The visitor design pattern addresses the challenge of adding new behavior to similar classes without modifying them, by allowing new algorithms to be written in a separate visitor class. This pattern requires creating a visitor interface and concrete visitors, enabling elements to accept visitors and execute their associated behavior. While it adheres to principles like open/closed and single responsibility, it can lead to maintenance challenges if the class hierarchy changes.

1. VISITOR DESIGN PATTERN
MHD SALEM KABBANI

2. PROBLEM
• When we have similar classes and we want to add new
behavior to them.
• Each one of those classes should performs the new behavior in
different way.
• This operation forces us to modify all those class.

3. VISITOR PATTERN
• Visitor pattern is one of the behavioral design patterns.
• It allows you to add new behavior to an existed class without
modifying it.
• New behavior (algorithm) is written in the visitor class which
allows to separate the algorithm from object structure.

4. SOLUTION
• We create visitor interface which has visit method for each type
of our concrete elements.
• Concrete visitor implements visitor and its visit methods.
• Each concrete element implements element interface which
contains accept method.
• Accept method takes visitor interface as a parameter and
returns visitor’s visit with current object.

5. UML

6. IMPLEMENTATION

7. IMPLEMENTATION

8. IMPLEMENTATION
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9. PROS. VS CONS.
• Needs to update all visitors
each time a class gets added
to or removed from the
element hierarchy.
• Visitors might lack the
necessary access to the
private fields and methods of
the elements that they’re
supposed to work with.
• Open/Closed Principle: add a
new behavior that works with
objects of different classes
without changing these
classes.
• Single Responsibility
Principle: move multiple
versions of the same behavior
into the same class.