design-principles

I have been reading DRY principle.Though it seems so easy but I am having difficulty in understanding how we actually achieve it in any Project be it Web Application or Swing? May be few examples will give me lead and help me in developing my thought process. I have tried to search on Google but could not find any thing suitable. DRY is nothing that requires examples. If you are copying and pasting blocks of code from one method, function or block of code to another, then you are in violation of DRY. Very simply, DRY tells you to move that code into a reusable unit: either into a function or

I have a problem understanding an UML below: Specifically, what is the relationship between PersistentSet and ThirdPartyPersistentSet ? What is the relationship between PersistentObject and ThirdPartyPersistentSet ? Please note that the UML is from Agile Principles, Patterns, and Practices in C# By Martin C. Robert, Martin Micah 2006. Chapter 10 Thanks in advance! The relationship between PersistentSet and ThirdPartyPersistentSet is an Aggregation, which means the PersistentSet contains one or more ThridPartyPersistenSet instances. This is a "weak" relationship, meaning the instances of

I am a huge fan of software design principles such as SOLID and DRY . What other principles exist for OO software design? Note. I’m not looking for answers like "comment your code" but instead looking for OO design principles like the ones discussed by Uncle Bob . A fairly comprehensive list from Wikipedia: http://en.wikipedia.org/wiki/List_of_software_development_philosophies Agile software development Agile Unified Process (AUP) Behavior Driven Development (BDD) Big Design Up Front (BDUF) Brooks's law Cathedral and the Bazaar Code and fix Constructionist design methodology (CDM) Cowboy

My understanding of the Liskov substitution principle is that some property of the base class that is true or some implemented behaviour of the base class, should be true for the derived class as well. I guess this would mean when a method is defined in a base class, it should never be overrided in the derived class - since then substituting the base class instead of the derived class would give different results. I guess this would also mean, having (non-pure) virtual methods is a bad thing? I think I might have a wrong understanding of the principle. If I don't, I do not understand why is

The Interface Segregation Principle (ISP) says that many client specific interfaces are better than one general purpose interface. Why is this important? ISP states that: Clients should not be forced to depend on methods that they do not use. ISP relates to important characteristics - cohesion and coupling . Ideally your components must be highly tailored. It improves code robustness and maintainability. Enforcing ISP gives you following bonuses: High cohesion - better understandability, robustness Low coupling - better maintainability, high resistance to changes If you want to learn more

The Open/Closed Principle states that software entities (classes, modules, etc.) should be open for extension, but closed for modification. What does this mean, and why is it an important principle of good object-oriented design? Specifically, it is about a "Holy Grail" of design in OOP of making an entity extensible enough (through its individual design or through its participation in the architecture) to support future unforseen changes without rewriting its code (and sometimes even without re-compiling **). Some ways to do this include Polymorphism/Inheritance, Composition, Inversion of