When to use Abstract class and When to use Interface in Java 

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As far as I know an abstract class must include at least one abstract method

When you don't know the implementation and perform common task to do for all use interface.

@@RajuAhmed111 same we can also achieve using abstract class by defining abstract methods only.except multiple inheritance support what is the other advantage of interface.

@@RajuAhmed111 bro please tell me same that abstraction and interface in hospital management system

it is code reuseability bro

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@@SivaReddyJavaTechie Hi Sir, I have one question, is this possible to control a class to access only required methods of an Interface A, A is having test1 and test2 methods, Class B implements A, now I want B can access only test2. Is it possible? (in java 1.7 or 1.8)

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shasudha sudha where is that line?

Save the file after writing that statement..

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Siva - This is called as runtime polymarphism where you have same method signature in both super class and sub class but at runtime sub class method overrides the super class method.

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If you do like this, you have only one e sub class .. If you go for interface you can implement multiple sub class , and java don't support multiple inheritance...so we are going to. Interfaces

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Use Interface - When all the subclasses want to implement their own implementation for all the methods defined in Interface. Use Abstract class - When there is common methods that can be extends to as it is. This will help code reusable and if any sub class want its own implementation then , sub class can override those methods

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Interface provides 100% abstraction in Java. Interface is used to provide as a contract for the implementations. In a system it is possible to have the multiple class having the same method name but implementation might be changed from one sub class to another sub class when you providing the functionality for the methods. Hence using the interface, you provide as a contract for the business. E.g: in the case of JDBC, java provides Statement as interface and it have below methods. 1) public ResultSet executeQuery(String sql) 2) public int executeUpdate(String sql) 3) public boolean execute(String sql) 4) public int[] executeBatch() For Java, it does not matter for which database it has to execute the queries as long as database vendor provides the functionality for the above methods. Also each database(oracle, DB2, mysql) can have their own implementation for executing the queries. Abstract class : Go for abstract class when all sub classes methods having the same functionality of the super class method then it is better you can provides those common methods in the abstract class and which you feel implementation is differ in sub classes declare them as abstract methods so that sub classes can only provide implementation for the abstract methods and other methods can be used as code resuable

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Yes, you can.

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Thanks Jay.

Yes, and you cannot instantiate it either, of course. If you extend a class with an abstract class and not define or provide the implementation for the base class abstract methods then the child class extending it would automatically become abstract.

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Thanks James.

Here is the scenario : If you don't want super class implementation getaddress method in sub class, you can override and get what ever the functionality you want in the subclass method getaddress method. this is based on the requirement, as long as you are happy with the concrete method implementation in super class can be used as it is then no need to override else you have to override it. Hope it is clear now.

Suman - Abstract class is a class which contains at-least one abstract method or if we have any requirement where only sub class need to create object for the super class then you can declare class as abstract so that nowhere possible to create object for abstract class expect using the sub class which extends that abstract class. Thanks for liking the video.

Then Siva why didnt you mentioned that in the video, that means you are sharing half knowledge and some one might get rejected for answering this way in the interview. Please be careful about such things in the future.

Yeah, it think what you are trying to say is that an abstract class may or may not have an abstract method, we don't need to have an abstract method in the abstract class, and it sounds weird as there's no point in that, however, if we mark any method as abstract then we must mark the class as abstract too. @SivaReddy, Nice explanation! The video is really helpful.

Suman Ghimire Abstract class may contain or may not contain abstract method abstract class Test { It will wotk; } Class Test1 { abstract void check();//it will generate error }

Abstract class contain 0 or more abstract method

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