Why abstract class is used

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Over 2 million developers have joined DZone. When to Use Abstract Class and Interface. Abstract class in Java is similar to interface except that it can contain default method implementation. An abstract class can have an abstract method without body and it can have methods with implementation also. An abstract class is mostly used to provide a base for subclasses to extend and implement the abstract methods and override or use the implemented methods in abstract class.

Notice that work is an abstract method and it has no-body. Here is a concrete class example extending an abstract class in java. Note that subclass Employee inherits the properties and methods of superclass Person using inheritance in java. Also notice the use of Override annotation in Employee class. Read more for why we should always use Override annotation when overriding a method. If I missed anything important, please let us know through comments. A concrete example of an abstract class would be a class called Animal.

You see many animals in real life, but there are only kinds of animals. Since Is Dead is abstract, each animal must implement it…. By using the static keyword we can access the concrete methods in the abstract class. Can any one tell without using the static how can we access the concrete methods in the abstract class?

Java Abstract class is used to provide common method implementation to all the subclasses or to provide default implementation. The subclass of abstract class in java must implement all the abstract methods unless the subclass is also an abstract class.

If Class3 extends abstract Class2 and abstract Class2 extends abstract Class1, then Class3 should implement all the abstract methods of Class1 and Class2. Class 2 need not implement methods of Class1 since Class2 is also abstract. It was a wonderful recap of what i learned java docs from various resources in internet. Thanks for covering entire picture of core java. God bless you!! While doing some editing, I mistakenly deleted changeName method from Person class, I have corrected it. I want to know the sole purpose of Abstract Class other than its providing Data hiding and forces the programmer to implement all the methods in Abstract class.

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. Note: Abstraction can also be achieved with Interfaces , which you will learn more about in the next chapter.

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