Interface

1. What is an interface in Java?
Ans: An interface in Java is a mechanism that is used to achieve complete abstraction. It is basically a kind of
class that contains only constants and abstract methods.

2. Which modifiers are allowed for methods in an Interface?Explain with an example
Ans: Only abstract and public modifiers are allowed for methods in interfaces.

3. What is the use of interface in Java?
Ans: There are many reasons to use interfaces in java. They are as follows:
a. An interface is used to achieve full abstraction.
b. Using interfaces is the best way to expose our project’s API to some other project.
c. Programmers use interfaces to customise features of software differently for different objects.
d. By using interface, we can achieve the functionality of multiple inheritance.


4. What is the difference between abstract class and interface in Java?
In Java, both abstract classes and interfaces are used to define common behavior that can be inherited by subclasses. However, there are several differences between them:

Method implementation: An abstract class can have both abstract and non-abstract methods, whereas an interface can only have abstract methods (default methods and static methods were introduced in Java 8 and Java 9, respectively). Abstract methods are defined without an implementation, while non-abstract methods have an implementation.

Multiple inheritance: A class can extend only one abstract class, but it can implement multiple interfaces. This means that interfaces can provide a way to achieve multiple inheritance in Java.

Accessibility: Methods and variables in an interface are always public, whereas an abstract class can have any accessibility level. This means that interfaces can provide a more strict way to enforce behavior across different classes.

Constructor: An abstract class can have a constructor, whereas an interface cannot have a constructor.

Purpose: Abstract classes are typically used to represent a general type of object, while interfaces are typically used to define behavior that can be implemented by multiple classes.