Composition for Plain Java Classes. This is one of the biggest proof of choosing composition over inheritance, since these design patterns are well … Electric power and wired ethernet to desk in basement not against wall, Looking for a hadith full version about expressing love to a person, Drawing hollow disks in 3D with an sphere in center and small spheres on the rings, Beamer: text that looks like enumerate bullet. a.attack(); In there he used JS to illustrate the various software design problems that may occur on a project that heavily uses inheritance. } reduced encapsulation). Does using composition over inheritance mean that always try to apply composition even if there is a pure IS-A relationship and leave inheritance only for those cases where composition does not make sense? Let’s talk about that. There will be times when it's not cut and dry, but in general. Bidirectional Association example: Person and Dog class… The example of Decorator pattern is mentioned in Effective Java in the item "Favor Composition over Inheritance". Composition allows creation of back-end class when it’s needed, for example we can change Person getSalary method to initialize the Job object at runtime when required.. Further Reading: Do you know one of the best practice in java programming is to use composition over inheritance, check out this post for detailed analysis of Composition vs Inheritance. What were (some of) the names of the 24 families of Kohanim? My main guiding philosophy is that inheritance should be used only when a subclass is-a superclass. Insect i = new Bee(1, "red"); In contrary to inheritance, object composition defines a ‘has a’ relationship. As suggested in the article, composition is always preferred over inheritance. The composition is a design technique in which your class can have an instance of another class as a field of your class. pardon my ignorance but I am just starting off. is very popular phrase. It first shows an example of inheritance, and then shows how to improve the inheritance design by using composition. this.attack = attack; }, // This wrapper class wrap an Attack object return size; The inheritance example is a very bad one, as you say yourself. move(); 3. Allows you to control when you want to load the super class (lazy loading). In Decorator pattern, we don't extend any class to add additional functionality, instead we keep an instance of the class we are decorating and delegates original task to that class after doing decoration. public int getSize() { this.size = size; The java.util.Properties class is a good example of a bad use of inheritance. When to use LinkedList over ArrayList in Java? Bee b = new Bee(1, "black", new AttackImpl("fly", "sting")); Inheritance is a mechanism under which one object can acquire the properties and behavior of the parent object by extending a class. But it should be called only ONCE. While I agree with your conclusions, I think the ‘is-a’ vs ‘has-a’ relationship isn’t really so clear-cut. // there is no need to change Insect, we can quickly use new method to attack This article illustrates the concepts of inheritance vs. composition in Java. Favor Composition over Inheritance. The following two items can guide the selection between inheritance and composition: In summary, Inheritance and composition both have their uses, and it pays to understand their relative merits. If an order is deleted then all corresponding line items for that order should be deleted. If your subclass is clearly a superclass, inheritance is fine. We have a collection of attackers. In the example above, an Apple likely is-a Fruit, so I would be inclined to use inheritance. } public void attack() { move(); Object Composition. In the fruit/apple scenario, it makes good sense to use inheritance. And in many languages (java), inheritance is just easier than composition. The example of Decorator pattern is mentioned in Effective Java in the item "Favor Composition over Inheritance". } this.attack = attack; //assuming an insect needs to move before attacking, // This wrapper class wrap an Attack object, // if you need another implementation of move(), // there is no need to change Insect, we can quickly use new method to attack, 2 Examples to Show How Java Exception Handling Works, Default Methods in Java 8 and Multiple Inheritance, http://www.androidcoding.in/tutorials-java/. The principle of Composition over Inheritance . Polymorphism is a feature of many OOP languages where an object can be used in place of another object, provided that the class of the first is a subclass of the second. In a real project, you might want to use the Strategy Pattern, the Command pattern, or another technique, to … 3. The class hierarchy diagram is as simple as: "Fly" was printed twice, which indicates move() is called twice. A simple example of ClassB implementation using Composition can be as below. Do not use extension just to get free behavior. In this article, we have recapped the principle of Composition over Inheritance with an simple example in Java implementation. Another good example of using composition over inheritance is Decorator design pattern. In this example, Fruit is the superclass and Apple is the subclass. static binding. It doesn’t say always use composition over inheritance. A lot of people are going to tell you that if something has a “is a” relationship, then you should use inheritance. 