why abstract class in java?
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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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The main difference between abstract class and final class in Java is that abstract class is a class with abstract and non-abstract methods and allows accomplishing abstraction, while final class is a class that restricts the other classes from accessing its data and methods.
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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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Yes, an abstract class can have a constructor in Java. You can either explicitly provide a constructor to abstract class or if you don't, the compiler will add default constructor of no argument in abstract class. This is true for all classes and it also applies to an abstract class.
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['Frequent use of code written once, i.e. code reusability.', 'One superclass can be used for the number of subclasses in a hierarchy.', 'No changes to be done in all base classes, just do changes in parent class only.', 'Inheritance is used to generate more dominant objects.']
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Interface is collection of ONLY abstract methods and final fields. There is no multiple inheritance in Java. Interfaces can be used to achieve multiple inheritance in Java. One Strong point of Inheritance is that We can use the code of base class in derived class without writing it again.
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The key technical differences between an abstract class and an interface are: Abstract classes can have constants, members, method stubs (methods without a body) and defined methods, whereas interfaces can only have constants and methods stubs. ... This is because interfaces cannot define any implementation.
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These two are quite different: Default methods are to add external functionality to existing classes without changing their state. And abstract classes are a normal type of inheritance, they are normal classes which are intended to be extended.
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The implements keyword is used to implement an interface . The interface keyword is used to declare a special type of class that only contains abstract methods. To access the interface methods, the interface must be "implemented" (kinda like inherited) by another class with the implements keyword (instead of extends ).
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Abstract methods can be either public, protected or default access (package visible). Unlike interfaces abstract classes can contain fields that are not static and final. *Abstract classes can have private methods, but not abstract private methods.
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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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An abstract class is designed to be inherited by subclasses that either implement or override its methods. In other words, abstract classes are either partially implemented or not implemented at all. ... An abstract class can have constructors—this is one major difference between an abstract class and an interface.
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Class Abstraction ¶ PHP 5 introduces abstract classes and methods. Classes defined as abstract cannot be instantiated, and any class that contains at least one abstract method must also be abstract. ... This also applies to constructors as of PHP 5.4.
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Concrete class in Java. A concrete class is a class that has an implementation for all of its methods. They cannot have any unimplemented methods. It can also extend an abstract class or implement an interface as long as it implements all their methods. It is a complete class and can be instantiated.
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An abstract class is a way to achieve the abstraction in C#. An Abstract class is never intended to be instantiated directly. ... Like a class, Interface can have methods, properties, events, and indexers as its members. But interfaces will contain only the declaration of the members.
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There are two kinds of classes in c++. They are absolute class and concrete class.
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Yes, an abstract class can have a parameterized constructor. This will then be used by the subclasses that extend the abstract class.