Association vs aggregation and vs composition



Association:-  Association is relationship where both container object and contained class has it own life cycle and no one is owner is here.

Example :-
Consider student is taught by multiple teachers where Student is container object containing list of teachers. So Teacher is contained object .

What life cycle means here
 Even student is deleted, teacher will continue to exist.

What owner means here
Same teacher can be associated more more student. So student is not owner of that teacher.

What association means to developer
It tells clearly to developer when student is deleted , teacher can stay in memory(or DB) if required . May be it can be associated with further students

Aggregation:-  Aggregation is relationship where both container object and contained object has it own life cycle and but container object is the owner of contained object . It is represented by has a relationship.

Example :-
Consider department has multiple teachers.

What life cycle means here
 Even departments is deleted, teacher will continue to exist

What owner means here
Same teacher can be associated any other department or any other university at one point of time. So department is the owner of that teacher. Yes, if relationship b/w department and that teacher ends then same teacher can't be associated with other department

What association means to developer
It tells clearly to developer when department is deleted , teacher can stay in memory(or DB) if required . so far same as aggregation. Here comes the difference from aggregation. It also tells the developer that at one point of time contained object can have relationship with only one container object


Composition:-  Composition is relationship where life cycle  of contained object is dependent on life cycle of container object . It is stronger form of aggregation  When I say stronger form of aggregation , I mean container object is strong owner of contained object where contained object is bind with life cycle of container object. Also contained object can not linked with any other object. It is also represented by has a relationship.

Example :-
Consider House has number .of rooms

What life cycle means here
 House is deleted, rooms also needs to be deleted.

What strong owner means here
 Contained object is completely binded with life cycle of container object. Also contained object can not linked with any other object

What association means to developer
It tells clearly to developer when house is deleted , room also needs to be deleted from  memory(or DB) if required . 

Comments

Post a Comment

Popular posts from this blog

How to solve javax.net.ssl.SSLHandshakeException ?

This blog is about how two secured web application on SSL can communicate with each other without get certificate error i.e. SSLHandshakeException Error developer generally face When web_application_A with self signed certificate  tries to connect to web_application_B (with same self signed certificate), sometimes you must have got below error detailed message sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target cause javax.net.ssl.SSLHandshakeException: sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target Details oF mine environment :-  I got same error . Here are the environment details Webserver :- Tomcat -6 OS :- Windows 7 Java Version :- 1.6 web_application_A :- Port 8443 web_applicat...
Read more

When to use Java 8 Optional instead of traditional null pointer check ?

My project has recently moved to Java 8. Now, I see applications flooded with Optional objects mainly to check the Null Pointer on an object. Before Java 8  code style to check the null pointer Employee employee = employeeServive.getEmployee(); if(employee!=null){     System.out.println(employee.getId()); } After java 8  code style to check the null pointer Optional<Employee> employeeOptional = Optional.ofNullable(employeeService. getEmployee()); // Another way of implementing above  where service itself will return Optional<Employee> employeeOptional = employeeService.getEmployee(); if(employeeOptional.isPresent()){     Employee employee = employeeOptional.get();     System.out.println(employee.getId()); } Which one is better to check Null Pointer I see  style 1 is better when intention is just to check Null Pointer. So I find, style 1 is more clear and lesser lines of code. In this case I see devs are...
Read more

What is REST actually?

 REST is about creating representation(like JSON or XML or any other format.) of object's current state(like data in database) and transferring that representation over network. Rest is the set of constraint/convention. Resources are decoupled from their representation so that their content can be accessed in a variety of formats, such as HTML, XML, plain text, PDF, JPEG, JSON, and others. Metadata about the resource is available and used, for example, to control caching, detect transmission errors, negotiate the appropriate representation format, and perform authentication or access control At ground level , Rest is nothing more but a collection of principles  Communication should be stateless : Server should not store any state . If required it should be part of message  State should be representational : Internally resource at server can be in one form but it should be able to change it representation. An object referenced by one URI can have different forma...
Read more