Thursday, 20 January 2005 21:38

Define an object that encapsulates how a set of objects interact. Mediator promotes loose coupling by keeping objects from referring to each other explicitly, and it lets you vary their interaction independently.

Source code

/**
 * Each colleague knows its Mediator object. Communicates with its mediator
 * whenever it would have otherwise communicated with another colleague.
 * 
 * @role __Colleague
 */
public abstract class Colleague {
        /** my mediator */
        private Mediator mediator;        /** Create colleague which knows about supplied mediator */
        protected Colleague(Mediator mediator) {
                this.mediator = mediator;        }

        /** @return mediator this colleague knows about */
        public Mediator getMediator() {
                return mediator;        }

}

/** Concrete Colleague */
public class ConcreteColleagueA extends Colleague {
        public ConcreteColleagueA(Mediator mediator) {
                super(mediator);        }

        public void sampleOperation() {
                // some state changes occur,
                // notify mediator about them
                getMediator().changed(this);        }

}

/** Concrete Colleague */
public class ConcreteColleagueB extends Colleague {
        public ConcreteColleagueB(Mediator mediator) {
                super(mediator);        }

        public void sampleOperation() {
                // some state changes occur,
                // notify mediator about them
                getMediator().changed(this);        }

}

/**
 * Implements cooperative behavior by coordinating Colleague objects. Knows and
 * maintains its colleagues.
 */
public class ConcreteMediator implements Mediator {
        /** reference to concrete colleague */
        private ConcreteColleagueA aConcreteColleagueA;        /** reference to concrete colleague */
        private ConcreteColleagueB aConcreteColleagueB;        public void changed(Colleague colleague) {
                // handle changes of particular colleague
        }

        public void setConcreteColleagueA(ConcreteColleagueA colleague) {
                aConcreteColleagueA = colleague;        }

        public void setConcreteColleagueB(ConcreteColleagueB colleague) {
                aConcreteColleagueB = colleague;        }

}

/**
 * Defines an interface for communicating with Colleague objects.
 * 
 * @role __Mediator
 */
public interface Mediator {
        /** Colleagues calls this method to notify Mediator that something changed */
        void changed(Colleague colleague);}

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