what is the difference between abstract class and interface which one should be used when?
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An abstract class permits you to make functionality that subclasses can implement or override whereas an interface only permits you to state functionality but not to implement it. A class can extend only one abstract class while a class can implement multiple interfaces.
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Abstract class in Java is similar to interface except that it can contain default method implementation. ... 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.
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In contrast, an abstract class is anything but an abstract data type. An abstract class is a class that has at least one pure virtual member function. It is not a data type (normally, abstract classes do not contain any data members), nor can you instantiate an object thereof.
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From Java 8, it can have default and static methods also. ... Type of variables: Abstract class can have final, non-final, static and non-static variables. Interface has only static and final variables. Implementation: Abstract class can provide the implementation of interface.
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Type of variables: Abstract class can have final, non-final, static and non-static variables. Interface has only static and final variables. ... Multiple implementation: An interface can extend another Java interface only, an abstract class can extend another Java class and implement multiple Java interfaces.
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Since we have a good understanding of the extends keyword, let us look into how the implements keyword is used to get the IS-A relationship. Generally, the implements keyword is used with classes to inherit the properties of an interface. Interfaces can never be extended by a class.
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The interface body can contain abstract methods, default methods, and static methods. An abstract method within an interface is followed by a semicolon, but no braces (an abstract method does not contain an implementation). ... All constant values defined in an interface are implicitly public , static , and final .
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An abstract class is a class that is declared abstract —it may or may not include abstract methods. Abstract classes cannot be instantiated, but they can be subclassed. When an abstract class is subclassed, the subclass usually provides implementations for all of the abstract methods in its parent class.
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Main difference is methods of a Java interface are implicitly abstract and cannot have implementations. A Java abstract class can have instance methods that implements a default behavior. ... A Java class can implement multiple interfaces but it can extend only one abstract class.
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Following are the notable differences between non-static methods and abstract methods. These methods contain a body. You can use normal method directly. You cannot use abstract methods directly, to use them you need to inherit them and provide body to these methods and use them.
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An interface contains behaviors that a class implements. A class may contain abstract methods, concrete methods. An interface contains only abstract methods. Members of a class can be public, private, protected or default.
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Inheritance is creating a class that derives its feature from an already existing class. On the other hand, polymorphism is an interface that can be defined in multiple forms. Inheritance is implemented on the classes whereas, the polymorphism is implemented on methods/functions.
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Fields are variables that provides the state of the class and its objects, and methods are used to implement the behavior of the class and its objects. Interface: Like a class, an interface can have methods and variables, but the methods declared in interface are by default abstract (only method signature, no body).
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Abstract classes get instantiated indirectly via derived classes. They provide common behaviour and instance state, but signal that more is required and must be provided by derived concrete classes. ... Static classes cannot be instantiated, and any state is at the class level rather than the instance level.
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What are the differences between an event listener interface and an event adapter class in Java? An EventListener interface defines the methods that must be implemented by an event handler for a particular kind of an event whereas an Event Adapter class provides a default implementation of an EventListener interface.
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Abstract class can define constructor. They are more structured and can have a state associated with them. While in contrast, default method can be implemented only in the terms of invoking other interface methods, with no reference to a particular implementation's state.
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By definition you have not to use no interfaces and no abstract classes to use WCF... Interfaces are considered to be the best practice because it enables a wise combination of reuses of the same contract (a class can implement multiple interfaces but can inherit only one class)...