What is the difference between association and composition?

Asked By: Natividad Olloqui | Last Updated: 1st March, 2020
Category: technology and computing programming languages
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In Short, a relationship between two objects is referred as an association, and an association is known as composition when one object owns other while an association is known as aggregation when one object uses another object.

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Keeping this in consideration, what is Association aggregation and composition explain with examples?

Aggregation implies a relationship where the child can exist independently of the parent. Example: 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. Example: House (parent) and Room (child).

Beside above, what is the difference between association and inheritance? Association vs Inheritance. Another type of relationship between classes is the has-a relationship or association relationship. The 1 near the Course means that 1 course object is associated with the number shown near the other class. In this case it is * which means 0 to many.

Consequently, what is composition in object oriented programming?

Composition is one of the fundamental concepts in object-oriented programming. It describes a class that references one or more objects of other classes in instance variables. This allows you to model a has-a association between objects. You can find such relationships quite regularly in the real world.

What is the difference between composition and aggregation in C++?

Key Differences Between Aggregation and Composition As against, in composition, the child entity is dependent on the parent. In aggregation there exist a “has a” relationship whereas in composition there is a “part of” relationship between the assembly and constituent class objects.

35 Related Question Answers Found

What is association with example?

An association is a “using” relationship between two or more objects in which the objects have their own lifetime and there is no owner. As an example, imagine the relationship between a doctor and a patient. The objects that are part of the association relationship can be created and destroyed independently.

What is aggregation explain with example?

Aggregation is a way of composing different abstractions together in defining a class. For example, a car class can be defined to contain other classes such as engine class, seat class, wheels class etc. Other examples of aggregation are: A window class containing menu class, check-box class etc.

What is Association and its types?

An association type (also called an association) is the fundamental building block for describing relationships in the Entity Data Model (EDM). In a conceptual model, an association represents a relationship between two entity types (such as Customer and Order ).

What is Association class diagram?

In a UML class diagram, you can draw associations between any pair of types. A type is a class, interface, or enumeration. An association indicates that the system you are developing stores links of some kind between the instances of the associated types.

What are different types of aggregation?


Association, Aggregation, Composition, Abstraction, Generalization, Realization, Dependency
  • Association. Association is a relationship between two objects.
  • Aggregation. Aggregation is a special case of association.
  • Composition. Composition is a special case of aggregation.
  • Generalization.
  • Realization.
  • Dependency.

What do you mean by abstraction?

Abstraction (from the Latin abs, meaning away from and trahere , meaning to draw) is the process of taking away or removing characteristics from something in order to reduce it to a set of essential characteristics. Abstraction is related to both encapsulation and data hiding.

Is a relationship OOP?

One of the advantages of Object-Oriented programming language is code reuse. Object oriented programming generally support 4 types of relationships that are: inheritance , association, composition and aggregation. All these relationship is based on "is a" relationship, "has-a" relationship and "part-of" relationship.

What is meant by class diagram?

In software engineering, a class diagram in the Unified Modeling Language (UML) is a type of static structure diagram that describes the structure of a system by showing the system's classes, their attributes, operations (or methods), and the relationships among objects.

Can we achieve polymorphism through composition?

you can achieve polymorphism without inheritance using composition. Composition is an oop topic, when we create an object of a class in an other class we called it composition.

What is polymorphism in OOP?


In object-oriented programming, polymorphism refers to a programming language's ability to process objects differently depending on their data type or class. More specifically, it is the ability to redefine methods for derived classes.

What is the benefit of composition over inheritance?

2) Composition offers better test-ability of a class than Inheritance. If one class is composed of another class, you can easily create Mock Object representing composed class for sake of testing. Inheritance doesn't provide this luxury. In order to test derived class, you must need its super class.

What is a composition relationship?

Composition is a restricted form of Aggregation in which two entities are highly dependent on each other. It represents part-of relationship. In composition, both the entities are dependent on each other. When there is a composition between two entities, the composed object cannot exist without the other entity.

What is encapsulation in OOP?

Encapsulation is one of the fundamental concepts in object-oriented programming (OOP). It describes the idea of bundling data and methods that work on that data within one unit, e.g., a class in Java. This concept is also often used to hide the internal representation, or state, of an object from the outside.

When should I use composition or inheritance?

You should use inheritance when subclass "is-a" super class both structurally and functionally, when it can be used as superclass and you are going to use that. If it is not the case - it is not inheritance, but something else. Composition is when your objects consists of another, or has some relationship to them.

How do you implement a composition in C++?


To qualify as a composition, an object and a part must have the following relationship:
  1. The part (member) is part of the object (class)
  2. The part (member) can only belong to one object (class) at a time.
  3. The part (member) has its existence managed by the object (class)

Is a VS has a?

Wherever you see an extends keyword or implements keyword in a class declaration, then this class is said to have IS-A relationship. HAS-A Relationship: Composition(HAS-A) simply mean the use of instance variables that are references to other objects. For example Maruti has Engine, or House has Bathroom.

What is Association in C++ with example?

An association supports data sharing between classes or, in the case of a self-association, between objects of the same class. For example, a Customer class has a single association (1) to an Account class, indicating that each Account instance is owned by one Customer instance.