design basics

1. Abstraction-OOAD
An abstraction denotes the essential characteristics of
an object that distinguish it from all other kinds of
objects, relative to the perspective of the viewer.”
Example − When a class Student is designed, the
attributes enrolment_number, name, course, and
address are included while characteristics like
pulse_rate and size_of_shoe are eliminated, since they
are irrelevant in the perspective of the educational
institution

2. Encapsulation
• Encapsulation is the process of binding both
attributes and methods together within a
class.
• Through encapsulation, the internal details of a
class can be hidden from outside.
• The class has methods that provide user
interfaces by which the services provided by
the class may be used.

3. Class Hierarchy
In Grady Booch’s words,
• “Hierarchy is the ranking or ordering of
abstraction”.
• It uses the principle of “divide and conquer”.
Hierarchy allows code reusability.
The two types of hierarchies in OOA are −

4. • “IS–A” hierarchy − It defines the hierarchical
relationship in inheritance, whereby from a
super-class, a number of subclasses may be
derived which may again have subclasses and
so on.
• For example, if we derive a class Rose from a
class Flower, we can say that a rose “is–a”
flower.

5. • “PART–OF” hierarchy − It defines the
hierarchical relationship in aggregation by
which a class may be composed of other
classes.
• For example, a flower is composed of sepals,
petals, stamens, and carpel. It can be said that
a petal is a “part–of” flower.

6. Persistence
• In files or databases, the object lifespan is
longer than the duration of the process creating
the object.
• This property by which an object continues to
exist even after its creator ceases to exist is
known as persistence.

7. Dynamic binding
• Static binding is a binding in which name can
be associated with the class during
compilation time , and it is also called as early
Binding.
• Dynamic binding is a binding in which name
can be associated with the class during
execution time , and it is also called as Late
Binding

8. Inheritance
• Inheritance is the property of object-oriented
systems that allows objects to be built from
other objects.
• Inheritance is a relationship between classes
where one class is the parent class of another
derived class called base class or super class.

9. Types of inheritance
Dynamic inheritance.
• It allows objects to change and evolve over
time. Since base classes provide properties and
attributes for objects, changing base classes
changes the properties and attributes of a class.
.

10. Multiple inheritance.
• Some object-oriented systems permit a class to
inherit its state (attributes) and behaviors form
more than one super class

11. Polymorphism
• Polymorphism means that the same operation
may behave differently on different classes.
• Polymorphism allows us to write generic,
reusable code more easily, specify general
instructions and delegate the implementation
details to the objects involved.

12. Meta Classes
• If a class is an object, it must belong to a class
which is called as meta-class or a class of
classes.
• All the objects are instances of a class and all
classes are instances of a meta-class.
• Meta-classes are used by the compiler.