What is an abstract class in Java?

An abstract class is a class declared with the abstract keyword that cannot be instantiated directly — you must create a concrete subclass that provides implementations for all abstract methods. Abstract classes can have a mix of abstract methods (declared without a body) and concrete methods (with a body). They can also have constructors, instance fields, and static members. Use abstract classes to define a common template for a family of related classes, providing shared implementation while forcing subclasses to implement specific behaviors. Example: an abstract Shape class with an abstract area() method, implemented differently by Circle, Rectangle, etc.