Java Interview Guide : 200+ Interview Questions and Answers - Interface

The video tutorial covers the concept of interfaces in Java, explaining their purpose as a contract for classes to implement specific methods. It discusses how interfaces can define common actions across different classes, using examples like the map and collection interfaces in Java. The tutorial also explains how to define and implement interfaces, including changes introduced in Java 8, such as default method implementations. Advanced topics like extending interfaces and implementing multiple interfaces are also covered, providing a comprehensive understanding of interfaces in Java.

What is the primary purpose of an interface in Java?

• To store data

• To define a class

• To provide a default implementation

• To define a contract for classes

Which Java version introduced default method implementations in interfaces?

• Java 9

• Java 8

• Java 7

• Java 6

How do you define an interface in Java?

• Using the 'extends' keyword

• Using the 'interface' keyword

• Using the 'implements' keyword

• Using the 'class' keyword

What happens if a class does not implement all methods of an interface?

• The class will compile successfully

• The class will not compile

• The class will become abstract

• The class will throw a runtime error

What is a marker interface?

• An interface with default methods

• An interface with no methods

• An interface with a single method

• An interface that extends another interface

Can a class implement multiple interfaces in Java?

• No, a class can only extend multiple interfaces

• Yes, a class can implement multiple interfaces

• No, a class can only implement one interface

• Yes, but only if they are marker interfaces

Which of the following is true about variables in an interface?

• They can be private

• They are always public, static, and final

• They can be protected

• They are always instance variables