish a single task. Low cohesion classes are hard to maintain and re-use.
