Yes, an abstract class in Java can extend another abstract class. This is a common and valid practice in object-oriented design, particularly when dealing with hierarchies of related concepts where each level introduces more specific abstract behaviors or implements some common functionality.

When an abstract class extends another abstract class:

• Inheritance of Members:

  It inherits all the members (fields, concrete methods, and abstract methods) from its parent abstract class.

• Abstract Method Implementation (Optional):

  The child abstract class is not required to implement the abstract methods inherited from its parent. It can choose to leave them abstract, forcing subsequent concrete subclasses to provide the implementation.

• Adding New Abstract Methods:

  The child abstract class can declare new abstract methods specific to its level of abstraction.

• Providing Concrete Implementations:

  It can also provide concrete implementations for some or all of the inherited abstract methods, or for its own newly declared abstract methods.

This allows for a gradual refinement of abstract behavior down the inheritance hierarchy, with concrete classes at the bottom of the hierarchy ultimately providing the full implementation for all inherited abstract methods.