Can you instantiate an abstract class in java

Labels: core java , core java interview question answer. Anonymous March 12, at AM. Anonymous May 4, at PM. Newer Post Older Post Home. Subscribe to: Post Comments Atom. GraphicObject also declares abstract methods for methods, such as draw or resize , that need to be implemented by all subclasses but must be implemented in different ways. The GraphicObject class can look something like this:. Each nonabstract subclass of GraphicObject , such as Circle and Rectangle , must provide implementations for the draw and resize methods:.

In the section on Interfaces , it was noted that a class that implements an interface must implement all of the interface's methods. It is possible, however, to define a class that does not implement all of the interface's methods, provided that the class is declared to be abstract.

For example,. In this case, class X must be abstract because it does not fully implement Y , but class XX does, in fact, implement Y. An abstract class may have static fields and static methods. You can use these static members with a class reference for example, AbstractClass.

All rights reserved. Hide TOC. Interfaces and Inheritance. 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. 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.