What is the Difference Between Abstract Class and Concrete Class?

The main difference between an abstract class and a concrete class in Java is that an abstract class can have abstract methods, while a concrete class cannot. Here are some key differences between the two:

• Abstract Class:
• Declared using the abstract keyword.
• Can have both abstract and concrete methods.
• Cannot be directly instantiated using the new keyword.
• Must be inherited by a concrete subclass or implemented by an interface.
• Cannot implement an interface alone; a child class is needed for instantiation.
• Cannot be declared as final.
• Concrete Class:
• Not declared using the abstract keyword.
• Can only have concrete methods; even a single abstract method makes the class abstract.
• Can be directly instantiated using the new keyword.
• Implements all the abstract methods of its parent abstract class.
• Can implement interfaces.
• Can be declared as final.

In summary, an abstract class is a blueprint for concrete classes, containing abstract methods that must be implemented by subclasses. A concrete class, on the other hand, is a fully implemented class that implements all the methods, including those inherited from abstract classes or interfaces.

Comparative Table: Abstract Class vs Concrete Class

Here is a table comparing the differences between abstract classes and concrete classes:

In summary, abstract classes can contain abstract methods and can inherit from other classes or implement interfaces, but they cannot be directly instantiated. Concrete classes, on the other hand, do not contain abstract methods and can be directly instantiated. They can also be declared as final and implement interfaces directly.