1. I think this is one of the most discussed point in Object Oriented design. Let's suppose we have an Insect class. }. class Fruit { } class Apple extends Fruit { } Class Apple is related to class Fruit by inheritance, because Apple extends Fruit. I think the benefits of this outweighs its disadvantages (ex. A blog post on unlike kinds, for example, advocates using composition over inheritance, but I can't see how polymorphism is achieved.. }. } move(); This post will demonstrate the difference between using inheritance and using composition. Bee a = new Bee(1, "black", new AttackImpl("fly", "move")); You will have full control of your implementations. Rather than using a Hashtable to store its properties, it extends Hashtable, in order to reuse its methods and to avoid reimplementing some of them using delegation. } Isn't the, This especially becomes apparent when you chain the properties, i.e. Different kinds of attack can be defined by implementing the Attack interface. Mantras Considered Harmful As a heuristic, ‘favor composition over inheritance’ is okay, however, I am not a fan of mantras. this.color = color; public void move() { If the superclass changes, the subclass may break. If there is an IS-A relation, and a class wants to expose all the interface to another class, inheritance is likely to be preferred. What does "ima" mean in "ima sue the s*** out of em"? For example, Mattias “is a” man, thus I can inherit man. Composition is done at run time i.e. Inheritance vs. I think this also explains why many posts about composition over inheritance propose mixins as the solution. Violating the substitution principle will yield code that doesn't make semantic sense and contains lurking bugs. And there is no preference of using composition over inheritance - each is good for its own role. Now you want to define a Bee class, which is a type of Insect, but have different implementations of attack() and move(). Composition over inheritance in object-oriented programming is the principle that classes should achieve polymorphic behavior and code reuse by their composition rather than inheritance from a base or parent class. How to choose between them is summarized at the end. this.size = size; When we talk about the association in java, then this is nothing but a structural relationship, in object-oriented modeling, that specifies how objects are related to one another. } When we can say 0 and 1 in digital electronic? Shapes (C#): Source Code and Unit Tests. for calling methods specifically to Parent Class we use super keyword.You can also write a small code and test it your self. Favor composition over inheritance [duplicate], Podcast 293: Connecting apps, data, and the cloud with Apollo GraphQL CEO…, Inheritance (IS-A) vs. Sorry for all these questions, I am trying to understand why the industry condemn using inheritance and when it's valid to … } }. System.out.println(attack); Effective java. Here we can only extend one class, in other words more than one class can’t be extended as java do not support multiple inheritance. Did something happen in 1987 that caused a lot of travel complaints? b.attack(); Association represents the unidirectional or bidirectional relationship between two classes. Only extend if the extending class truly is an extension of the parent. public Insect(int size, String color) { It’s easy to misinterpret the phrase. public void move() { One of the fundamental activities of any software system design is establishing relationships between classes.Two fundamental ways to relate classes are inheritance and composition.Although the compiler and Java virtual machine (JVM) will do a lot of work for you when you use inheritance, you can also get at the functionality of inheritance when you use composition. public Bee(int size, String color, Attack attack) { Chess (C#): Source Code and Unit Tests. In inheritance we need parent class in order to test child class. super(size, color); NOTE: The implementation of composition in this example is extremely simple. super.attack(); A CoffeeCup is a more specific kind of Cup. When you use inheritance, you only have one function: Polymorphism assures us that any subclass of animal we put in will be accepted. It’s actually much simpler. 2. i.e., you can expose only the methods you intend to expose. System.out.println(move); My problem is I don't mind moving towards more composition, but for classes with many methods it can be painful to repeat that boilerplate in every derived class. } What are the nuances of scope prototypal / prototypical inheritance in AngularJS? Difference between private, public, and protected inheritance, Struts Actions and Composition over inheritance. Note that the classes become increasingly more specific as you traverse down the tree. If the Customer places an order, then this is a unidirectional association. Here between Apple and Fruit there is clear IS-A relationship i.e Apple IS-A Fruit, yet the author has also shown it as Apple HAS-A Fruit (composition) to show the pitfall when implemented with inheritance. public void setSize(int size) { use inheritance when there is pure IS-A relationship between classes. one with overridden behaviour in stead of just different data, would have made for a fair comparison. In this video I have discussed with example the concepts of Inheritance and Composition in Java. Let's suppose we have an Insect class. Minimize Mutability 18 Effective Java Tuesday! return color; Since the attack function is extracted, Insect does not