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21.Difference between abstract class and interface Abstract class and interface both are used to achieve abstraction where we can declare the abstract methods. Abstract class and interface both can't be instantiated. But there are many differences between abstract class and interface that are given below. Abstract class Interface 1) Abstract class can  have abstract and non-abstract  methods. Interface can have  only abstract  methods. Since Java 8, it can have  default and static methods  also. 2) Abstract class  doesn't support multiple inheritance . Interface  supports multiple inheritance . 3) Abstract class  can have final, non-final, static and non-static variables . Interface has  only static and final variables . 4) Abstract class  can provide the implementation of interface . Interface  can't provide the implementation of abstract class . 5) The  abstract keyword  is used to declare abstract class. The  interface keyword  is used to declare interface. 6) An  abstra

Polymorphism in Java  is a concept by which we can perform a  single action in different ways . Polymorphism is derived from 2 Greek words: poly and morphs. The word "poly" means many and "morphs" means forms. So polymorphism means many forms. There are two types of polymorphism in Java: compile-time polymorphism and runtime polymorphism. We can perform polymorphism in java by method overloading and method overriding. If you overload a static method in Java, it is the example of compile time polymorphism. Here, we will focus on runtime polymorphism in java. next → ← prev Polymorphism in Java Polymorphism in Java  is a concept by which we can perform a  single action in different ways . Polymorphism is derived from 2 Greek words: poly and morphs. The word "poly" means many and "morphs" means forms. So polymorphism means many forms. There are two types of polymorphism in Java: compile-time polymorphism and runtime polymorphism.