Though both extends and implements keyword in Java is used to implement Inheritance concept of Object-Oriented programming, there is a subtle difference between them. The extends keyword is mainly used to extend a class i. The extends keyword can also be used by an interface for extending another interface.
In order to better understand the difference between extends and implements , you also need to learn and understand the difference between class and interface in Java. Though both are an integral part of application development using the object-oriented methodology, an interface is more abstract than a class hence it is used to define API or contract. On the other hand, a class provides the concrete implementation of the interface i.
Though a class can also be abstract to define a contract, it's the job best done by an interface in Java. Even after Java 8, only multiple inheritances of type and behavior are supported in Java by introducing default methods in Java 8 , but multiple inheritances of the state are still not supported.
If you want to learn more about why multiple inheritances are not supported in Java, see here. This is one of the best and up-to-date courses to learn Java online. What is the meaning of extending a class? A class in Java can extend to another class to become a subclass. When class B extends class A, B becomes subclass child and A becomes superclass parent. A subclass can reuse all the features of the parent class and code reuse is a major reason for extending a class but few understand that more important is the defining relationship which is later leveraged by Polymorphism.
For example, if class B extends class A then a reference variable of type A can hold the object of B, which means A now becomes polymorphic because it can hold both A and B.
This gives birth to a technique of creating flexible software, known as programming for interface than implementation where you always use variables of the parent class or interface to define the core algorithm.
The benefit of doing this is any new class that extends the parent class will have access to that algorithm. This immense power comes by using the extends keyword. You can also read the Head First Design Pattern in Java to learn more about the technique of programming for interface than implementation.
The book is also recently updated to cover Java SE 8. Sine an interface and extends an interface too. Show 3 more comments. Arashsoft 2, 5 5 gold badges 30 30 silver badges 53 53 bronze badges.
CodeClown42 CodeClown42 Derived class " is a " base class type implements : You are implementing a contract. Refer to this question for when to use each of them: Interface vs Abstract Class general OO Example to understand things. Dog can think but Cat does not. These specific capabilities are added to Cat and Dog by implementing that capability.
Man is not an animal but he can Think,Learn,Apply,Climb By going through these examples, you can understand that Unrelated classes can have capabilities through interface but related classes override behaviour through extension of base classes. Community Bot 1 1 1 silver badge.
Ravindra babu Ravindra babu Very well explained. It just clicked. Thanks a bunch! Is that really so? I always thought "has a" refers to having something, possessing it. You could say that cat "has a" climbing ability, but I would say reword your example. Cat "is a" Climber", man "is a" "thinker, learner, climber". Since man "is a" thinker, he can do what a thinker can do.
It is even clearer when working with some protocols - if you have a house, it has a door, but it doesn't implement pushingHandle. It also "is a" MaterialObject, meaning it implements interface for obeying gravity; it doesn't have a "GravityObeyingSkill" or something similar. If Man is a thinker, I will establish relation with extends and not implements.
IS A is standard term used for inheritance. Ravindrababu Many thanks for such an clear explanation. Oliver Charlesworth Oliver Charlesworth k 29 29 gold badges silver badges bronze badges. And extends is also for when you're extending an interface For more details. Priyantha Priyantha 4, 4 4 gold badges 23 23 silver badges 40 40 bronze badges.
If the figures used the correct UML notations hollow triangles this answer would be perfect. Hari Menon Hari Menon You can also extend an interface. A class can only implement one interface. A class can extend several other classes. I believe you've gotten this backwards. A class can implement several interfaces" is the correct statement.
Priyantha 4, 4 4 gold badges 23 23 silver badges 40 40 bronze badges. Ryan Efendy Ryan Efendy 2, 1 1 gold badge 18 18 silver badges 16 16 bronze badges. Great explanation; deserves more recognition. Guru Guru 2, 1 1 gold badge 17 17 silver badges 24 24 bronze badges. Both keywords are used when creating your own new class in the Java language.
This can help to clarify what an interface is, and the conventions around using them. Ravindra babu It could be passed to any method where the Person is required, regardless of having different parent than Person More Small cite So, we can have really different inheritance tree of our class Man. That is really cool stuff Javascript's nice face one of the benefits is the built-in support of the Duck typing see wiki. Small cite: "If it walks like a duck and it quacks like a duck, then it must be a duck.
Also The documentation should help here: Interfaces Extending Classes When an interface type extends a class type it inherits the members of the class but not their implementations. Child object can pretend that it is parent If we were to remove something from the man class for example the walk method we would get the following compile time error: Class 'man' incorrectly implements class 'Person'.
Tags: Typescript Extends Implements. Problem with Visual Studio Code using "react-jsx" as jsx value with create-react-app Parsing error: Cannot read file ' Pandas how to find column contains a certain value Recommended way to install multiple Python versions on Ubuntu Some of the methods are overridden by ArrayList again.
Interfaces are way to enforce a contract in Java. They force the implementing class to provide a certain behavior. To implement an interface, class must use implements keyword.
In Java, we can implement more than one interfaces. In this case, class must implement all the methods from all the interfaces. Look at the ArrayList class declaration one more time. It implements 4 interfaces i. List , RandomAccess , Cloneable and Serializable. It has implemented all the methods in given interfaces.
Similar to previous example, lets create something basic to understand how interface implementations look like.
0コメント