In Java, an abstract method is a method that is declared without an implementation (without braces, and followed by a semicolon) . It is used for creating blueprints for classes or interfaces, where methods are defined but dont provide the implementation. Abstract classes are classes that contain one or more abstract methods. An abstract class cannot be instantiated, but it can be subclassed. If a class includes abstract methods, then the class itself must be declared abstract. When an abstract class is subclassed, the subclass usually provides implementations for all of the abstract methods in its parent class. However, if it does not, then the subclass must also be declared abstract.

The purpose of abstract methods is to provide a way to define a method signature without providing the implementation. This allows subclasses to provide their own implementation of the method. Abstract methods are used to create blueprints for classes or interfaces, and they must be implemented by any concrete class that extends the abstract class. The purpose of abstract classes is to provide a common interface for a group of related classes. By using abstract classes, you can define a set of methods that must be implemented by any concrete class that extends the abstract class. This allows you to create a common interface for a group of related classes, which can simplify your code and make it easier to maintain.