Class definition Contain the abstract methods. Contain the code for each of its methods. Access specifiers used Public Public, private or protected. Instantiation Cannot be used to declare objects. Class can be instantiated using objects. Interfaces are kind of similar to classes but they contain methods with no code within it. These methods are known as the abstract method which lacks instance variables or the methods are declared without a body. It is essentially used to abstract a class. The interface is defined once and implemented in by several classes and in different ways.
So, when a class implements an interface it is compelled to implement all the methods that the class contains. The methods can also be resolved during runtime using interfaces. An Interface provides abstraction. There is a restriction on Java, it does not enable multiple inheritance and only a single class can inherit another class.
To achieve multiple inheritance, the interfaces are used, so that we can make multiple classes to inherit its properties into a subclass. Inheritance is the concept used to create hierarchical frameworks. The inheritance enables to construct a general class that define properties common to a collection of linked entities, and this general class can be inherited by other classes further including unique properties to its classes.
The terms used in java are superclass and subclass, superclass for the class that is going to be inherited while the class that does the inheriting is referred to as a subclass. Thus, the subclass is said to be the specialized edition of the superclass. D principles and read the book Effective Java. It has good lessons from experienced software engineers. Interfaces are made so that a class will implement the functionality within the interface and behave in accordance with that interface.
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I still have some confusion about this thing. What I have found till now is Similar questions have already been asked here but I was having some other points. Interface is collection of ONLY abstract methods and final fields. There is no multiple inheritance in Java. Interfaces can be used to achieve multiple inheritance in Java. Then why to make interfaces? Improve this question. Community Bot 1 1 1 silver badge. Add a comment.
Active Oldest Votes. There are few use-cases for interfaces: Object effectively has two identities: a Tank is both a Vehicle and a Weapon. What you are looking for are trait like in Scala , unfortunately unavailable in Java. Improve this answer. Tomasz Nurkiewicz Tomasz Nurkiewicz k 67 67 gold badges silver badges bronze badges. Can you please elaborate benefits of using interfaces?
GPSingh: I tried to add few points below Q3. Do you have some further questions? The answer to question two - "they are not" used to achieve multiple inheritance, is contradictory to the answer to question three - "interfaces are kind-of multiple inheritance". This makes it somewhat confusing. In Q1: you said it not used to achieve multiple inheritance but on the Q2: If you said kind of multiple inheritance.
Could you be more specific and clear? I feel like the structure that you've build in your code would be better and more logical with extends-inheritance than with implements-interfacing.
I think it's a rather bad example — Impulse The Fox. If you want a more practical example of when you'd use an interface and when not. Think of writing an app that has to save some data. In the beginning you know you'll want to save the data, and to load it again, but you might be conflicted as to how: Thus you create an IOInterface.
You choose first to write the data to a plain file, and create the FileContext which inherits IOInterface. Then you find out saving it in a SQLite database is actually the thing. Code by addition. A better way would be that animal is the parent class. Monkey and Lion would extend animal.
There would be an interface Swing which monkey implements, an interface Roar which Lion would implement. MobDev here the point was to elaborate that two different classes can have their own different implementation for the same interface's methods. It is mandatory for the classes to override the methods, but they can have different code for implementation. Real World Example A 'real world' example would be the legislation and convention interface surrounding an electrical wall socket in a particular country.
Why use interfaces? You start off by clarifying interface implementation vs concrete inheritance which is a very important distinction. But your latter use of the term interface can be confusing in the real world example. Can something be done to improve clarity? Real world example of what? Interface, Inheritance? The next phrase could lead one to believe that it is an example of an interface, but the example seems like a concrete implementation.
Thanks Steve - you're right, my answer was in need of some TLC. KISS I have searched for days, nay weeks trying to understand interfaces and seem to read the same generic help; I'm not trying to disparage the contributions, but i think the light-bulb just clicked so I'm chuffed : I prefer to Keep It Simple Stupid, so will proffer my new found view of interfaces.
If i have it wrong, then please let others know in follow up comments. I sincerely hope this helps a fellow noob with this difficult principle. Object, ByVal e As System.
