12/1/2023 0 Comments Java interface multiple extendsNote:-An interface contains variables and methods like a class but the methods in an interface are abstract by default unlike a class. This also does not cause any ambiguity because all methods declared in interfaces are implemented in class. ![]() In java, one class can implements two or more interfaces. ![]() The only way to implement multiple inheritance is to implement multiple interfaces in a class. The solution to the problem is interfaces. It creates problem during various operations like casting, constructor chaining etc and the above all reason is that there are very few scenarios on which we actually need multiple inheritance, so better to omit it for keeping the things simple and straightforward.Īlthough, multiple inheritance is no more a part of Java but still, there is a way we can implement the same along with resolving the ambiguity of the above-explained problem. ![]() Multiple inheritance is not supported by Java using classes, handling the complexity that causes due to multiple inheritance is very complex. Whether it should be Class B: foo() or Class C: foo(). In this image, Class A has a method named foo().Ĭlass B and Class C inherits from Class A and =overrides= the implementation of foo() in their own way.īut when Class D inherits from Class B and Class C, this leads to a confusion which =overridden= implementation to use in Class D. This is also called Diamond problem because structure on this inheritance scenario is similar to 4 edge diamond, see belowĮven if we remove the top head of diamond class A and allow multiple inheritances we will see this problem of ambiguity. So the 1st is ambiguity around Diamond problem, consider a class A has foo() method and then B and C derived from A and has there own foo() implementation and now class D derive from B and C using multiple inheritance and if we refer just foo() compiler will not be able to decide which foo() it should invoke. There are 2 reasons mentioned that will give you a idea why we don’t have multiple inheritance in java. One of the example of such problem is the diamond problem that occurs in multiple inheritance. Java doesn’t allow multiple inheritance to avoid the ambiguity caused by it. Why Java doesn’t support multiple inheritance?Ĭ++, Common lisp and few other languages supports multiple inheritance while java doesn’t support it. In simple words multiple inheritance in java means one class accessing the states and behavior of two or more than two interfaces simultaneously. If you extend M圜lass1 and M圜lass2, both classes have a foo (), and call super.foo () then the compiler is thrown by the Diamond Problem. As you can see the interface method to execute is defined and avoids the Diamond Problem entirely. Multiple inheritance in java means one class implementing two or more than two interfaces simultaneously. An example is: () where MyIFace is an interface. In simpler terms, multiple inheritance means a class extending more than one class. Object Oriented Programming provides a user the feature of multiple inheritance, wherein a class can inherit the properties of more than a single parent class. , X, and we want our new class A to inherit from all those classes.Enter fullscreen mode Exit fullscreen mode Initially we have the following external classes B, C, D. That may have sounded confusing, so let me explain better. You create an interface which specifies the public methods within the external classes which you would like to make use of, as well as methods within the new class you are creating, then you have your new class implement that interface. This makes class A what I would call a Fat class An interface can extend other interfaces, just as a class subclass or extend another class. Delegation allows a class A to pretend to be some other class B but any calls on A to some public method defined in B, actually delegates that call to an object of type B and the result is returned. This is a bit trickier, but it is doable by making use of delegation. class A įinally, there is also the case where you have just a bunch of classes to inherit from, but none of them are defined by you. What we can do with this is to turn A into an interface then, class C can implement A while extending B. Ok say you want a class C to extend classes, A and B, where B is a class defined somewhere else, but A is defined by us. ![]() In addition to the already accepted answer, I propose 3 more instances of this multiple inheritance problem and possible solutions to each. there exists a class A among the list of classes we would like to inherit from, where A is created by us. Well the answer depends on if we have at least one of the classes having been defined by us. we cannot change what one of those classes inherits from and therefore cannot make use of the accepted answer, what happens then? Most of the answers given seem to assume that all the classes we are looking to inherit from are defined by us.īut what if one of the classes is not defined by us, i.e.
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