During development or testing, create a class that implements the interface. This class can simulate the behavior of the class or service that actually implements the interface, so as to test and debug without relying on the actual component or service. In the Java programming language, an interface is an abstract type that defines a set of function methods (that is, method signatures) protocols. Stub is a commonly used software testing technology, which is used to simulate the actual components or services used in development and testing.