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I believe you may mean instance variable instead of interface variable — Steve Buzonas. I will start with a quote: An interface is simply a specification of a set of methods that an object responds to. No, simlpy because there is no multiple inheritance in Java. See above. That's called "implementation inheritance". As you wrote, it's a convenient way to reuse code. But it has an important counterpart: parent classes often define at least part of their subclasses' physical representation.
Actually, inheritance serves also another purpose: Class inheritance combines interface inheritance and implementation inheritance. Questions Q1. Give mutliple types to an object In OOP, one object may have different types. I quote the official Java doc: In addition, Runnable provides the means for a class to be active while not subclassing Thread. You could also think of the Single Responsibility Principle: A class should have only one reason to change.
Inheritance howewer has advantages: It is safe to use inheritance within a package, where the subclass and the superclass implementations are under the control of the same programmers. Bloch, item 16 An example of a class "specifically designed and documented for extension" in Java is AbstractList. An interface declaration can contain method signatures default methods static methods constant definitions. Uses of interface: To define a contract To link unrelated classes with has a capabilities e.
Coming back to your queries: Q1. Refer to " uses of interface " section in my answer. Ravindra babu Ravindra babu Ben Ben 1 1 silver badge 8 8 bronze badges. Quick Practical Short Answer Interfaces are better when you have several years of experience using Multiple Inheritance that have Super Classes with only method definition, and no code at all. Dont rush to use interfaces.
Long Boring Answer Interfaces are very similar, or even equivalent to abstract Classes. If your code has many Abstract classes, then its time you start thinking in terms of Interfaces.
The following code with abstract classes: MyStreamsClasses. And in here lies the answer to question three, and what I feel is one of the greatest strengths of modern OOP: "Code by addition, Not by modification" - Magnus Madsen, AAU That's what he called it at least, and he may have it from some other place.
By making the interface, we can even do the SQLiteContext implementation, and write to a database, SampleApp will never know or care, and when we have written the SQL lite class, we need only make one change to our code: new JSONFileContext ; instead becomes new SQLiteContext ; We still have our old implementations and can switch back to those if the need arises.
Ritesh Singh 65 1 1 silver badge 8 8 bronze badges. Interfaces An interface is a contract defining how to interact with an object. Inheritance Inheritance is an extension of a particular implementation. Composition Composition can be used as an alternative to inheritance. Answers Q1. One of the major benefits of interfaces is to provide separation of concerns: You can write a class that does something with another class without caring how that class is implemented.
Any future development can be compatible with your implementation without needing to extend a particular base class. Steve Buzonas Steve Buzonas 4, 1 1 gold badge 30 30 silver badges 53 53 bronze badges.
Would help if you can go more on the how rather than Interfaces are not inheritance. LBy Thanks for the input. Does that clarify better? The edited answer shows which values the concrete classes inherit from their parents' classes and not from the interface. It is not equal inheritance. It is just similiar. Imagine a system where you use a VolvoXC90 class in other classes. Now, imagine a system where you use a Volvo interface in 10,, classes. Anderson Marques Anderson Marques 6 6 silver badges 11 11 bronze badges.
Programmer 2 2 gold badges 2 2 silver badges 7 7 bronze badges. Dark Drake Dark Drake 1 1 gold badge 8 8 silver badges 21 21 bronze badges. Sign up or log in Sign up using Google. Sign up using Facebook. A class with at least one abstract method is an abstract class. Example of an abstract class is as follows. Assume that there are two abstract classes as A and B. To implement abstract methods of A and B, a new class C is created.
Then class C should extend both A and B. Therefore, should use interfaces. Interfaces can be used to declare methods, but it is not possible to define methods. It is not possible to create an object using interfaces.
Class C should implement all methods in interface A and B. When creating an object of B, it is possible to call both methods sum and multiply. If the programmer wants to restrict using multiply function, it is possible as follows. It is of type A and the memory is allocated as B. It is possible to call sum but cannot execute multiply. This restriction is done using interfaces. Java is a multi-paradigm programming language which supports object-oriented programming. Inheritance and interfaces are related to object-oriented programming.
The difference between inheritance and interface is that inheritance is to derive new classes from existing classes and interfaces is to implement abstract classes and multiple inheritance. You can download PDF version of this article and use it for offline purposes as per citation note. Point, Tutorials. Available here 2. Available here. Her areas of interests in writing and research include programming, data science, and computer systems.
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