Association, Aggregation, Composition, Abstraction, Generalization, Realization, Dependency

Association, Aggregation, Composition, Abstraction, Generalization, Realization, Dependency:

These terms signify the relationships between classes. These are the building blocks of object oriented programming and very basic stuff. But still for some, these terms look like Latin and Greek. Just wanted to refresh these terms and explain in simpler terms.

Association

Association is a relationship between two objects. In other words, association defines the multiplicity between objects. You may be aware of one-to-one, one-to-many, many-to-one, many-to-many all these words define an association between objects. Aggregation is a special form of association. Composition is a special form of aggregation.

Example: A Student and a Faculty are having an association.

Aggregation

Aggregation is a special case of association. A directional association between objects. When an object ‘has-a’ another object, then you have got an aggregation between them. Direction between them specified which object contains the other object. Aggregation is also called a “Has-a” relationship.

Composition

Composition is a special case of aggregation. In a more specific manner, a restricted aggregation is called composition. When an object contains the other object, if the contained object cannot exist without the existence of container object, then it is called composition.

Example: A class contains students. A student cannot exist without a class. There exists composition between class and students.

Difference between aggregation and composition

Composition is more restrictive. When there is a composition between two objects, the composed object cannot exist without the other object. This restriction is not there in aggregation. Though one object can contain the other object, there is no condition that the composed object must exist. The existence of the composed object is entirely optional. In both aggregation and composition, direction is must. The direction specifies, which object contains the other object.

Example: A Library contains students and books. Relationship between library and student is aggregation. Relationship between library and book is composition. A student can exist without a library and therefore it is aggregation. A book cannot exist without a library and therefore its a composition. For easy understanding I am picking this example. Don’t go deeper into example and justify relationships!

Abstraction

Abstraction is specifying the framework and hiding the implementation level information. Concreteness will be built on top of the abstraction. It gives you a blueprint to follow to while implementing the details. Abstraction reduces the complexity by hiding low level details.

Example: A wire frame model of a car.

Generalization

Generalization uses a “is-a” relationship from a specialization to the generalization class. Common structure and behaviour are used from the specializtion to the generalized class. At a very broader level you can understand this as inheritance. Why I take the term inheritance is, you can relate this term very well. Generalization is also called a “Is-a” relationship.

Example: Consider there exists a class named Person. A student is a person. A faculty is a person. Therefore here the relationship between student and person, similarly faculty and person is generalization.

Realization

Realization is a relationship between the blueprint class and the object containing its respective implementation level details. This object is said to realize the blueprint class. In other words, you can understand this as the relationship between the interface and the implementing class.

Example: A particular model of a car ‘GTB Fiorano’ that implements the blueprint of a car realizes the abstraction.

Dependency

Change in structure or behaviour of a class affects the other related class, then there is a dependency between those two classes. It need not be the same vice-versa. When one class contains the other class it this happens.

Example: Relationship between shape and circle is dependency.

Refer how these are used in representing relationships among classes in a UML class diagram at
http://en.wikipedia.org/wiki/Class_diagram



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New Interview Questions for Senior Software Engineers - Scott Hanselman

New Interview Questions for Senior Software Engineers - Scott Hanselman:

Here's what I have so far.

