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Closed 11 years ago.
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Interface vs Abstract Class (general OO)
I want to know the difference between an Interface and an Abstract class ?
I'm so confused about this.
Thanks already.
In an interface you simply define the methods that you are going to implement. In an abstract class you can actually write methods that contain some code. I'm sure this question has been asked a thousand times so look at some of the other posts.
Interfaces define contracts. Abstract classes provide for code reuse. An object interacts with other objects via their contracts (Interfaces). An object shares code with other, related, objects, by inheriting it from an abstract class.
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What is an interface in Java?
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Closed 3 years ago.
Would following sentence in short be correct for beginner to understand what interfaces are about: Interface provides methods of implementing class in abstract way without necessity to apply inheritance.
In one sentence:
An Interface is a contract for implementing classes to provide defined methods (not fields!)
Simple definition of interface :
An interface is just like Java Class, but it only has static constants and abstract method. Java uses interface to implement multiple inheritance. A Java class can implement multiple Java Interfaces. All methods in an interface are implicitly public and abstract.
Before java 8, interface in java can only have abstract methods. All the methods of interfaces are public & abstract by default. But Java 8 allows the interfaces to have default and static methods too.
This question already has answers here:
What is the difference between an interface and abstract class?
(38 answers)
Closed 7 years ago.
So I'm currently reading my java book and it doesn't seem to be to clear on the abstract classes and interfaces. Here is my understanding: Abstract classes are created to basically be the most generic form of a superclass, one of which no instance can be created, and an interface contains methods to be implemented by subclasses? Any help on what I'm missing to these aspects of coding. It would be greatly appreciated, thanks!
(I'm not asking what is different between the two, I just want an understanding of what each is)
Well, all that interfaces do are state required implementation. A contract, if you will, that the inheriting class will implement their own versions of those methods with the same parameters and return values.
Abstract classes are similar, except they can implement generic implementation without requiring the inheriting classes to implement it.
Another difference is, that one class can implement multiple interfaces but only inherit from one possibly abstract class.
That's my understanding of it anyways. Hope I helped!
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Understanding the purpose of Abstract Classes in Java
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I have some questions around abstract classes and their use. I know the basics about them; for example, that they can't be instantiated, they can have concrete and abstract methods, ... But I guess what I wanna know is, what purpose do they serve in life (in software engineering)?
What is the purpose of abstract classes in Java?
Why and when should one use an Abstract class? If you can use a normal class and then inherit it, why would you inherit an abstract class?
How would using abstract classes make our life easier? would it provide better maintainability? more flexibility? ...
btw, I've already looked at some similar questions and answers, including Understanding the purpose of Abstract Classes in Java, but they don't answer my question. I'm more looking for answers that shed light on the philosophy behind the introduction of abstract classes in the first place in Java.
Thanks
An abstract class can be used as a type of template for other classes, and most commonly used for inheritance.
The best example is from the book head first java:
abstract class Animal(){}
then you can extend child class such as: dog, cat, fish.
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When to use an interface instead of an abstract class and vice versa?
(26 answers)
Abstract class vs Interface in Java
(15 answers)
Closed 8 years ago.
I understand the technical difference between the two, but I don't understand why one is better to use than the others? Can anyone give me an example that would help me distinguish an advantage one has over the other?
For example: If I was making an rpg game, and I was working on some healing items. What would the uml diagram look like. Would I be using an interface for items, and then healing items or abstract classes.
When to use interfaces
Interfaces are basically used to inherit the behaviour, as we know interfaces can only have abstract methods. When a class implements that interfaces it has to implement all its abstract methods (unless the class itself is an Abstract class), thus it behaves according to the way interfaces defines.
For example, if you want your class to behave as a Thread. You need to implement Runnable interface and override its run() method.
We need to inherit behaviour of two or more forms.
Interfaces are basically created when we know what to do, but we don't know how to do it. To explain in simpler terms I would say, suppose there are 5 tasks which you know must be done. But there can be different ways to do them. Any class implementing them can do them in any way they wish to. So create an interface and put your methods in them.
When to use Abstract class
We know abstract classes can have both abstract as well as concrete methods.
So same example, if you have 5 tasks to be done but for one task there is one default way to do, so you will wish to define its body and you won't be able to do so in interfaces.
In this case we'll create an abstract class. Put 4 abstract methods and one concrete method, which will be inherited by its child classes directly and they won't need to define it on their own. However if they wish they can override its functionality.
Also keep in mind, a class can extend only one abstract class at a time.
This question already has answers here:
Closed 11 years ago.
Possible Duplicate:
When to use abstract class or interface?
I am a newbie in Java , can anyone please explain a scenario where abstract class will be
useful and interface will not be and vice versa.
I believe in not so complex problems both can solve the issue with equal ease.
Please explain in layman's term and pardon my ignorance!
When we create an interface, we are basically creating a set of methods without any implementation that must be overridden by the implemented classes. The advantage is that it provides a way for a class to be a part of two classes: one from inheritance hierarchy and one from the interface.
When we create an abstract class, we are creating a base class that might have one or more completed methods but at least one or more methods are left uncompleted and declared abstract. If all the methods of an abstract class are uncompleted then it is same as an interface. The purpose of an abstract class is to provide a base class definition for how a set of derived classes will work and then allow the programmers to fill the implementation in the derived classes.