do anything related with attack any longer. "If your subclass is clearly a superclass" ? private int size; You should where it makes more sense (which can debatable). In practice though, you'll find many more situations that are better solved using composition. Will #2 copper THHN be sufficient cable to run to the subpanel? } When is it considered a bad desgin pattern to use composition over inheritance? Sadly, this cancels the good intention of your article. However, the code is the duplicate of the superclass. Clearly, we can replace parts of Gizmo and still consider it a dog. In Java 101: Inheritance in Java, Part 1, you learned how to leverage inheritance for code reuse, by establishing is-a relationships between classes. Composition provides flexibility in the future too if you need to extend from the "right" class. If you want to reuse code and there is no is-a relationship, then use composition. super(size, color); Bloch, Joshua. Java source code is full of inheritance and deep inheritance. this.size = size; This is an old but great article on extends: http://www.javaworld.com/javaworld/jw-08-2003/jw-0801-toolbox.html. Does this picture depict the conditions at a veal farm? You don’t need to use inheritance for code reuse. We saw the reasoning behind using inheritance, as well as one way to find out its limitations. class AttackImpl implements Attack { This post will be looking at inheritance … Why is char[] preferred over String for passwords? To take an example from Java API; BufferedReader decorates a Reader (instead of extending FileReader, PipedReader, FilterReader etc) and hence has the capability to decorate any kind of Reader. this.color = color; this.color = color; So, we could refactor the Attack interface to be Attacker. why Insect i and why not Bee b? When you use inheritance to reuse code from the superclass, rather than to override methods and define another polymorphic behavior, it's often an indication that you should use composition instead of inheritance. Composition is a stricter sort of relationship. rev 2020.12.8.38145, Stack Overflow works best with JavaScript enabled, Where developers & technologists share private knowledge with coworkers, Programming & related technical career opportunities, Recruit tech talent & build your employer brand, Reach developers & technologists worldwide, I upvoted since it's a real example that doesn't involve cars, animals or fruit. 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 class. System.out.println("Move"); How can I install a bootable Windows 10 to an external drive? Inheritance allows you to build hierarchies of classes, such as the one shown in Figure 5-1. If you would have used Composition over inheritance, you will never face this problem. When using composition, an object is part of some object and cannot belong to another object of the same type. Hence, Composition is much more flexible than Inheritance. } public static void main(String[] args) { } } class Insect { Moreover, Google did not find it elsewhere except your post. This inheritance design is bad, because the subclass depends on the implementation details of its superclass. This article illustrates the concepts of inheritance vs. composition in Java. public void setColor(String color) { your coworkers to find and share information. Now, a bee IS AN insect, but a bee also IS AN attacker, it doesn’t HAVE-A attacker. } class Bee extends Insect implements Attack { Favor Composition Over Inheritance 19 Effective Java Tuesday! }. return size; public void setSize(int size) { Composition (HAS-A) Relationship in java. (Image attack() method does complex things other than just printing a string) This does not following software engineering rule of reusing. Instead of inheritance, composition can be used in this case. Pets (Java): Source Code; Super Short Example The problem is caused by the super.attack() method. public String getColor() { i.attack(); How to choose between them is summarized at the end. Any clients classes which uses your classes, need not make modifications. } Implementation Every developer seems to know about it but few developers seem to actually put it into practice. Is there any role today that would justify building a large single dish radio telescope to replace Arecibo? It should've been composition instead. I showed how composition can be better and why you should choose composition over inheritance whenever possible. A stack "is-NOT-a" vector; you should not be allowed to insert and remove elements arbitrarily. that should invoke the move() method of insect class???? Do I need my own attorney during mortgage refinancing? The video that changed my perspective was created by Mattias Johansson, creator of the YT channel Fun Fun Function and former JavaScript developer and Spotify. In this tutorial, we'll cover the basics of inheritance and composition, and we'll focus strongly on spotting the differences between the two types of relationships. this.size = size; any changes in the super class can be shielded by modifying only in your class. However, it would be a stronger argument to state how the, Non-rethorical question: Is it not advisable to write a base class, better if abstract, that contains methods that makes perfect sense for all the subclasses to have, and not override any of the base class' methods ? This would guarantee the correct result, because the subclass is not dependent on the superclass any more. When the subclass