中介者模式（Mediator），用一个中介对象来封装一系列的对象的交互。中介者使各对象不需要显式地相互引用，从而使其耦合松散，而且可以独立地改变它们之间的交互。

主方法

public class main {
    public static void main(String[] args) {
        UnitedNationsSecurityCouncil unsc = new UnitedNationsSecurityCouncil();

        USA c1 = new USA(unsc);
        Iraq c2 = new Iraq(unsc);

        unsc.setColleague1(c1);
        unsc.setColleague2(c2);

        c1.declare("不准研发核武器，否则要发动战争！");
        c2.declare("我们没有核武器，也不怕侵略");
        c1.declare("发动战争！");
    }
}

中介者抽象类

public abstract class UnitedNations {
    public abstract void declare(String message, Country colleague);
}

中介者实现类

public class UnitedNationsSecurityCouncil extends UnitedNations {
    private USA colleague1;
    private Iraq colleague2;

    public USA getColleague1() {
        return colleague1;
    }

    public void setColleague1(USA colleague1) {
        this.colleague1 = colleague1;
    }

    public Iraq getColleague2() {
        return colleague2;
    }

    public void setColleague2(Iraq colleague2) {
        this.colleague2 = colleague2;
    }

    public void declare(String message, Country colleague) {
        if(colleague == colleague1) {
            colleague2.getMessage(message);
        } else {
            colleague1.getMessage(message);
        }
    }
}

抽象成员类，构造函数中存在中介者

public abstract class Country {
    protected UnitedNations mediator;

    public Country(UnitedNations mediator) {
        this.mediator = mediator;
    }
}

成员类1

public class USA extends Country {
    public USA(UnitedNations mediator) {
        super(mediator);
    }

    public void declare(String message) {
        mediator.declare(message, this);
    }

    public void getMessage(String message) {
        System.out.println("美国获得对方消息：" + message);
    }
}

成员类2

public class Iraq extends Country {
    public Iraq(UnitedNations mediator) {
        super(mediator);
    }

    public void declare(String message) {
        mediator.declare(message, this);
    }

    public void getMessage(String message) {
        System.out.println("伊拉克获得对方信息：" + message);
    }
}