Object Oriented Programming Questions Long
An abstract class and an interface are both important concepts in object-oriented programming, but they have some key differences.
1. Definition: An abstract class is a class that cannot be instantiated and is meant to be inherited by other classes. It can contain both abstract and non-abstract methods. On the other hand, an interface is a blueprint of a class that defines a set of methods that a class must implement. It only contains abstract methods and constants.
2. Inheritance: An abstract class can be extended by other classes using the "extends" keyword, and a class can only extend one abstract class. This allows the subclass to inherit the properties and methods of the abstract class. On the other hand, a class can implement multiple interfaces using the "implements" keyword. This allows the class to provide implementations for all the methods defined in the interface.
3. Method Implementation: An abstract class can have both abstract and non-abstract methods. Abstract methods are declared without any implementation and must be overridden by the subclass. Non-abstract methods have a default implementation in the abstract class but can also be overridden by the subclass if needed. In contrast, an interface can only have abstract methods, which means they are declared without any implementation. The implementing class must provide the implementation for all the methods defined in the interface.
4. Access Modifiers: In an abstract class, methods and variables can have different access modifiers like public, private, protected, etc. This allows for more flexibility in controlling the visibility of members. In an interface, all methods are implicitly public and all variables are implicitly public, static, and final. Therefore, there is no need to specify access modifiers explicitly.
5. Object Type: An abstract class can be used to create objects, but it cannot be instantiated itself. It serves as a base for creating subclasses. On the other hand, an interface cannot be used to create objects directly. It is used to define a contract that a class must adhere to.
6. Multiple Inheritance: As mentioned earlier, a class can only extend one abstract class, but it can implement multiple interfaces. This is because Java supports multiple interface inheritance but not multiple class inheritance. This allows for more flexibility in reusing code and implementing different behaviors.
In summary, the main differences between an abstract class and an interface are related to their purpose, inheritance, method implementation, access modifiers, object type, and multiple inheritance. Understanding these differences is crucial for designing and implementing effective object-oriented solutions.