What are the purposes and characteristics of Java abstract classes?

An abstract class is a type of class that cannot be instantiated and can only be inherited. Its purpose is to define common properties and methods for subclasses. The role and characteristics of an abstract class are as follows:

1. Abstract classes can have both abstract methods, which must be implemented by subclasses, and non-abstract methods, which subclasses can choose to override.
2. Abstract classes can define common attributes and methods, preventing subclasses from redefining the same attributes and methods and improving code reusability.
3. Abstract classes can serve as a standard, requiring subclasses to implement specified methods to ensure they have specific functionality.
4. Abstract classes cannot be instantiated and can only be used for inheritance. Subclasses must implement all abstract methods in the abstract class in order to be instantiated.

In conclusion, abstract classes offer a template or guideline for defining common behaviors and attributes for subclasses, while also requiring subclasses to implement abstract methods to ensure code consistency and reliability.