Vector. It is but to refactor an inheritance model can be a big waste of time. In general favour composition over inheritance Prefer composition over inheritance? It will, for the most part, result in more flexible and easier to maintain code. With composition, it's easy to change behavior on the fly with Dependency Injection / Setters. Usually it implies the opposite. Viewed 7k times. I think it’s good advice. In C++, inheritance should only be used for polymorphism, and never for code-reuse. If the client needs access to everything JButton provides (dubious) you now have to create a bunch of boilerplate. Composition over inheritance (or composite reuse principle) in object-oriented programming (OOP) is the principle that classes should favor polymorphic behavior and code reuse by their composition (by containing instances of other classes that implement the desired functionality) over inheritance from a. The tricky part is deciding which to use where. ‘Behavior’ composition can be made simpler and easier. That's why it exists. 5. Cons: May become complex or clumsy over time if more behavior and relations are added. Single inheritance rules out using inheritance for "has-a" relationships like those in the cars example above. The rule of thumb is to use inheritance if A is-a B and to use composition if A is-implemented-in-terms-of B. The popular advice is not "stick to composition" it's "prefer composition over inheritance". You can use an. Share. NET), introducing one inheritance hierarchy automatically excludes you from all other, alternative inheritance hierarchies. Also, if you need to add "additional functionality" to your interface, best option is to create a new interface altogether, following the I in SOLID, which is Interface Seggregation Principle. I have yet to find any major downsides to this approach, works just as I would want multiple inheritance to do. Favour composition over inheritance in your entity and inventory/item systems. Only thing I do not like are all of the “GetComponentByClass” calls and checking if they are Valid before doing anything. Composition is a "has-a". Prefer composition over inheritance? 1 How To Make. It just means that inheritance shouldn't be the default solution to everything. For example, you can define a class called Animal, with attributes like name, age, and. Really getting into duck typing is a bit like having loads of implicit interfaces everywhere, so you don't even need inheritance (or abstract classes) very much at all in Python. The point is, to simply put, always consider composition first before you inheriting a class, if both can do the job, prefer composition over inheritance. For example, I assert that you do not need any of those interfaces. It becomes handy when you must subclass different times in ways that are orthogonal with one another. However, there are cases where inheritance is a more suitable choice, such as when you need to define shared behavior or override base class methods. You want to write a system to manage all your pizzas. Example Problem Let’s say that as part of your language you need to describe an input for a certain transformation. enum_dispatch is a crate that implements a very specific optimization, i. Pros: Allows polymorphic behavior. I think the distinction plays out in having to maintain the number of methods shared by your two classes. You really need to understand why you're doing it before you do it. So, we have established that both composition and inheritance, are essential object-oriented programming techniques. ) Flexibility : Another reason to favor composition over inheritance is its. . React has a powerful composition model, and we recommend using composition instead of inheritance to reuse code between components. A third. The Second Approach aka Composition. You may have already noticed this fact in the code above. Otherwise, release notes and migration documentation are there to help transitioning from one version of an API to another. private inheritance is typically used to represent "implemented-in-terms-of". Favor Composition over Inheritance doesn't say never use inheritance. We create a base class. You can easily create a mock object of composed class for the sake of testing. Like everything in software development, there are use cases for each and trade-offs to make for choosing one over the other. How can we refactor "inheritance code reuse" into composition and still be able to keep a polymorphic approach?. Composition is a "has-a". This way, different responsibilities are nicely split into different objects owned by their parent object. Conclusion. Composition is a "has-a". About; ProductsThis is composition. Mystery prefer composition instead of inheritance? What trade-offs are there for each approach? Press an converse question: when should I elect inheritance instead from composition? Stack Overflow. One principle I heard many times is "Prefer Composition over Inheritance. This being said, and to satisfy your curiosity about inheritance: inheritance is a very special relationship that should mean is-a: a Dog is-an Animal, so it may inherit from it. When an object of a class assembles objects from other classes in that way, it is called composition. 