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An abstract method is a method that is declared without an implementation without braces and followed by a semicolon , like this: abstract void sum int a, int b ; Consider using abstract classes if any of these statements apply to your situation: You want to share code among several closely related classes. You expect that classes that extend your abstract class have many common methods or fields or require access modifiers other than public such as protected and private.
You want to declare non-static or non-final fields. This enables you to define methods that can access and modify the state of the object to which they belong. For example, the interfaces Comparable and Cloneable are implemented by many unrelated classes.
You want to specify the behavior of a particular data type, but not concerned about who implements its behavior. You want to take advantage of multiple inheritances. 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. 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. Software Engineering Stack Exchange is a question and answer site for professionals, academics, and students working within the systems development life cycle. It only takes a minute to sign up. Connect and share knowledge within a single location that is structured and easy to search.
I'm defining a class structure for persisting to our cassandra database, and I'm unsure about using a combination of an abstract class and an interface. I have two concrete classes, one for persisting reports and the other for persisting configurations. They both have separate entity classes defined else where that the entityMapper uses. I have read this post which is very similar, but I don't think their example really highlights what I want to know.
My question is: is there a point of having the interface at all? Could I simply define both the save and delete methods as abstract methods in the abstract class itself, and eliminate the interface. I've also realised while typing this up that I could just move both the save and delete implementations into the abstract itself since they do the same thing. But in a case where they each implemented the methods differnetly, is there any benefit to having the interface at all?
Why could I not always use an abstract class over an interface, since it allows you to provide abstract methods that must be implemented in subclasses like an interface , but then also allows you to defining common code implementations between them which interfaces do not allow? First, let's rename the repository and interface, and then we can talk about why creating an additional layer of abstraction the interface is beneficial. It has the word "Cassandra" in it, which ties it to a database vendor.
This is where you should begin coupling your repository classes to a database vendor. The ReportRepository class also has a naming problem. It is tied to a database vendor, yet you need specific methods for reports.
The CassandraReportRepository inherits from an abstract class coupled to a particular database vendor, and this is apparent through how these things are named. The ReportService has a dependency on the ReportRepository interface, not the database vendor specific abstract class or even the database vendor specific concrete class.
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