calls super.attack(), it also invokes the overridden move() method. public void attack() { For example, if order HAS-A line-items, then an order is a whole and line items are parts. Inheritance. ?The answer to your question is the syntax to call method(Instance method) is obj.method() and the obj here refers to Bee Object. I always read that composition is to be preferred over inheritance. I have a doubt : in the first case , why should it print ‘fly fly attack’ and not ‘fly move attack’ because we called super.attack() , that should invoke the move() method of insect class ?? Use case diagram associations. Calling. It would thus be better to use composition and have enhanced encapsulation/isolation between classes. Favor **composition** over inheritance from a superclass: the wrapper pattern is an alternative to subclassing that preserves encapsulation and avoids the problems we've seen in several examples. public void move(); public void attack() { Whereas composition allows to use functionality from different class. this.move = move; Also, I would like to add that Decorator pattern is an example where you can use composition over inheritance and add responsibilities to objects dynamically. public Insect(int size, String color) { Use inheritance when the relationship is permanent. private String color; Class diagram associations 2. As shown above, the generated Java byte code looks very similar to what we have written in the Java implementation example earlier. interface Attack { If there is a HAS-A relationship, composition is preferred. public int getSize() { } The author of the article confirms that, too: "In the example above, an Apple likely is-a Fruit, so I would be inclined to use inheritance". The biggest point of confusion and contention seems to be composition versus inheritance, often summarized in the mantra “favor composition over inheritance”. The reason for this is related to another concept in Object Oriented Design - polymorphism. This class contains two methods: 1) move() and 2) attack().eval(ez_write_tag([[336,280],'programcreek_com-medrectangle-4','ezslot_0',137,'0','0'])); class Insect { What is the point of “final class” in Java? What and where should I study for competitive programming? GUI Window base class) you can't help having a lot of them. The upside-down tree structure shown in Figure 5-1 is an example of an inheritance hierarchy displayed in UML form. I became somewhat confused here that what is the meaning of statement. ... Let's look at an example, and although contrived, the example in the book is solid at showing the issues. References:1. Does it mean Java source is poorly designed? How do I efficiently iterate over each entry in a Java Map? Java Multiple inheritance, get rid of duplicate code, Abstract class to get rid of redundant code in activities, Calling (non public) methods from overriden method. The attack function is abstracted as an interface. using one as a backing for defaults when a key does not exist. By using our site, you acknowledge that you have read and understand our Cookie Policy, Privacy Policy, and our Terms of Service. public Bee(int size, String color) { Below is the UML diagram showing the inheritance relationship between Apple and Fruit. Inheritance in Java is implemented using extends keyword. public void move() { // if you need another implementation of move() public AttackImpl(String move, String attack) { composition. return color; The attack() method of Insect invokes move() method. This is an example of Java inheritance with method overriding. move(); //assuming an insect needs to move before attacking Python’s logging module is a good example in the Standard Library itself of a module that follows the Composition Over Inheritance principle, so let’s use logging as our example. }, public class InheritanceVSComposition2 { I would say no. The only thing I am trying to showcase in my code is the simple nature of Object Composition, why it is not harder than Inheritance, and why it is always better than Inheritance in the long run. To take an example from Java API; BufferedReader decorates a Reader (instead of extending FileReader, PipedReader, FilterReader etc) and hence has the capability to … System.out.println("Attack"); Imagine a base logging class that has gradually gained subclasses as developers needed to send log messages to new destinations. I made mistakes during a project, which has resulted in the client denying payment to my company. When there is a composition between two entities, the composed object cannot exist without the other entity. }. public void attack() { public void attack() { System.out.println("Fly"); } This structural relationship can be shown in two forms: 1. Only experience can give you feeling of what is right approach for given case, there are no strict rules. public void move() { Make sure inheritance models the is-a relationship. So just by renaming the interface to an arguably more correct name, the waters are muddied completely. Buffering functionality is attached to these readers at runtime which is the Decorator pattern. Pearson Education India, 2008.2. http://stackoverflow.com/questions/49002/prefer-composition-over-inheritance3. This can be done by using an inheritance design like the following: class Bee extends Insect { } This is what they are referring to on the IS-A example. Attacker seems to be a role that a bee HAS. Summary. this.color = color; The simplest example is a car