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Why have interfaces in Java?

I was studying for my final and watching a video that said anything that an interface can do can also be done with abstraction…so why have interfaces? I hadn’t even thought about it before, but abstract classes and interfaces do seem really similar so can anyone explain why we need both or how to know which one to use?

10/27/2021 11:42:12 PM

Jocelyn

3 Answers

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A class can inherit only one abstract class, but it can inherit unlimited number of interfaces. Sometimes you cannot extend an abstract class for some reason. This is when interfaces come in handy. That's why we need both.

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an interface is a little more abstract than an abstract class which eg. can use non-final member fields (variables). So in order abstract -> concrete is .interface used first for general list of methods and .abstract class for partially implemented approximation for programers comfort https://code.sololearn.com/cBZ58X6SN53O/?ref=app

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Since java does not support multiple classes of inheritance to accomplish this Java introduced a concept called interface An interface can extends any no of interfaces A class can imolements any no of interfaces Interfaces that are not having any kind of methods are called markable market interface or tagging interface Ex Remote Interfaces having only one method called as functional interface Ex Runnable Every variable declared in interfaces are by default final Every method is by default public scope Interface is used if every feature is changing for each object Subclass have to implement abstract methods defined in interface If subclass is not implementing all abstract methods the subclass should be abstract We can to create another subclass to implement remaining abstract methods Ex interface Welcome { void test(); }