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Java 8 Interview Questions and Answers

Question: Can you create your own functional interface?
Answer:
Yes, you can create your own functional interface. Java can implicitly identify functional interface but you can also annotate it with @FunctionalInterface.
Example:
Create interface named "Readable" as below:
public interface Readable {
    void read();
    default void readBook()
    {
        System.out.println("Reading the book.");
    }
}

Create main class named "MyFunctionalInteface":
public class MyFunctionalInteface {
    public static void main(String[] args)
    {
        MyFunctionalInteface myFuncInterface = new MyFunctionalInteface();
        myFuncInterface.readMyBook(() -> System.out.println("Reading my book"));
    }
    public void readMyBook(Readable p)
    {
        p.read();
    }
}

When you run above program, you will get below output:
Reading my book

As you can see, since Readable has only one abstract method called read(), we were able to call it using lambda expression.
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