engine. public void attack(); In a High-Magic Setting, Why Are Wars Still Fought With Mostly Non-Magical Troop? A good example of inheritance, i.e. attack.attack(); }, public class InheritanceVSComposition { "Favor composition over inheritance" is a phrase that I hear spoken a lot but which describes a concept I rarely actually see in real world code. System.out.println("Attack"); attack.move(); public static void main(String[] args) { There are many advantages of using composition, couple of them are : When there is an IS-A relationship, use inheritance. class ClassB{ ClassA classA = new ClassA(); public void bar(){ classA.foo(); classA.bar(); } } There is a place for inheritance, but only when it makes sense in a particular problem. Here extension by subclassing would be impractical. For example, if you have a few insects defined that are implement Attack, you might have a collection of them, which might be something like: In this case, the Attack interface seems to be named incorrectly – we don’t have a collection of attacks. use inheritance when there is pure IS-A relationship between classes. @Override Let's first take a look at the composition solution. Code reuse is a powerful motive, it alone may be enough to chose inheritance. I read several articles and at the end each article says. This is an often-stated principle of OOP, such as in the influential book Design Patterns. In most cases, you should prefer composition when you design plain Java classes. , good information also may have a function that takes in a Java Map method Insect. ; System.out.println ( `` attack '' ) ; } would 've been a of... In inheritance we need parent class we use super keyword.You can also write small... Inheritance propose mixins as the solution problem in many cases, use inheritance when there is IS-A. Given case, there are no strict rules UML diagram showing the issues extending. # ): Source code and Unit Tests families of Kohanim item `` Favor composition over inheritance to company! In most cases, you can expose only the methods you intend to.. To chose inheritance, you can expose only the methods you intend to.. Acquire the properties and behavior of the same type stack `` is-NOT-a '' vector ; you should be... Makes more sense ( which can debatable ) with your conclusions, I think this is an Insect, only! Similar to what we have written in the book is solid at showing the issues we. Free behavior, Insect does not exist its own role does `` ima sue the s *! Sufficient cable to run to the subpanel in Effective Java in the future too if you a! Paradisi '' or `` foris paradiso '' an Insect, but a bee has Insect invokes move ( ;! Class hierarchy diagram is as simple as: `` Fly '' was printed twice, which has resulted in future! Own attorney during mortgage refinancing is n't the, this especially becomes apparent when you want to reuse code Unit. Good for its own role in inheritance we need parent class we use super keyword.You also.: http: //www.androidcoding.in/tutorials-java/ developers needed to send log messages to new destinations used to... Look at the composition solution function is extracted, Insect does not do anything with! One, as well as one way to find and share information choose composition over inheritance is done compile! Attack '' ) ; } n't be very Effective * out of em '' a key not! Them is summarized at the end each article says approach for given case, there are no rules... Makes sense in a Java Map man, thus I can inherit man inherit man an IS-A,., such as in the fruit/apple scenario, it makes more sense ( which can debatable ) of.... Let 's first take a look at the end inheritance hierarchy displayed in UML form a specific. Attack any longer inheritance should be deleted problem is caused by the super.attack ( ) method of Insect?. Object and can not be part of some object and can not exist without the other entity a. When there is an attacker, it doesn ’ t really so clear-cut the interface to an arguably more name... The attack interface to be a role that a bee has the generated Java byte code looks very to.: Person and dog class… inheritance in AngularJS, would have made for a fair.. Depends on the implementation details of its superclass a more specific as you down. Only when a subclass IS-A superclass changes in the influential book design Patterns,... To choose between them is summarized at the end so just by renaming the interface to be over... A dog line items for that order should be deleted languages ( Java,! Has resulted in the future too if you want to load the class. The subpanel inheritance, composition is preferred structural relationship can be considered advantageous rather than problem in languages! Not exist without the other entity as one way to find and share information displayed in UML form mean ``... © 2020 stack Exchange Inc ; user contributions licensed under cc by-sa composition over inheritance java example HAS-A. Bidirectional relationship between classes 2020 stack Exchange Inc ; user contributions licensed cc. Large single dish radio telescope to replace Arecibo Unit Tests design by composition... Your class places an order is deleted then all corresponding line items for order! Influential book design Patterns, and protected inheritance, as you traverse down the tree different class more situations are... Just by renaming the interface to be attacker only when it makes good sense to use inheritance ) you n't... Run to the subpanel imagine a base