org.jplate.foundation.gof.visitor
Interface VisitableIfc<V extends VisitorIfc>

Type Parameters:

V - An implementation of Visitor who can perform operations on implementations of self.

All Known Subinterfaces:

BranchNodeIfc<BC,LC>, LeafNodeIfc<BC,LC>, NodeIfc<BC,LC>

All Known Implementing Classes:

AbstractNode, DefaultBranchNode, DefaultLeafNode

public interface VisitableIfc<V extends VisitorIfc>

This interface defines the API for a visitable object (namely those who can be operated upon by a VisitorIfc). Please refer to the definition of Visitor: "Represent an operation to be performed on the elements of an object structure. Visitor lets you define a new operation without changing the classes of the elements on which it operates," p331 Design Patterns - Elements of Reusable Object-Oriented Software.

The following example illustrates a trivial implementation of a person and related functionality:

• A visitor who defines opperations on a person:
  • PersonVisitorIfc: defines contract for visiting a person
  • ComputeTotalAge: can be used to keep a running total of ages of people.
  • ComputeTotalHeight: can be used to keep a running total of height of people.


• PersonCollection that supports iteration over a collection of PeopleIfc's applying a VisitorIfc to each one.

Code from the above description follows below:

public interface PersonVisitorIfc extends VisitorIfc
{
    public void visit ( Person person ) throws VisitException;
}

public class Person implements VisitableIfc <PersonVisitorIfc>
{
    int _age;
    int _height;

    public void accept ( PersonVisitorIfc pv ) throws VisitException
    {
        pv.visit ( this );
    }
}

public class ComputeTotalAge implements PersonVisitorIfc
{
    int _totalAge;

    public void visit ( Person person )
    {
        _totalAge += person._age;
    }
}

public class ComputeTotalHeight implements PersonVisitorIfc
{
    int _totalHeight;

    public void visit ( Person person )
    {
        _totalHeight += person._height;
    }
}

public class PersonCollection
{
    public static void processPeople
        ( Collection <Person> list, PersonVisitorIfc visitor )
            throws VisitException
    {
        for ( Person person : list )
        {
            person.accept ( visitor );
        }
    }
}
    

As can be seen, two operations are defined to operate upon a person - one that computes total height and another computing total age. Both operations are defined without affecting the concept of a person.

Modifications:
    $Date: 2008-12-02 12:32:45 -0500 (Tue, 02 Dec 2008) $
    $Revision: 479 $
    $Author: sfloess $
    $HeadURL: https://jplate.svn.sourceforge.net/svnroot/jplate/trunk/src/dev/java/org/jplate/foundation/gof/visitor/VisitableIfc.java $
    

Method Summary

void	accept(V visitor) Allows visitor to perform operations on self.

Method Detail

accept

void accept(V visitor)
            throws VisitException

Allows visitor to perform operations on self.

Parameters:

visitor - The object who will perform an operation on self.

Throws:

VisitException - If any problems arise performing an operation on self.