1. But you'll need to decide case by case. In this interview, Erich Gamma, co-author of the landmark book, Design Patterns, talks with Bill Venners about two design principles: program to an interface, not an implementation, and favor object composition over class inheritance. Identify Components and Group them in Logical LayersWhy prefer composition instead of inheritance? What trade-offs have there for jede approaching? And the converse question: when should I choose inheritance instead of composition? Stack Overflow. #include <vector> class B { // incomplete B private: std::vector<int> related_data; }; So naturally, we would maybe start reaching for inheritance at this. This basically states your classes should avoid inheriting. avoids vtable-based dynamic dispatch when the number of trait implementations is small and known in advance. Goを勉強している中で、「Composition over inheritance」という概念が出てきました。ちゃんと理解していなかったので、ここで改めて掘り下げます。 ちゃんと理解していなかったので、ここで改めて掘り下げます。 Communicating clearly with future programmers, including future you. 98 KB; Introduction. Of course, if you have many generic. Interface-based Inheritance. A seminal book. util. So, the way I understand "prefer composition over inheritance" is that inheritance leaks an implementation detail. A good example where composition would've been a lot better than inheritance is java. Inheritance and composition relationships are also referred as IS-A and HAS-A. I prefer to opt-in things to expose as opposed to opt-out. In that case, the following is possible (with Eclipse): Write a class skeleton as follows: class MyClass implements XXXInterface. As for composition over inheritance, while this is a truism, I fail to see the relevance here. You should use interfaces instead of having a class hierarchy. Single inheritance rules out using inheritance for "has-a" relationships like those in the cars example above. Terry Wilcox. I had previously heard of the phrase “prefer composition over inheritance”. Composition is a about relations between objects of classes. This site requires JavaScript to be enabled. Each design pattern will assemble simple classes, unburdened by inheritance, into an elegant runtime solution. Another one is the Composition over Inheritance Principle, which states that you should prefer composition over inheritance when possible, as it gives you more flexibility and modularity. How to compare composition vs inheritance. This is a bit of a muse day. In general composition is the one you want to reach for if you don’t have a strong. Teach. It becomes handy when you must subclass different times in ways that are orthogonal with one another. Go to react. Also, is it not possible to have the generic (isInteger etc) methods implemented in the interface Validator and marked finalGoogle "is a, has a" inheritance and composition for an overview on when to use each. Data models generally follow OOP more closely. Inheritance. Improve this answer. Prefer composition over mixins for complex behaviors: If the desired behavior involves complex composition or multiple interacting components, consider using composition (i. The most common usage of is to implement how a type can be. Don’t use is or similar checks to act differently based on the type of the child. The new class is now a subclass of the original class. In general, you should prefer composition over inheritance. "Inheritance vs 'specification' by fields. Why prefer structure instead of inheritance? About trade-offs are there for each approach? And the converse question: when should I choose inheritance instead of composition? Stack Overflow. In this section, we will consider a few problems where developers new to React often reach for. These docs are old and won’t be updated. I'd prefer composition over inheritance since the classes implementing Validator may not necessarily share an is-a relationship. This principle is a reaction to the excessive use of inheritance when Object Oriented design became popular and inheritance of 4 or more levels deep were used and without a proper, strong, "is-a" relationship between the levels. e. dev for the new React docs. If the base class need to be instantiated then use composition; not inheritance. They are not leaking the internal nature of animals; only. Classes and objects created through inheritance are tightly coupled, changing the parent (or superclass) in an inheritance relationship can cause unwanted side effects on the subclass. The client’s dependency on classes is replaced with interfaces. If inherited is a class template itself, sometimes need to write this->a to. The common explanations of when to use inheritance and composition talk about “has a” and “is a” relationships: "If you have an. Almost everything else could change. 2: Repository Pattern. It’s also reasonable to think that we would want to validate whatever payment details we collect. Both of them promote code reuse through different approaches. Prefer composition over inheritance as it is more malleable / easy to modify later, but do not use a compose-always approach. Conclusion. Share your knowledge with others, earn money, and help people with their career. It's said that composition is preferred over inheritance. Your observation about the matrix of classes you'd have when using inheritance is also on point, and can probably be thought of as a code smell pointing toward composition. g. Composition offers greater flexibility, easier maintenance, and better adherence to the Single Responsibility Principle. In the same fashion, one may think that a ThickBorder is-a special Border and use inheritance; but it's better to say that a Border has-a width, hence preferring composition. However, this additional code is not useless: it informs the reader that a progress bar is used and how it is used. Prefer composition over inheritance. แต่ในการ implement ทั่วไป. but do not shoehorn composition where inheritance is the right answer. You must have heard that in programming you should favor composition over inheritance. The subclass uses only a portion of the methods of the superclass. Follow. Without