SRP tells us that you should only have a single responsibility in a module. ISP tells us that you should not be forced to be confronted with more than you actually need. If you want to use a print() method from interface I, you shouldn’t have to instantiate a SwimmingPool or a DriveThru class for … Read more
I like to state the single responsibility principle this way: “Every thing you write — every module, class, interface, or method, should have one job. It should do the whole job and only that job. Notice that some of these things you write are big (modules), some are small (methods), some are in between (classes), … Read more
(This answer has been rewritten 2013-05-13, read the discussion in the bottom of the comments) LSP is about following the contract of the base class. You can for instance not throw new exceptions in the sub classes as the one using the base class would not expect that. Same goes for if the base class … Read more
I’ve taken a class in college that spent two weeks around design patters, and read the Gang of Four book to no avail. Understanding what each pattern served for and how to use them to fit my problems was very hard for me, a developer that didn’t have much experience in OO programming. The book … Read more
The first thing I noticed was the improper use of the bank account factory. The factory, pretty much as you have it, should be used by the repository to create the instance based on the data retrieved from the data store. As such, your call to accountRepository.FindByID will return either a FixedBankAccount or SavingsBankAccount object … Read more
Seems like what you’re looking for are the Principles of Object-Oriented Design. Summarized from Agile Software Development Principles, Patterns, and Practices. These principles are the hard-won product of decades of experience in software engineering. They are not the product of a single mind, but they represent the integration and writings of a large number of … Read more
The most effective way to break applications is to create GOD classes. Those are classes that keep track of a lot of information and have several responsibilities. One code change will most likely affect other parts of the class and therefore indirectly all other classes that use it. That in turn leads to an even … Read more
Robert Martin has a very good explanation of Interface segregation principle (ISP), in his book “UML for Java Programmers”. Based on that, I don’t think ISP is about an interface being “focused” on one logical, coherent group of things. Because, that goes without saying; or, at least it should go without saying. Each class, interface … Read more
Single Responsibility Principle – A class should have only one reason to change. If you have a monolithic class, then it probably has more than one reason to change. Simply define your one reason to change, and be as granular as reasonable. I would suggest to start “large”. Refactor one third of the code out … Read more
Let’s start with what does Single Responsibility Principle (SRP) actually mean: A class should have only one reason to change. This effectively means every object (class) should have a single responsibility, if a class has more than one responsibility these responsibilities become coupled and cannot be executed independently, i.e. changes in one can affect or … Read more