Abstract Class vs Interface

[MUSIC] 0:00 Interfaces and abstract classes can accomplish many of the same goals. 0:05 They also have their own unique objectives. 0:10 If you want to guarantee that specific classes provide specific functionality, 0:12 then an interface is a great tool. 0:17 An interface defines what should happen but 0:20 doesn't define how that needs to happen. 0:22 This is extremely useful when sharing code between projects. 0:25 I don't need to worry about how someone else, or even my past self, 0:29 implements their code, I just need to be able to interact with that code. 0:34 One of the most challenging parts of writing software 0:39 is the mental load of storing all the information about how each piece of code 0:42 interacts with every other piece of code. 0:47 If I make a change in one place, what am I going to break somewhere else? 0:50 Many programming philosophies and 0:55 tools deal directly with minimizing this challenge. 0:57 The key to solving this challenge lies with encapsulation. 1:01 Encapsulation allows us to give control of specific functionalities to 1:05 individual objects, allowing us to focus on just the information needed 1:10 to leverage the functionality each object controls. 1:15 Because my own limited memory no longer has to store the inner workings of 1:20 the entire application, I can more quickly add features and bug fixes. 1:25 This also allows new developers to become productive more quickly. 1:31 Because they do not have to understand the inner workings 1:35 of the entire application all at once. 1:38 By implementing multiple interfaces, I can group functionality 1:42 into smaller parts that can be used throughout my application. 1:46 The limitation of interfaces is that they do not 1:51 actually store any implementation details themselves. 1:54 Each class that implements an interface must write their own methods. 1:59 Changing an interface requires changing every implementing class, 2:04 because there's no default implementation. 2:09 To share implementation details between classes, 2:12 you can harness the power of inheritance, creating a parent or 2:15 super-class from which any number of classes can be extended. 2:20 By declaring the parent class as abstract, 2:25 we prevent that class from being directly instantiated. 2:28 Abstract classes also give us the ability to define abstract methods 2:32 that must be implemented by any extending children. 2:37 The main limitation of an abstract class is the same as any other class. 2:41 You can only inherit from one class at a time. 2:47 I have put together a chart that lays out the similarities and 2:50 differences between these constructs. 2:54 Can it be instantiated? 2:57 Does it allow for multiple inheritance? 3:00 Can you define contractual functions? 3:03 Does it contain implementation details? 3:07 Can you make a change that is shared by everything that uses this construct? 3:10 All methods required to be public? 3:16 Can you define properties? 3:19 Can you define constants? 3:22 Can you override these constants? 3:25 Can you type check for this construct? 3:28 Check the notes associated with this video for a printable version of this chart. 3:31 By combining interfaces and 3:36 inheritance, we can make use of the best qualities of each construct. 3:38