knowing what both classes do or represent, it is impossible to decide whether one 'is a' subtype of the other, but let me remark that in "Effective Java", Joshua Bloch recommends to prefer composition over inheritance in most situations, since inheritance provides your new class with an interface that may be too large, or out of its. Single Responsibility Principle: Inheritance can lead to classes that have multiple responsibilities, violating the Single Responsibility Principle. Compasition is when a class has an instance of another class. Classes and objects created through composition are loosely coupled, which. Why prefer composition over inheritance? Composition over inheritance is a principle in object-oriented programming that suggests prioritizing the use of composition. On the other hand, country B which was insisting on getting a missile, would still get a missile from the base class. Your first way using the inheritance makes sense. What advantages does composition have over inheritance? Coupling and Cohesion Ideally, the objects in our system have high cohesion (i. That is something we hear over and over again when programming in the object-oriented world, whether it is Java, C♯, JavaScript, it is a concept that is widely spoken of but is never fully understood. In the world of Object-Oriented Programming (OOP) you may have heard the statement 'favour composition over inheritance'. On the other hand, there is the principle of "prefer composition over inheritance". Prefer composition over inheritance as it is more malleable / easy to modify later, but do not use a compose-always approach. Then, reverse the relationship and try to justify it. 905. Inheritance is the mechanism by which a new class is derived from. However when we use composition in Python, we cannot access methods directly from the composed class, and we either re-define these methods from scratch, or access them using chaining. Reference. In fact "Prefer composition over inheritance" is right only for classes not designed for inheritance. Prefer composition over inheritance; To start with, what we can be sure of is that our application needs to collect payment - both at present and in the future. The bridge pattern is an application of the old advice, “prefer composition over inheritance“. I didn’t actually need any interfaces because the character is not interacting with the Actors directly. The Bridge pattern is an application of the old advice, “prefer composition over inheritance”. It was first coined by GoF. This basically states your classes should avoid inheriting. 1. They are absolutely different. If you limit the usage of classes, then you’re getting rid of a whole class of design problems. Tagged with tutorial,. One of the issue with inheritance is when you get a diamond structure. The car has a steering wheel. These docs are old and won’t be updated. Prefer composition over inheritance? 1242 What is the difference between public, private, and protected inheritance? 83 How do I implement a trait I don't own for a type I don't own? Related questions. So in this case, good practice is using inheritance and it allows also to respect the DRY principle. JimchaoTry reading through a few answers on Prefer composition over inheritance? As a rule of thumb try out this: if inheritance would result in more than 3 levels of hierarchy, use composition if you have something that matches the strategy pattern, use inheritance always prefer composition (try it first)As the saying goes: prefer composition over inheritance. Inheritence uses the java compiler's type system to implicitly include code from elsewhere, with delegation you explicitly implement the callout. Inheritance should never be about creating a class for each noun, no matter how nice it looks. I have written about the drawbacks of inheritance in the past, and the notion that we should “prefer composition over inheritance” is well-known. Prefer composition over inheritance if you do not need to inherit. In this case, MasterChecker (correctly) composes the various concrete checkers, as your advice recommended. Person class is related to Car class by compositon because it holds an instance of Car class. This might mislead to think that there is a relation between these two different concepts: Inheritance is about a relation between classes. Using interfaces and composition not only makes our code more modular but. 3. That means that insteed of making use of inheritance, we’ll make our UIViewController contain / be composed of inner classes that provide the behavior. There are two benefits of inheritance: subtyping and subclassing Subtyping means conforming to a type (interface) signature, ie a set of APIs, and one can override part of the signature to achieve subtyping polymorphism. This is where the age-old design pattern of composition over inheritance comes into the picture. Some reasons: The number of classes increases the complexity of the codebase. Inheritance. Composition: Composition is the technique of creating a new class by combining existing classes. readable) code, because you don't have complexities of overrides to reason over. If The new class is more or less as the original class. Prefer composition over inheritance as it is more malleable / easy to modify later, but do not use a compose-always approach. Default methods do not change this. e. Improve this answer. Prefer composition over inheritance? Sep 10, 2008. – Blake. Trying to hide the blank look on. Composition works with HAS-A relationship. Taking a mantra like "favour composition over inheritance" out of context and using that as an unbending rule not only goes against that