Java interface multiple extends10/13/2023 ![]() To simplify, let us consider one of the above cases, where we wanted to have a new “role”, which we call “ADP” and this role has the responsibilities of Architect, Developer and Project Manager combined. Project Manager, Architect and Developer can wear the cap of Tester anytime during the project lifecycle.A senior technical resource can perform the roles of Architect and Developer.A senior technical-management resource can perform the roles of Project Manager, Architect and Developer.For example, given the circumstances and the skill sets: Now, in real world, this happens quite often and specially in a Software Consulting Firm that a person can “perform” the roles of more than one types. All the five? yes Employee is inheriting from Object class following the rules of Java Language Specification that if a class is not inherited from any other class then by default it will be inherited from the Object class. all the five classes are inheriting a single Parent Class. This is the simple example of (Single) Inheritance in Java i.e. Thinking in Object Oriented, you can easily depict that Employee is the Base or Parent Class and Developer, Tester, Architect and ProjectManager are Derived or Child Classes. ![]() All of these are Employee(s) of the Software Consulting Form i.e. To simplify things a bit, assume there are 4 roles Developer, Tester, Architect and Project Manager. For a refresher on these topics, there’s a very informative post on Artima Developer where Erich Gamma, co-author of the landmark book, Design Patterns, talks with Bill Venners about two design principles: program to an interface, not an implementation, and favor object composition over class inheritance.įor our example, consider different type of Employment Roles available in a typical Software Consulting Firm. ![]() Note:-An interface contains variables and methods like a class but the methods in an interface are abstract by default unlike a class.In this post I will demonstrate the use of ‘Program To Interface’ Design Principle and Object Composition, to emulate Multiple Inheritance in Java. 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. ![]() Multiple inheritance in java means one class implementing two or more than two interfaces simultaneously. 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. Enter fullscreen mode Exit fullscreen mode
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