Class Diagram advanced concepts

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Class Diagramadvanced concepts
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Characteristics of Object Oriented Design (OOD)

• Data and operations (functions) are combined ?
  object
• Objects arte abstractions of real-world or system
  entities and manage themselves.
• Objects are independent and encapsulate state and
  represent information.
• System functionality is expressed in terms of
  object services.
• Objects communicate by message passing.

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• Objects are abstractions of real-world entities.
• Objects encapsulate state and represent
  information.
• Objects state is protected.
• Objects have responsibility.
• Objects interact by interfaces.

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Conceptions

• Encapsulation
• Information hiding
• Responsibility

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Encapsulation

• Encapsulation is the grouping of related ideas
  into one unit, which can thereafter be referred
  to by a single name.
• Object-oriented encapsulation is the packaging of
  operations and attributes representing state into
  an object type so that state is accessible or
  modifiable via the interface provided by the
  encapsulation.

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Information hiding

• Information hiding is the use of an encapsulation
  to restrict from external visibility certain
  information decisions that are internal to the
  encapsulation structure.

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Responsibility

• Object oriented design is a responsibility driven
  design approach.
• Objects have responsibilities that they prove
  oneself.
• Therefore, collaboration with other objects is
  needed.

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Objects and object classes

• Objects are entities in a software system which
  represent instances of real-world and system
  entities
• Object classes are templates for objects. They
  may be used to create objects
• Object classes may inherit attributes and
  services from other object classes

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Objects
An object is an entity which has a state and a
defined set of operations which operate on that
state. The state is represented as a set of
object attributes. The operations associated with
the object provide services to other objects
(clients) which request these services when some
computation is required. Objects are created
according to some object class definition. An
object class definition serves as a template for
objects. It includes declarations of all the
attributes and services which should be
associated with an object of that class.
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Class diagrams

• Class diagrams are the most commonly used
  diagrams in UML.
• Class diagrams are for visualizing, specifying
  and documenting the system from a static
  perspective.
• Class diagrams indicate which classes know about
  other classes and, if they do, what type of
  relationship exists.
• Class diagrams help in showing the functional
  requirements of the system by the services the
  system should provide to its end-users.

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Relationship between diagrams
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Advanced Class Features
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Advanced Class Concepts Visibility

• Visibility class members (attributes,
  operations) may be specified as
• we have feature f, an attribute or operation
  that is defined on an object O of class C
• public
• f is public ? f is visible to any object and f
  is inherited by the subclasses of C.
• private
• f is private ? f is visible only to O and f is
  not inherited by the subclasses of C.
• - protected
• (f is protected ? f is visible only to objects of
  class C and to objects of Cs subclasses and f is
  inherited by the subclasses of C.
• Restricting visibility is the same as restricting
  accessibility.

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Advanced Class Concepts Scope

• Individual member data ( attributes) may have
• Class scope a single copy of an attribute is
  shared by all instances of a class.
• Instance scope each instance of a class would
  have its own copy of the attribute.

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Advanced Class Concepts Abstract

• An operation is abstract if it has no
  implementation.
• A abstract class cannot have any direct
  instances.
• Abstract classes only occur in the context of an
  inheritance hierarchy.
• Abstract operations and classes are specified by
  writing its name in italics.

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Advanced Class Concepts Abstract
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Interfaces and Abstract Classes

• One can vary the interfaces of classes
  independent of the implementation.
• A pure interface is a class with no
  implementation and, therefore has operation
  declarations but no method bodies an fields.
• Interfaces are often declared through abstract
  classes.

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Window as Abstract Class
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Interfaces and Abstract Class

• Sub classing is not only the way to do this.
• For instance Java provides an interface
  construct, and the compiler checks that the
  implementing class provides implementations of
  all the interfaces operations.

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Lollipop notation for Interfaces
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Aggregation and Composition

• Aggregation is a special form of association that
  specifies a whole-part relationship between the
  aggregate (the whole) and a component (the part)
  aggregation is the part-of relationship. it is
  a special form of association in which a
  collection of objects, each having an independent
  existence, is associated with an single object
  unfilled diamond
• Composition is a form of aggregation with strong
  ownership and coincident lifetime of the parts by
  the whole the part object may belong to only one
  whole the parts are usually expected to live
  and die with the whole.
• (usually, any deletion of the whole is
  considered to cascade to the partsfilled
  diamond

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Aggregation and Composition Example
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Alternative notation for Composition
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Derived Associations and Attributes

• Derived associations and attributes can be
  calculated from other associations and
  attributes, respectively, on a class diagram.
• For example, an age attribute of a Person can be
  derived if you know that Persons date of birth.

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Qualified Associations

• The qualifier specifies how a specific object at
  the many end of the association is identified,
  and may be seen as a kind of key separating all
  the objects in the association.

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Relations and Constraints
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Object Diagram

• Shows a set of objects and their relationships.
• Illustrates instances of things found in class
  diagrams.
• Represents the static design view.

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Object Diagram Example