Tight coupling is when a group of classes are highly dependent on one another. This scenario arises when a class assumes too many responsibilities, or when one concern is spread over many classes rather than having its own class. Loose coupling is achieved by means of a design that promotes single-responsibility and separation of concerns. … Read more
Most answers here focus on OOP but encapsulation begins much earlier: Every function is an encapsulation; in pseudocode: point x = { 1, 4 } point y = { 23, 42 } numeric d = distance(x, y) Here, distance encapsulates the calculation of the (Euclidean) distance between two points in a plane: it hides implementation … Read more
I wrote an article about that: Abstract classes and interfaces Summarizing: When we talk about abstract classes we are defining characteristics of an object type; specifying what an object is. When we talk about an interface and define capabilities that we promise to provide, we are talking about establishing a contract about what the object … Read more
For two objects, Foo and Bar the relationships can be defined Association – I have a relationship with an object. Foo uses Bar public class Foo { private Bar bar; }; NB: See Fowler’s definition – the key is that Bar is semantically related to Foo rather than just a dependency (like an int or … Read more
If you think about the Greek roots of the term, it should become obvious. Poly = many: polygon = many-sided, polystyrene = many styrenes (a), polyglot = many languages, and so on. Morph = change or form: morphology = study of biological form, Morpheus = the Greek god of dreams able to take any form. … Read more
Cohesion refers to what the class (or module) can do. Low cohesion would mean that the class does a great variety of actions – it is broad, unfocused on what it should do. High cohesion means that the class is focused on what it should be doing, i.e. only methods relating to the intention of … Read more
You can find an overview of a lot of design patterns in Wikipedia. It also mentions which patterns are mentioned by GoF. I’ll sum them up here and try to assign as many pattern implementations as possible, found in both the Java SE and Java EE APIs. Creational patterns Abstract factory (recognizeable by creational methods … Read more
Let’s take your example of a Dog and a Cat class, and let’s illustrate using C#: Both a dog and a cat are animals, specifically, quadruped mammals (animals are waaay too general). Let us assume that you have an abstract class Mammal, for both of them: public abstract class Mammal This base class will probably … Read more
When do you choose functional programming over object oriented? When you anticipate a different kind of software evolution: Object-oriented languages are good when you have a fixed set of operations on things, and as your code evolves, you primarily add new things. This can be accomplished by adding new classes which implement existing methods, and … Read more
UPDATE: This question was the subject of an immensely long blog series, which you can read at Monads — thanks for the great question! In terms that an OOP programmer would understand (without any functional programming background), what is a monad? A monad is an “amplifier” of types that obeys certain rules and which has … Read more