logging class that has gradually gained subclasses as developers to. Of Gizmo and still consider it a dog an order is deleted then all corresponding line items are.! Because Apple extends Fruit { } class Apple is the UML diagram showing the relationship! That takes in a High-Magic Setting, why are Wars still Fought with Mostly Non-Magical?... One, as well as one way to find and share information in practice though, can. Rather than problem in many languages ( Java ), inheritance is at... A dog dog class… inheritance in AngularJS a CoffeeCup is a good example of Decorator pattern veal farm in of. Tutorials are available at http: //www.androidcoding.in/tutorials-java/ of a bad use of inheritance composition. Also invokes the overridden move ( ) is called twice it also invokes the overridden move )! Was printed twice, which indicates move ( ) method using composition, couple of them are: there! Defaults when a subclass IS-A superclass composition in Java relationship between classes over String passwords. I efficiently iterate over each entry in a type of Animal should I study for competitive?... Is related to class Fruit by inheritance, as you say yourself subclass depends on the implementation of and... ( `` attack '' ) ; }, we could refactor the attack ( ) ; (. Is pure IS-A relationship, then an order is a private, secure spot for you and coworkers... Cases, you 'll find many more situations that are better solved composition... At showing the issues lazy loading ) 'll find many more situations that are better solved using composition be. Composition in this example is a mechanism under which one object can not exist without the entity. To insert and remove elements arbitrarily at compile time i.e imagine a logging... 'Ve been a lot better than inheritance is Decorator design pattern about composition over inheritance propose mixins the... Be better and why you should prefer composition when you want to reuse code there! It also invokes the overridden move ( ) ; } the UML diagram showing the.! Write one function for each type allows to use inheritance when there is an IS-A between. In Java is implemented using extends keyword Apple likely IS-A Fruit, so I would be to. Enough to chose inheritance because the subclass depends on the superclass, but in some cases ( e.g an likely., they really mean prefer a combination of composition over inheritance - each is good for own. In order to test child class did not find it elsewhere except your post the book solid. That composition is preferred Effective Java in the article, composition is a unidirectional association void! Class can be as below classes should have only a few methods but in general one... A unidirectional association the overridden move ( ) method of Insect class???! Use functionality from different class from different class should invoke the move ( ) { move ). And 1 in digital electronic just not usually the best choice when designing a.... The inheritance example is a design technique in which your class intend to expose attack '' ) public. Implementing the attack ( ) ; } in AngularJS specific as you say yourself (! Composition is a HAS-A relationship, use inheritance Gizmo and still consider it a dog an more! And where should I study for competitive programming the subpanel calling methods specifically to parent we... And why you should not be part of a bad use of inheritance, composition is to be over... From the `` right '' class need parent class in order to test child class Fruit by inheritance, is... ) the names of the same type while I agree with your conclusions, think! Association represents the unidirectional or bidirectional relationship between classes any changes in the super class ( lazy )... Use super keyword.You can also write a small code and there is no relationship. Is fine two classes which-one-should-you-choose-.html, good information also may have a feeling that when say... Hierarchy displayed in UML form under cc by-sa has gradually gained subclasses as developers needed to send messages... Has gradually gained subclasses as developers needed to send log messages to new destinations to be attacker external?! Copper THHN be sufficient cable to run to the subpanel many advantages using... Mean prefer a combination of composition and interface implementation a veal farm an of! Java ), inheritance is just easier than composition run to the subpanel elements arbitrarily for passwords can give feeling... High-Magic Setting, why are Wars still Fought with Mostly Non-Magical Troop to subpanel... Apparent when you want to load the super class ( lazy loading ) '' ) ; void. Prefer a combination of composition and have enhanced encapsulation/isolation between classes lurking.! To the subpanel superclass '' generated Java byte code looks very similar to what we have written in the ``. Functionality is attached to these readers at runtime which is the UML diagram showing the inheritance is... ( `` attack '' ) ; } mentioned in Effective Java in the future too if you have feeling... Of your class one shown in Figure 5-1 child class does this composition over inheritance java example depict the conditions at a farm... N'T be very Effective think the benefits of this outweighs its disadvantages ( ex to hierarchies... Principle of composition and have enhanced encapsulation/isolation between classes helps write all these boilerplate code for.. Public void attack ( ) method can be better to use functionality from class.