However with Java 8 default methods in interfaces, Interface and Abstract class are almost same. I feel like the Person, Employee relationship is better represented by an interface rather than an abstract class because a Person can be an Employee but it is not a necessity.
A person can be more than one thing therefore A Person should implement an interface called Employee because they can also be something else like a manager or a supervisor.
So Person has to be superclass. With Java 8 interface default and static methods, there is not much difference between abstract class and interface. What is changeName? Now suppose you have 3 databases in your application. Then each and every implementation for that database needs to define the above 2 methods:. Then the above would not be a good approach. Now in each child class, we only need to implement one method — the method that is database dependent.
Tried my best to make you understand. Hi Pankaj, Can u please tell me where we can use interfaces and abstract classes in realtime,could you please give me in realtime example. Abstract Classes cannot be instantiated. Let us say we have got an abstract class absClass with one unimplemented abstract method doSayHello.
When we implement doSayHello method in the curly brackets, we are doing it under the pretence that we are extending an unnamed class but not by instantiating the abstract class itself.
Abstract class can contain Constructor, if we cannot create an instance what is the use of this constructor. Yes, Abstract classes can have constructors unlike Interfaces. However we cannot directly instantiate an Abstract class to create an instance. The purpose of the Abstract class constructors we can have multiple abstract class constructors with different arguments is to initialize the final variables from subclasses kind of lazy initialization.
If yes then what is the use of making a method abstract in abstract class. You should have a concrete class extending the abstract class and provide implementation of abstract methods, you can also have anonymous class implementation. There is no problem in fact. SubClass extends MyAbstractClass. Hence, definedMethod will also be available in MyAbstractClass.
This is is not showing parameter value. There are two classes person and Employee. You have created the object of person class. Is it ok? Methods of a Java interface are implicitly abstract and cannot have implementations. A Java abstract class can have instance methods that implements a default behaviour. Variables declared in a Java interface are by default final. An abstract class may contain non-final variables.
Members of a Java interface are public by default. A Java abstract class can have the usual flavours of class members like private, protected, etc.
An interface can extend another Java interface only, an abstract class can extend another Java class and implement multiple Java interfaces. Your email address will not be published. Next Interface in Java. Pankaj I love Open Source technologies and writing about my experience about them is my passion. Follow Author. Comments Priyanka says:. September 26, at am. April 8, at am.
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Zabuzard AlexandraC AlexandraC 3 3 gold badges 6 6 silver badges 15 15 bronze badges. What do you mean "belong to"? A concrete class extending the abstract class has to implement all the unimplemented methods in the hierarchy, wherever they may come from.
I am not sure what your question actually is at this point. Could you show some code snippets that you compiled and ran showing what is actually confusing you? Another big difference is that you can implement multiple interfaces but only extend a single class. In both cases a class has to implement the methods as soon as it isn't abstract.
Your question boils down to this: Should abstract class A be of type I which is the interface. As an example: If any implementation of some abstract class should be closeable, it should implement java. Otherwise it should not. Add a comment. Active Oldest Votes. You either implement them in the abstract class or you leave them abstract , but then some of your more concrete children need to implement it. Improve this answer.
Zabuzard Zabuzard Do you know by chance if this same rule applies for C? Azazel I am not a C developer but the languages are very similar. That said, which particular rule are you talking about - the answer covers a lot of aspects. In Java, a class can only inherit from one class, but can implements multiple interfaces.
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Class Abstraction PHP has abstract classes and methods. Just one more time, in the simplest terms possible: An Interface is like a protocol. It doesn't designate the behavior of the object; it designates how your code tells that object to act. An interface would be like the English Language: defining an interface defines how your code communicates with any object implementing that interface.
An interface is always an agreement or a promise. When a class says "I implement interface Y", it is saying "I promise to have the same public methods that any object with interface Y has".
On the other hand, an Abstract Class is like a partially built class. It is much like a document with blanks to fill in. It might be using English, but that isn't as important as the fact that some of the document is already written.
An abstract class is the foundation for another object. When a class says "I extend abstract class Y", it is saying "I use some methods or properties already defined in this other class named Y".
The interface is an agreement to have a specific set of public methods for your class. You would have your class extend an abstract class if you or someone else wrote a class that already had some methods written that you want to use in your new class.
These concepts, while easy to confuse, are specifically different and distinct. For all intents and purposes, if you're the only user of any of your classes, you don't need to implement interfaces.
Here's an example that helped me with understanding abstract classes. It's just a very simple way of explaining it in my opinion. It tastes like an apple. Now I give you a fruit. Well, it doesn't make much sense, so you shouldn't be able to do that.
This is accomplished by making the Fruit class abstract as well as the eat method inside of it. Also, a note. An abstract class is just like an interface, but you can define methods in an abstract class whereas in an interface they are all abstract. Abstraction and interfaces are two very different tools.
The are as close as hammers and drills. Abstract classes may have implemented methods, whereas interfaces have no implementation in themselves. Abstract classes that declare all their methods as abstract are not interfaces with different names. One can implement multiple interfaces, but not extend multiple classes or abstract classes. The use of abstraction vs interfaces is problem specific and the choice is made during the design of software, not its implementation.
In the same project you may as well offer an interface and a base probably abstract class as a reference that implements the interface.
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