philosophy but highlights the dangers of reducing sound advice to the level of soundbites. If this instruction is followed, one of the biggest features of inheritance is irrelevant: inherited. Yes, (novice) developers need to be urged away from overusing inheritance, but that does not invalidate that there are use cases for inheritance. Share. Hello proggit, I've heard from quite a few places lately to prefer composition to inheritance (last time was from…Sử dụng Composition để thay thế Inheritance. Inheritances use when Portfolio A is a type of List but here it is not. Inheritance is a way of reusing existing code and creating hierarchies of classes that share common features. With composition, it's easy to change behavior on the fly with Dependency Injection / Setters. There are however a number of projects around that can automate this either at compile time (via a pre-processor) or at runtime eg jmixin. Remember the LabelledCheckBoxwe built above. Every single open source GUI toolkit however uses inheritance for the drawn widgets (windows, labels, frames, buttons, etc). Composition is a good substitute where interfaces are inappropriate; I come from a C++ background and miss the power and elegance of multiple inheritance. 0. Use inheritance over composition in Python to model a clear is a relationship. Prefer composition over inheritance. I would still prefer composition to inheritance, whether multiple or single. This idea of keeping internal/private state is nice and you’ll probably miss it if you entirely get. The point in the comments about using interfaces for polymorphism is well made. In general, you should prefer composition over inheritance. Because of everything that dtryon and desigeek have said and also because in your case Inheritance looks unnatural + it will make all your layers tightly coupled and will hardly limit making of any amends to source code. Others: 1. In Rust, it is possible to implement. 繼承(Inheritance) 是實現代碼重用的常見方法 但他並非是唯一的工具 用的不好的話 會使你的. Normally I prefer composition over inheritance, but given that this ensures a consistent set of IDs and allows for a common stream for a limited number of types, I'm not too sure why it wouldn't. Favoring Composition over Inheritance is a principle in object-oriented programming (OOP). Composition and inheritance are two ways that you can use to build an object. 4,984 2 2 gold badges 24 24 silver badges 36 36 bronze badges. In our case, we could imagine a BurgerMenuManager class that provides all the needed methods to setup the burger menu icon and interact with it,. I'm currently reading 'Head first design patterns' and I already have a few questions on the first chapter of the book. #### Objectives + Subclassing & inheritance: superclass inheritance is the source of several problems that we'll examine in this reading. I have read some discussions where some people made the point that extending widgets may make sense in certain scenarios. Pretend you own a pizza shop. In this article, I discussed why you should prefer composition over inheritance, looked at the repository and DTO patterns, and compared two options for initializing lazily fetched associations in the business layer to avoid the Open Session in View anti-pattern. It just means that inheritance shouldn't be the default solution to everything. That only means inheritance should be handled with care because it comes at a cost, not that it isn't useful. If The new class is more or less as the original class. Với nguyên lý Composition over Inheritance ta gom các phương thức chung vào một đối tượng riêng sau đó thực hiện tham chiếu các đối tượng này vào đối tượng mới được khởi tạo. In this tutorial, we’ll explore the differences. This isn't something you can follow without thinking about it. Inheritance is an is-a relationship. I want light structures on my brain, which I could overlook easily. Refer to this related SE question on pros of inheritance and cons of composition. , if inheritance was implemented only to combine common code but not because the subclass is an extension of the superclass. In this article, we learned the fundamentals of inheritance and composition in Java, and we explored in depth the differences between the two types of relationships (“is-a” vs. 2. This will prevent B from being used as an instance of A where this is not appropriate. My question was not a debate about whether to prefer composition over inheritance, or the other way around, as you seem to have taken it. g. The “knock-on” effect is an integral part of OOP; if animals breathe, then it is expected that dogs, cats, humans,. " What benefits was it giving you in this case? I would avoid blindly following "prefer composition over inheritance" like it's gospel. Pros: Maps well to non-oop scenarios like relational tables, structured programing, etc "prefer composition over inheritance" is not a braindead rule saying one should avoid inheritance under all circumstances - that would miss the point of that recommendation, and would be nothing but a form of cargo-cult programming. What I think is there should be a second check for using inheritance. eg:Why prefer composition instead of inheritance? What trade-offs were there to jeder approach? And the converse question: when should I choose inheritance instead of arrangement? Stack Overflow. Prefer composition over inheritance? Have a look at the example in this documentation link: The example shows different use cases of overriding by using inheritance as a mean to achieve polymorphism. Inheritance is known as the tightest form of coupling in object-oriented programming. Inheritance can get messy. In any case, describing a