• What is something substantive that you've done to improve as a developer in your career?
• Would you call yourself a craftsman (craftsperson) and what does that word mean to you?
• Implement a <basic data structure> using <some language> on <paper|whiteboard|notepad>.
• What is SOLID?
• Why is the Single Responsibility Principle important?
• What is Inversion of Control? How does that relate to dependency injection?
• How does a 3 tier application differ from a 2 tier one?
• Why are interfaces important?
• What is the Repository pattern? The Factory Pattern? Why are patterns important?
• What are some examples of anti-patterns?
• Who are the Gang of Four? Why should you care?
• How do the MVP, MVC, and MVVM patterns relate? When are they appropriate?
• Explain the concept of Separation of Concerns and it's pros and cons.
• Name three primary attributes of object-oriented design. Describe what they mean and why they're important.
• Describe a pattern that is NOT the Factory Pattern? How is it used and when?
• You have just been put in charge of a legacy code project with maintainability problems. What kind of things would you look to improve to get the project on a stable footing?
• Show me a portfolio of all the applications you worked on, and tell me how you contributed to design them.
• What are some alternate ways to store data other than a relational database? Why would you do that, and what are the trade-offs?
• Explain the concept of convention over configuration, and talk about an example of convention over configuration you have seen in the wild.
• Explain the differences between stateless and stateful systems, and impacts of state on parallelism.
• Discuss the differences between Mocks and Stubs/Fakes and where you might use them (answers aren't that important here, just the discussion that would ensue).
• Discuss the concept of YAGNI and explain something you did recently that adhered to this practice.
• Explain what is meant by a sandbox, why you would use one, and identify examples of sandboxes in the wild.
• Concurrency
  • What's the difference between Locking and Lockless (Optimistic and Pessimistic) concurrency models?
  • What kinds of problems can you hit with locking model? And a lockless model?
  • What trade offs do you have for resource contention?
  • How might a task-based model differ from a threaded model?
  • What's the difference between asynchrony and concurrency?
• Are you still writing code? Do you love it?
• You've just been assigned to a project in a new technology how would you get started?
• How does the addition of Service Orientation change systems? When is it appropriate to use?
• What do you do to stay abreast of the latest technologies and tools?
• What is the difference between "set" logic, and "procedural" logic. When would you use each one and why?
• What Source Control systems have you worked with?
• What is Continuous Integration?  Have you used it and why is it important?
• Describe a software development life cycle that you've managed.
• How do you react to people criticizing your code/documents?
• Whose blogs or podcasts do you follow? Do you blog or podcast?
• Tell me about some of your hobby projects that you've written in your off time.
• What is the last programming book you read?
• Describe, in as much detail as you think is relevant, as deeply as you can, what happens when I type "cnn.com" into a browser and press "Go".
• Describe the structure and contents of a design document, or a set of design documents, for a multi-tiered web application.
• What's so great about <cool web technology of the day>?
• How can you stop your DBA from making off with a list of your users’ passwords?
• What do you do when you get stuck with a problem you can't solve?
• If your database was under a lot of strain, what are the first few things you might consider to speed it up?
• What is SQL injection?
• What's the difference between unit test and integration test?
• Tell me about 3 times you failed.
• What is Refactoring ? Have you used it and it is important? Name three common refactorings.
• You have two computers, and you want to get data from one to the other. How could you do it?
• Left to your own devices, what would you create?
• Given Time, Cost, Client satisfaction and Best Practices, how will you prioritize them for a project you are working on? Explain why.
• What's the difference between a web server, web farm and web garden? How would your web application need to change for each?
• What value do daily builds, automated testing, and peer reviews add to a project? What disadvantages are there?
• What elements of OO design are most prone to abuse? How would you mitigate that?
• When do you know your code is ready for production?
• What's YAGNI? Is this list of questions an example?
• Describe to me some bad code you've read or inherited lately.

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Java Design Patterns 101 - IBM developerworks

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Tradeworx, Inc. Public Commentary on SEC Market Structure Concept Release

Tradeworx, Inc. Public Commentary
on
SEC Market Structure Concept Release


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Nice Interview article complemented with my comments

The Guerrilla Guide to Interviewing - Joel on Software:

"Introduction - sound passionate

Question about recent project candidate worked on - sound passionate

Impossible Question - sound passionate | ask questions - gather constraints| out of box approach like lookup services - use any information to arrive at a solution - Get It Done approach (Approach is important to solving - information gathering (asking the right questions) and deriving meaningful information resulting into a probable solution

C Function - again look and improving time and space efficiency (use binary techniques), recursion, caching(memoization) or lazy caching of part computations.

Are you satisfied? - look for bugs in ur own software - be diplomatic but firm with your answer.

Design Question - Ask questions (gather constraints) | seek who are the actors| seek the purpose of
something being designed| seek future constraints| seek how the system is going to evolve | 
capacity planning | seek performance metrics|seek business metrics| seek time and cost metrics

Then proceed to design implementation - seek entities and their relationships such as has-a, is-a, uses-a and cardinality relationships | trim and truncate unnecessary stuff| start bottom up approach

Follow these pointers:


:: Keep it simple

:: Don't over-design

:: Keep it nimble and have the ability to extend as needed

:: Deisgn should be evolutionary - should evolve with change

:: Start bottom - up (identify the objects first and then 

group them to find the inherent relationships between them)

Your design should represent these inherent relationships
such as :

    => has-a, is-a, uses and cardinality relationship

and then further applying creational, structure and behavior patterns

The Challenge - Be passionate and be firm on what you know. Don't give in 
to the challenges which don't approve of your opinion. Stay firm on what you
believe is correct (this is tricky - you have to know u r right)


Do you have any questions?"



Project future?

where do you see this project going in the next 2 years?

Is the project growing? (CTO)

Responsibilities


in the grand scheme of things where do you see this project and where do you see me?

Do you value leadership qualities?

Leadership criteria?



What are your developers role everyday?

How much coding are they doing? Are they implementing new functionality
everyday?


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