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So let's get started by learning about abstract classes and abstract methods and abstract class as the

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name suggests is a class that is too abstract which means that it is too generic to be instantiated

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.

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In other words it is not concrete enough to be instantiated on includes one or more methods for which

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it is not possible to provide any implementation even though it is not intangible.

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The class still plays an important role but defining a common protocol for all its subprocess so it

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defines a contract and hence can be used polymorphically on an abstract that is defined by simply inserting

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the key word abstract in the class declaration that the compiler ensures that the class cannot be instantiated

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like an abstract last and abstract method also involves inserting the key word abstract in the method

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declaration an abstract method will not have any body that is normally braces and it simply ends with

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that semicolon and its implementation will be provided by subprocess.

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That is a MUST be overridden.

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It also means that an abstract muttered cannot be declared as nothing.

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And that's because we know that static methods cannot be overridden.

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So an upstart class has no use unless it is extended.

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It may exist though defined only static members but that cannot be the only purpose of its existence

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and it would also be very confusing.

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So with an abstract class it is the instances of its subclasses which are doing the real work at runtime

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.

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Now let's look at some specifics.

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We cannot have an abstract method in a non abstract us.

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So if there is even one abstract method then the class must be abstract to us.

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In addition to abstract an abstract class may also contain one or more concrete methods that is methods

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with implementations.

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Not that an abstract class need not have any abstract methods but that is not typically done.

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It would be very confusing to have an abstract class without any abstract methods.

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So we know that implementation for abstract methods then be provided in subclasses.

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However a subclass itself can also be declared as abstract.

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That is it would be an abstract supperless and in this case that subclass doesn't have to override an

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inherited abstract method.

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It doesn't even have to really clear that inherited abstract matter.

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It means that some other subclass don't.

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The inheritance but would be expected to provide an implementation for that method.

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It can do it all right.

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Any inherited method.

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Whether or not the inherited method is abstract like any abstract class it can also define new abstract

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and concrete methods.

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No if a subclass is non-abstract which means that it is a concrete subclass then it must always right

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.

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All of the unimplemented abstract methods.

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All of the unimplemented abstract methods so some of the abstract methods might have been implemented

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in one or more super classes.

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And the inheritance tree only them it does that or not implement it must be implemented in this class

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.

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Otherwise we do get compilation errors and that's not really a short demo of abstract process or an

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abstract methods for this item or a new folder.

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Abstract has been added in the directory structure.

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Com semantics clear up three new classes have been added here.

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One is abstract superclass abstract subclass an concrete subclass.

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So let's just go ahead and look at these classes.

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So this is abstract superclass.

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This is the most class and it is an abstract class so it is declared with the keyword abstract here

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so it is an abstract class.

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I need to close to abstract methods so both the methods have the keyword abstract.

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So next let's look at the subclass of this which is an abstract subclass So it extends abstract superclass

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and it is also abstract and it is overwriting only one method which is a best one matter.

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So if you're going to abstract superclass you have test too so it's overloading only one method with

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just one and it is simply printing out this text just one and you can ignore this notation.

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It just implies that it is already one of the superclass methods but Farnam you can ignore it because

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it's covered in a separate chapter and it is also declaring its own abstract method and your method

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called Destiny Dometic pesto which is declared here is not is not overridden in this in this particular

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class.

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Now let's look at concrete of class which is a subclass of abstract subclass.

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OK so this is a concrete subclass so you don't see the keyword abstract here and there are two methods

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to be implemented from the inheritance hierarchy which is a test to test 3.

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So test to was declared as an abstract method and the topmost class on pastry was declared as an abstract

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method an abstract subclass.

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So this particular class has to provide implementation implementations for all the unimplemented abstract

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methods so it provides the implementations here as do industry and here is the main method.

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Here we are just instantiating this class concrete subclass and we are invoking all the three methods

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.

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So let's just go ahead and compile and run this.

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So I'm in the abstract folder.

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Just compile this and let me just run it.

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Did you go at Brent's test run test do and best three.

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Now let's just also uncommon this class.

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It's just creating an instance of an abstract class which should give a compiler error because abstract

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classes cannot be instantiated.

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So let me just try to recompile this and as you can see it's is abstract superclasses abstract cannot

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be instantiated So that's a compilation of that and that we are getting.

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So that's the demo for abstract classes on.