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Class Diagram advanced concepts. 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.
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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.
Objects are abstractions of real-world entities. Objects encapsulate state and represent information. Object’s state is protected. Objects have responsibility. Objects interact by interfaces.
Conceptions • Encapsulation • Information hiding • Responsibility
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.
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.
Responsibility • Object oriented design is a responsibility driven design approach. • Objects have responsibilities that they prove oneself. • Therefore, collaboration with other objects is needed.
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
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.
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.
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 C’s subclasses and f is inherited by the subclasses of C.} • Restricting visibility is the same as restricting accessibility.
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.
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.
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.
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 interface’s operations.
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 parts}{filled diamond}
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 Person’s date of birth.
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.
Object Diagram • Shows a set of objects and their relationships. • Illustrates instances of things found in class diagrams. • Represents the static design view.
