Encapsulation & Information hiding
When the size of a program reaches beyond a few thousand lines, two practical
problems appear. From the programmer’s point of view, having such a program appear as
a single collection of subprograms does not impose an adequate level of organization on
the program to keep it intellectually manageable.
One solution is to organize the program into syntactic containers that include groups of
logically related subprograms and data. These syntactic containers are often called
modules, and the process of designing them is called modularization.
The second practical problem for larger programs is recompilation. In case of a small
program, recompiling the whole program after each modification is not costly. But when
programs grow beyond a few thousand lines, the cost of recompilation ceases to be
insignificant. So there is an obvious need to find ways to avoid recompilation of the parts
of a program that are not affected by a change. This can be provided by organizing
programs into collection of subprograms and data, each of which can be compiled
without recompilation of the rest of the program. Such a collection is called a
compilation unit.
An encapsulation is a grouping of subprograms and the data they manipulate. An
encapsulation, which is either separately or independently compilable, provides an
abstracted system and a logical organization for a collection of related computations.
Therefore, an encapsulation solves both of the practical problems described above.
Encapsulation are often placed in libraries and made available for reusing programs other
than those for which they were written.
Information Hiding
Information hiding is manifested by enabling programmers to restrict access to
certain data and code. This way, a class may prevent other classes and functions from
accessing its data members and some of its member functions, while allowing them to
access its non-restricted members
