Interview questions on java 8 Functional Interface for experienced

Part 2

Interview questions on Java 8 Functional Interface for  experienced covered in this post: 

    What is functional Interface?

-          An Interface with only one abstract method is called a functional interface.

-          @FunctionalInterface annotation can be used to indicate.

-          If an interface has more than one abstract method then it is not a functional interface it is a regular interface.

-          Functional interface can have multiple default and static methods but only one abstract method.

-          Lambda expression can work with a functional interface only. Lambda expression cannot work with a regular interface that has multiple abstract methods.

-          Please refer to the below example for the functional interface.

package simplifiedjava.crackedInterview.java8;  @FunctionalInterface public interface FunctionalInterfaceDemo {       public void add(); }

 

    Can you list out some functional interface used in java 6?

-          FunctionalInterface must have only one abstract method.

-          We have used 4 functional interfaces.

1.       Runnable: Runnable interface has run() method.

2.       Callable: Callable interface has call() method.

3.       ActionListener: ActionListener has actionPerformed() method.

4.       Comparable: Comparable has compareTo() method.

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    Can I have multiple abstract methods in functional interface?

-          No, we cannot have multiple abstract methods in the functional interface.

-          If you declare multiple abstract methods inside an interface and an interface is not annotated with @FunctionalInterface then it will become a regular interface.

-          If you declare multiple abstract methods inside an interface and an interface is annotated with @FunctionalInterface then it will give a compile-time error.

-          If you declare only one abstract methods and multiple default and static method but not annotated with @FunctionalInterface then it is also functional interface.

 

    Which annotation can be used to make functional interface?

-          @FunctionalInterface Annotation can be used to make any Interface as functional interface.

-          Please refer to the below example.

package simplifiedjava.crackedInterview.java8;  @FunctionalInterface public interface FunctionalInterfaceDemo {       public void add(); }

 

    What will happen if I declared multiple abstract methods in one interface?

-          If you declare multiple abstract methods inside interface and interface is annotated with @FunctionalInterface then it will give a compile-time error.

-          If you declare multiple abstract methods inside interface and interface is not annotated with @FunctionalInterface then it will become a regular interface.

• Java interview questions and answers all MNC - Click here

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• Core java interview questions and Answers for 5 - 7 Years exp - Click here

• Basic Java Interview Questions and Answers - Click here

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• Interview questions on multithreading in java for experienced - Click here

• Interview questions on serialization in java for experienced - Click here

• Interview questions on inner class in java for experienced - Click here

• Interview questions on Collections in java for experienced - Click here

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