Introduction to visitor pattern of Java design pattern

Visitor definition: the operation that acts on each object in an object group. It allows you to define new operations on these objects without changing the objects themselves.

In Java, the visitor pattern actually separates the elements in the collection structure and the behavior of operating on these elements.

Why do we use the visitor mode? Java collection (including vector and hashtable) is the technology we most often use, but the collection seems to be a large black dye vat. Once objects with various distinctive types are put in and taken out, these types disappear. Then we must use if to judge, such as: