Design Patterns | Visitor

---

1. References
2. Example
   • The Visitor
   • The Concrete Visitor
   • The Element
   • The Concrete Element (1)
   • The Concrete Element (2)
   • A simple class to test the Visitor design pattern

---

1. References
   • Definition: (source: http://en.wikipedia.org/wiki/Visitor_pattern)
     
     The visitor design pattern is a way of separating an algorithm from an object structure on which it operates.
     A practical result of this separation is the ability to add new operations to existing object structures without modifying those structures.
     
     
   • Class diagram: (source: http://en.wikipedia.org/wiki/Visitor_pattern)
     
     
2. Example
   • The Visitor:
     
     public interface Visitor { void visit(final Debit debit); void visit(final Credit credit); }
     
   • The Concrete Visitor:
     
     public class VisitorImpl implements Visitor { public void visit(final Debit debit) { System.out.println("Visit Debit ..."); } public void visit(final Credit credit) { System.out.println("Visit Credit ..."); } }
     
   • The Element:
     
     public interface Payment { void accept(final Visitor visitor); }
     
   • The Concrete Element (1):
     
     public class Debit implements Payment { public void accept(final Visitor visitor) { visitor.visit(this); } }
     
   • The Concrete Element (2):
     
     public class Credit implements Payment { public void accept(final Visitor visitor) { visitor.visit(this); } }
     
   • A simple class to test the Visitor design pattern:
     
     public class VisitorPatternTest { public static void main(String[] args) { final Payment debit = new Debit(); final Payment credit = new Credit(); final Visitor visitor1 = new VisitorImpl(); debit.accept(visitor1); credit.accept(visitor1); } }