sentence prefixed with the word 'prefer' as 'pithy' seems out of place. In computer science classes you get to learn a ton about. So the goose is more or less. Oct 20, 2021 at 19:20 | Show 4 more comments. This is the key reason why many prefer inheritance. Use composition instead implementation inheritance and use polymorphism to create extensible code. Generally it is said, Favor Composition Over Inheritance, as it offers many advantages. if you place all the information inside. You still get code reuse and polymorphism through it. I believe it could be helpful to take a look at prefer-composition-over-inheritance SO-topic. A good example where composition would've been a lot better than inheritance is java. So let’s define the below interfaces: When I first learned object-oriented programming, I saw inheritance as a useful way for objects to share functionality. Use inheritance over composition in Python to model a clear is a relationship. Has-a relationship will therefore almost always mean composition. That makes me think that everything in Dart is composition and I also was told that we can think that everything in. So the goose is more or less. Here I would like to give one such example to demonstrate why composition, in many cases, is preferable to inheritance. In this course, we'll show you how to create your first GraphQL server with Node. We therefore suggest to prefer composition (=delegation) over inheritance where this is possible. I had previously heard of the phrase “prefer composition over inheritance”. For composition can probably be done by c++20 concepts somehow, not sure. Good article, such programming principle exists “prefer composition over inheritance”. Given that the SOLID principles offer more maintainability and extensibility to your project, I'd prefer interfaces over inheritance. Antipattern: inheritance instead of composition. You still get code reuse and polymorphism through it. In the implementation of this pattern, we prefer composition over an inheritance – so that we can reduce the overhead of subclassing. So now for the example. So here are the benefits of inheritance: Unlike composition, you can pass the subclass into functions expecting the parent class. The new class inherits all public and protected properties and methods from the parent class and can then add its own new ones. Similarly, a property list is not a hash table, so. attr_of_{a,b} gives you an attribute of A or B too (same caveat as with methods). + Composition & delegation: a commonly-used pattern to avoid the problems of subclassing. Inheritance makes change harder because the functionality is spread over many generations (parent - child generations). That said, I definitely do also use. In the answer to this question and others, the guidance is to favor composition over inheritance when the relationship is a "has-a", and inheritance when "is-a". At first, it provided dynamic polymorphism. If an object contains the other object and the contained object cannot. 8. prefer composition over inheritance) object composition can be used to implement associations; Every OOP languages provides composition. As you know, each layer in the viper module has an interface. See more1436. Composition at least you can freely refactor if you need to. If it is there use inheritance. most OOP languages allow multilevel. Despite these downsides, I intend to show you that inheritance is not something to be avoided like the plague. Inheritance and Composition are, in a vacuum, equally useful. Normally you don’t want to have access to the internals of too many other classes, and private inheritance gives you some of this extra power (and responsibility). You can easily create a mock object of composed class for the sake of testing. It’s time to make good on our promise to use the dependency inversion principle as a way of decoupling our core logic from infrastructural concerns. There’s no need to prefer composition over inheritance outright. Much like other words of wisdom, they had gone in without being properly digested. It very quickly becomes a tree that reaches out to all different directions. If it "has a" then use composition. prefer composition over inheritance ,and so on known articles about the abuse of inheritance. Rob Scott Rob Scott. You do multiple inheritance of interface in Java like this: public interface Foo { String getX (); } public interface Bar { String getY (); } public class MultipleInterfaces implements Foo, Bar { private Foo foo; private Bar. Here are some examples when inheritance or delegation are being used: If. dead_alchemy • 14 hr. Like you, I tend to favor composition over inheritance. There are certain things that do require inheritance. You need to be precise: Java allows multiple inheritance of interface, but only single inheritance of implementation. Composition can be denoted as being an "as a part" or. Is initially simple and convenient. Conclusion. Follow. 