Visitor Pattern

Visitor is one of the more specialized behavioral patterns. It is most useful when:

• the object structure is relatively stable
• many different operations must be applied to it
• you want to keep those operations out of the element classes

It is commonly discussed with ASTs, document models, and other structured object graphs. It is usually a poor fit when element types change frequently.

In this section

• Implementing Visitor in Java
  Implement Visitor in Java when the object structure is stable and the system needs multiple separate operations over it.
• Double Dispatch in the Visitor Pattern
  Understand Java Visitor double dispatch so the chosen visit method depends on both the element type and the visitor type.
• Extensibility with Visitors
  Understand the real extensibility trade-off in Java Visitor: new operations are easy, new element types are expensive.
• Visitor vs. Iterator Pattern
  Compare Visitor and Iterator in Java so traversal and operation-separation concerns are not treated as the same design move.
• Visitor Pattern Use Cases and Examples in Java
  See where Visitor genuinely helps in Java systems, especially with ASTs, document trees, rule structures, and stable object models needing many operations.