How a class implements an interface in Java.

Explain with an example how a class implements an interface.

First ,the interface is to be defined. Defining an interface is placing the method signatures. Then these methods are to be overridden in the class that implements the interface.

interface QuestionAnswer
   String answerForQuestion(String qtn);
class AnswerForQuestion implements QuestionAnswer
   String answerForQuestion(String qtn)
       System.out.println(“The answer is “ + qtn);
Create an object of the class AnswerForQuestion and invoke the answerForQuestion() method.
AnswerForQuestion afq = newAnswerForQuestion();
afq.answerForQuestion(“Java is a programming language”);

When a class implements an interface, it has to implement the methods defined inside that interface.

This is enforced at build time by the compiler.
interface interfaceA
   void methodA(int x);

class classA implements interfaceA
   // implementation for methodA and the rest of the class code if any.
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