OO Class Relationships | Atomic Object
Quick answer to a UML FAQ: Association vs Aggregation vs Composition? and similarities between the classes of the following objects: pets, cats, tails, owners. Actually, Aggregation and Composition are subsets of association meaning they Aggregation implies a relationship where the child can exist independently. When a class definition uses another class as a parameter to a method, or declares an Associations are the most generic of the relationships between classes. We're going to look at the way we define the relationships between classes so we know aggregation; inheritance; using; association; instantiation Class relationships are of course visible in source code, but can also be defined graphically.
Actually, Aggregation and Composition are subsets of association meaning they are specific cases of association.
Lecture Notes on Object-Oriented Programming
In both aggregation and composition object of one class "owns" object of another class. But there is a subtle difference: Aggregation implies a relationship where the child can exist independently of the parent. Class parent and Student child. Delete the Class and the Students still exist.
Composition implies a relationship where the child cannot exist independent of the parent.association in c++ - OOPS
House parent and Room child. Rooms don't exist separate to a House. We should be more specific and use the composition link in cases where in addition to the part-of relationship between Class A and Class B - there's a strong lifecycle dependency between the two, meaning that when Class A is deleted then Class B is also deleted as a result Aggregation Example: It's important to note that the aggregation link doesn't state in any way that Class A owns Class B nor that there's a parent-child relationship when parent deleted all its child's are being deleted as a result between the two.
Actually, quite the opposite! Summing it up - To sum it up association is a very generic term used to represent when on class used the functionalities provided by another class.
We say it's a composition if one parent class object owns another child class object and that child class object cannot meaningfully exist without the parent class object. If it can then it is called Aggregation. Generalization vs Specialization Generalization is a mechanism for combining similar classes of objects into a single, more general class.
Generalization identifies commonalities among a set of entities. The commonality may be of attributes, behavior, or both. In other words, a superclass has the most general attributes, operations, and relationships that may be shared with subclasses.
UML Association vs Aggregation vs Composition
Operations are also referred as functions or methods. Example Let us consider a simple class, Circle, that represents the geometrical figure circle in a two—dimensional space. Encapsulation and Data Hiding 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. It permits the elements of the class to be accessed from outside only through the interface provided by the class.
Data Hiding Typically, a class is designed such that its data attributes can be accessed only by its class methods and insulated from direct outside access. It should instead be accessed through the methods setValues and getValues. Message Passing Any application requires a number of objects interacting in a harmonious manner. Objects in a system may communicate with each other using message passing.
Suppose a system has two objects: The object obj1 sends a message to object obj2, if obj1 wants obj2 to execute one of its methods. Message passing enables all interactions between objects. Message passing essentially involves invoking class methods. Objects in different processes can be involved in message passing.
OOAD - Object Model
Inheritance Inheritance is the mechanism that permits new classes to be created out of existing classes by extending and refining its capabilities. The subclass can inherit or derive the attributes and methods of the super-class es provided that the super-class allows so.
Besides, the subclass may add its own attributes and methods and may modify any of the super-class methods. Humans, cats, dogs, and cows all have the distinct characteristics of mammals. In addition, each has its own particular characteristics. The following figure depicts the examples of different types of inheritance. Polymorphism Polymorphism is originally a Greek word that means the ability to take multiple forms. In object-oriented paradigm, polymorphism implies using operations in different ways, depending upon the instance they are operating upon.
Polymorphism allows objects with different internal structures to have a common external interface. Polymorphism is particularly effective while implementing inheritance. Example Let us consider two classes, Circle and Square, each with a method findArea. Though the name and purpose of the methods in the classes are same, the internal implementation, i.
When an object of class Circle invokes its findArea method, the operation finds the area of the circle without any conflict with the findArea method of the Square class. Generalization and Specialization Generalization and specialization represent a hierarchy of relationships between classes, where subclasses inherit from super-classes.
Generalization In the generalization process, the common characteristics of classes are combined to form a class in a higher level of hierarchy, i.
Specialization Specialization is the reverse process of generalization. Here, the distinguishing features of groups of objects are used to form specialized classes from existing classes.
It can be said that the subclasses are the specialized versions of the super-class. The following figure shows an example of generalization and specialization. Links and Association Link A link represents a connection through which an object collaborates with other objects.