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Hi there.

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So this chapter is all about inheritance and we have learned a great deal about it.

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We know that with inheritance we not only inherit functionality but also extend on all the existing

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behavior defined in the super to us non-Nazi how we can do the opposite which is to prevent inheritance

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.

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So there can be instances where you want to prevent inheritance that is you want to a class to be the

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final version.

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So let's see why you would want to do this on also how it can be done.

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One reason why you want to prevent inheritance is that you do not want your methods to be overridden

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.

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That's because you want them to work in the exact same way as you have implemented them.

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However sometimes it's not just about method or writing but you do not want any subprocess to be created

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as they may affect the semantics of your class.

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In other words you do not want the invariants that are defined by your class to be compromised by subprocess

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.

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For example we know string classes immutable and the designers did not want subclasses of string to

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be created as they could compromise this immutable behavior.

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So the String class and just this by preventing inheritance altogether in fact item 15 in Effective

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Java recommends minimizing notability off classes as much as possible on one of the rules and doing

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it is to prevent inheritance.

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Item 15 is pretty important on its own point.

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I tried to include it as a separate lesson.

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Now there are two ways to prevent inheritance.

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One is by marking the classes final while the other is by using a private constructor.

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Let's look at both of them.

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We already look good using the final keyword with both variables and methods.

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We said that if Final is used with a variable then its value can never be changed.

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If final is used with a specific method then that method can never be overridden.

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Similarly a final key word is used in class declaration.

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Then the class can never be extended.

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It also means that none of its methods can ever be overridden.

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So essentially final implies that something is final or whatever however final process intangible.

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So it is not expendable but it is still intangible.

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And one good example is the string.

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If you look at it source code you will also see that it's class declaration includes the final keyword

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.

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One reason why you want to pay for using the word final as opposed to the second approach that prevents

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inheritance is because it is instantiation which helps in defining state as well as defining instance

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methods which can work on that state.

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And that's what is happening with the string class where it is initialized with some text and then there

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are instance methods that can be used to manipulate that text.

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Now if you do not want your class to be extendable under at the same time to be not intangible then

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you would have to go with the second approach which is to use or NEAP private constructor.

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If you recall we discussed this while covering static maggot's he specifically discussed an effective

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diadem and said that if the class is a utility class like the map class where all the methods are static

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then you can make the class non-intentional by marking its concept private.

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We said that the benefit of doing it was that it would save us heaps because as we can no longer instantiate

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the class.

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And in fact it is meaningless to create such an instance when all its methods are static but we don't

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know that the second advantage is that the class is not extendable.

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There is also a technical reason on why it cannot be extended.

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And can you guess the reason and the reason is constipate is more pirate that is a private access where

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meets the constructor private to the class and so cannot be invoked from supperless.

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And if it cannot be in principle it means constructor chaining is not possible.

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So the subclass cannot be created.

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So to summarize if your class should not be extended but have stayed involved with methods depending

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on it then go for the final keyword example in string class as methods in the string class work on the

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strings input data.

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But if you are dealing with something like a utility class which includes only static methods then you

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can make the constructors blame it on it would present instantiation as an add on the class is no longer

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extendable.

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So if you want a utility class that only static methods that should not be extended then you can go

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for this private constructor option.

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But if you want your utility class to be extended then of course do not include the private constructor

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unload the class include only static markets and with that subclasses can add new methods.

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So that's a bug why and how you can prevent inheritance.

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Typically most inheritance hierarchies are wide but not deep.

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Usually they are one or two levels deep but there is no hard limit on it and just go ahead.

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On Monday user classes final on see how we get a compilation error on the staff plus as it extends the

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user class.

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Thank you