4. เรา. For instance. Summary. Inheritance is tightly coupled whereas composition is loosely coupled. util. Much like other words of wisdom, they had gone in without being properly digested. The new class has now the original class as a member. In this case composition can be a better solution because it allows you to avoid the ambiguity and unexpected behavior. Let’s take a single design problem and watch how this principle works itself out through several of the classic Gang of Four design patterns. Thus, given the choice between the two, the inheritance seems simpler. e. Inheritance is more rigid as most languages do not allow you to derive from more than one type. Although it is not suited to all software designs there are situations where it is difficult to deny it's utility over interfaces, composition and similar OO techniques. This means that modifying the behavior of a superclass might alter the behavior of all its. class Car may have an Engine member (composition), but may be (i. However, in object-oriented design, we often hear the advice to prefer composition over inheritance to achieve polymorphism and code. Assume your class is called B and the derived/delegated to class is called A then. Is-a relationship CAN mean inheritance is best, but not always. e. Inheritance is limited to a single parent class (and ancestors) but it can sometimes be non-obvious where your code is going; delegation is less elegant, but you can bring in functionality from. @Steven, true, but I am just trying to see if there are ways to prefer composition over inheritance since I don't need most of the low level database API. Composition has always had some advantages over inheritance. composition in that It provides method calling. Composition over inheritance (or composite reuse principle) in object-oriented programming (OOP) is the principle that classes should achieve polymorphic behavior and code reuse by their composition (by containing instances of other classes that implement the desired functionality) rather than inheritance from a base or parent. And in Ruby people constantly forget that modules == multiple inheritance -_solnic_. ” Design Patterns: Elements of Reusable Object-Oriented. You do composition by having an instance of another class C as a field of your class, instead of extending C. Share. Follow edited Jan 2, 2009 at 5:36. 8. To understand why " prefer composition over inheritance", we need first get back the assumption omitted in this shortened idiom. Please -- every fourth word of your post does not need to be formatted differently. In object oriented programming, we know about 4 well-known concept of object oriented programming as abstraction, encapsulation, inheritance, and. Composition is fundamentally different from inheritance. Composition is a “has-a” relationship, used to design a class on what it does. Official source : flutter faq. For this I have made some classes: The Image class that contains an image that. I do not agree with you. Nowadays, notion of composition over inheritance is quite widely accepted. Inheritance doesn’t have this luxury. Composition makes change easier because the functionality sits in the place you expect. When any of the methods draw, collide or update need to do their function, they have access to to the. “Favor composition over inheritance” is a design principle that suggests it’s better to compose objects to achieve polymorphic behavior and code reuse rather than inheriting from a base class. Why should I prefer composition over inheritance? (5 answers) Closed 8 years ago. This chapter introduces the 'prefer composition over inheritance' design principle, by explaining the 'Strategy-Pattern'. React recommends use of Composition over Inheritance, here is why. If you want the object to use all the behavior of the base class unless explicitly overridden, then inheritance is the simplest, least verbose, most straightforward way to express it. Erich Gamma lept onto the software world stage in 1995 as co-author of the best-selling. If you are in total control, you can build entire systems using interfaces and composition. Teach. Inheritance is one of the four major concept of OOP, where a class known as sub/child class achieve the behavior of another class known as parent/super class by inheriting it. Inheritance is among the first concepts we learn when studying object-oriented programming. Here’s an example that illustrates the benefits of composition over. Conclusion. Hopefully it has two wings. Composition is still an OOP concept. Use bridge. The recommendation to prefer composition to inheritance does not mean "never ever use inheritance". There are several other questions like that out there, most of which got negative votes. I think above quote easily explains what I. If you don't require components to be added/removed dynamically to/from your entities, inheritance can be used to define entities (in languages with multiple inheritance). “has-a”). Composition: Composition is the technique of creating a new class by combining existing classes. The implementation of bridge design pattern follows the notion to prefer Composition over inheritance. 3. But inheritance comes with some unhappy strings attached. It's also known as "has-a" relationship. Makes a lot of sense there. The primary issue in composition vs inheritance is that the programming world has begun to think of these two concepts as competitors. Author’s Note: PLEASE DONT FORGET TO READ PART 2 – PREFER COMPOSITION OVER INHERITANCE! – It describes the alternative! It’s what the Gang of Four intended when they made Design Patterns. There's also an efficiency reason to prefer inheritance over composition -- overriding costs nothing (assuming no super call), while composition costs an extra INVOKEVIRTUAL. It's an existential type: a concrete static type. Summary. But make no mistake- inheritance of multiple interfaces is. But this brings certain challenges such as subclass adherence to base class implementations, difficulty in changing the base class over time, and increased coupling. The recommendation to prefer composition over inheritance is a rule of thumb. - Wikipedia. In general, composition (which is implemented by Strategy) as a way of logic reuse is preferred over inheritance. The car is a vehicle. That is, when both options are viable, composition is more flexible down the line. ago.