11 - Interfaces
In Java, an interface is a reference type that is similar to a class. It is a collection of abstract methods. When a class implements an interface, it inherits the abstract methods defined in that interface, and the implementing class must provide concrete implementations for those methods. In addition to abstract methods, interfaces can also include constants and default methods.
Interfaces provide a way to achieve abstraction, multiple inheritance, and the definition of a contract for implementing classes. They are commonly used in Java to define APIs, ensuring a consistent set of methods and functionality across different classes.