import static java.lang.System.*;
import java.util.*;

/**********************************************************************
 * This class show how to implement bidirectional many-to-one
 * associations between classes C and D.
 */
public class Association
{

    /******************************************************************
     * Class C is the many side (maps to one d).
     */
    public static class C {

        private D d;

        public D getD ()
        {
            return d;
        } // getD

        public void setD (D d2)
        {
            out.println ("setD ( " + d2 + " )");
            if (d != d2) {
                D d0 = d;
                d = d2;
                if (d0 != null) d0.removeC (this);
                if (d2 != null) d2.addC (this);
            } // if
        } // setD

    } // C class

    /******************************************************************
     * Class D is the one side (maps to many c's).
     */
    public static class D {

        private Set<C> cs = new HashSet<C> ();

        public void printSet ()
        {
            for (C c : cs) {
                out.println ("c <- d = " + c + " , " + this);
            } // for
        } // printSet

        public void addC (C c)
        {
            out.println ("addD ( " + c + " )");
            cs.add (c);
            c.setD (this);
        } // addC

        public void removeC (C c)
        {
            out.println ("removeC ( " + c + " )");
            cs.remove (c);
            c.setD (null);
        } // removeC

    } // D class

    /******************************************************************
     * Main method to test the association.
     */
    public static void main (String [] args)
    {
        C c_1 = new C ();
        D d_1 = new D ();

        out.println ("------------------------");
        out.println (" c_1 = " + c_1);
        out.println (" d_1 = " + d_1);
        out.println ("------------------------");
        c_1.setD (d_1);
        out.println ( "c -> d = " + c_1 + " , " + c_1.getD ());
        out.println ("------------------------");
        d_1.printSet ();
        out.println ("------------------------");

        D d_2 = new D ();

        out.println ("------------------------");
        out.println (" d_2 = " + d_2);
        out.println ("------------------------");
        c_1.setD (d_2);
        out.println ( "c -> d = " + c_1 + " , " + c_1.getD ());
        out.println ("------------------------");
        d_2.printSet ();
        out.println ("------------------------");

        C c_2 = new C ();

        out.println ("------------------------");
        out.println (" c_2 = " + c_2);
        out.println ("------------------------");
        c_2.setD (d_2);
        out.println ( "c -> d = " + c_2 + " , " + c_2.getD ());
        out.println ("------------------------");
        d_2.printSet ();
        out.println ("------------------------");

    } // main

} // Association