What is polymorphism in Java?

In Java, polymorphism refers to an object being able to take on multiple forms. This allows an object variable to reference different types of objects and call methods according to the actual type of the referenced object.

Polymorphism is an important feature of object-oriented programming that makes programs more flexible, scalable, and easier to maintain.

There are two ways to achieve polymorphism: inheritance and interfaces. Through inheritance, a subclass can inherit methods from a superclass and override them, thus achieving method polymorphism. Through interfaces, different classes can implement the same interface and provide their own implementation, thus achieving interface polymorphism.

For example, consider an Animal class with two subclasses, Dog and Cat. They all have a common method called speak(), but each subclass implements this method differently. Through polymorphism, an Animal class reference variable can be used to refer to Dog or Cat objects and call their speak() method. The compiler will determine which subclass method to call based on the actual type of the object. This way, a uniform operation can be performed on different types of objects without modifying the code.