What are the characteristics of abstract classes in Java?

Characteristics of abstract classes in Java include:

1. Abstract classes cannot be instantiated and can only be used as parent classes to implement their subclasses through inheritance.
2. Abstract classes can have both abstract and non-abstract methods. Abstract methods are methods without a body, and subclasses must implement these abstract methods.
3. When a subclass inherits from an abstract class, it must implement all the abstract methods within the abstract class, unless the subclass is also an abstract class.
4. Abstract classes can include member variables, constructors, and regular methods.
5. Abstract classes cannot be declared as final classes.
6. Abstract classes can have static methods, static variables, and static code blocks.
7. Abstract classes can inherit from other classes or implement interfaces, but a class can only inherit from one abstract class.
8. Abstract classes can have constructors, but cannot be used to instantiate objects.