只有一个仲裁者

Mediator 模式

组员向仲裁者报告，仲裁者向组员下达指示，组员之间不在相互询问和相互指示。

要调整多个对象之间的关系时，就需要用到 Mediator 模式。将逻辑处理交给仲裁者执行。

示例程序

Mediator.java

package mediator;

public interface Mediator {
    public abstract void createColleague();
    public abstract void colleagueChanged();
}

Colleague.java

package mediator;

public interface Colleague {
    public abstract void setMediator(Mediator mediator);
    public abstract void setColleagueEnabled(boolean enabled);
}

ColleagueButton.java

package mediator;

import java.awt.*;

public class ColleagueButton extends Button implements Colleague {
    private Mediator mediator;
    public ColleagueButton(String caption) {
        super(caption);
    }
    public void setMediator(Mediator mediator) {
        this.mediator = mediator;
    }
    public void setColleagueEnabled(boolean enabled) {
        setEnabled(enabled);
    }
}

ColleagueTextField.java

package mediator;

import java.awt.*;
import java.awt.event.TextEvent;
import java.awt.event.TextListener;

public class ColleagueTextField extends TextField implements TextListener, Colleague {
    private Mediator mediator;
    public ColleagueTextField(String text, int columns) {
        super(text, columns);
    }
    public void setMediator(Mediator mediator) {
        this.mediator = mediator;
    }
    public void setColleagueEnabled(boolean enabled) {
        setEnabled(enabled);
        setBackground(enabled ? Color.WHITE : Color.lightGray);
    }
    public void textValueChanged(TextEvent e) {
        mediator.colleagueChanged();
    }
}

ColleagueCheckbox.java

package mediator;

import java.awt.*;
import java.awt.event.ItemEvent;
import java.awt.event.ItemListener;

public class ColleagueCheckbox extends Checkbox implements ItemListener, Colleague {
    private Mediator mediator;
    public ColleagueCheckbox(String caption, CheckboxGroup group, boolean state) {
        super(caption, group, state);
    }
    public void setMediator(Mediator mediator) {
        this.mediator = mediator;
    }
    public void setColleagueEnabled(boolean enabled) {
        setEnabled(enabled);
        setBackground(enabled ? Color.WHITE : Color.lightGray);
    }
    public void itemStateChanged(ItemEvent e) {
        mediator.colleagueChanged();
    }
}

LoginFrame.java

package mediator;

import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

public class LoginFrame extends Frame implements ActionListener, Mediator {
    private ColleagueCheckbox checkGuest;
    private ColleagueCheckbox checkLogin;
    private ColleagueTextField textUser;
    private ColleagueTextField textPass;
    private ColleagueButton buttonOk;
    private ColleagueButton buttonCancel;

    // 构造函数
    // 生成并配置各个Colleague后，显示对话框
    public LoginFrame(String title) {
        super(title);
        setBackground(Color.lightGray);
        setLayout(new GridLayout(4, 2));
        createColleague();
        add(checkGuest);
        add(checkLogin);
        add(new Label("Username:"));
        add(textUser);
        add(new Label("Password:"));
        add(textPass);
        add(buttonOk);
        add(buttonCancel);
        colleagueChanged();
        pack();
        show();
    }

    public void createColleague() {
        CheckboxGroup g = new CheckboxGroup();
        checkGuest = new ColleagueCheckbox("Guest", g, true);
        checkLogin = new ColleagueCheckbox("Login", g, false);
        textUser = new ColleagueTextField("", 10);
        textPass = new ColleagueTextField("", 10);
        textPass.setEchoChar('*');
        buttonOk = new ColleagueButton("OK");
        buttonCancel = new ColleagueButton("Cancel");
        checkGuest.setMediator(this);
        checkLogin.setMediator(this);
        textUser.setMediator(this);
        textPass.setMediator(this);
        buttonOk.setMediator(this);
        buttonCancel.setMediator(this);
        checkGuest.addItemListener(checkGuest);
        checkLogin.addItemListener(checkLogin);
        textUser.addTextListener(textUser);
        textPass.addTextListener(textPass);
        buttonOk.addActionListener(this);
        buttonCancel.addActionListener(this);
    }

    public void colleagueChanged() {
        if (checkGuest.getState()) {
            textUser.setColleagueEnabled(false);
            textPass.setColleagueEnabled(false);
            buttonOk.setColleagueEnabled(true);
        } else {
            textUser.setColleagueEnabled(true);
            userpassChanged();
        }
    }

    private void userpassChanged() {
        if (textUser.getText().length() > 0) {
            textPass.setColleagueEnabled(true);
            if (textPass.getText().length() > 0) {
                buttonOk.setColleagueEnabled(true);
            } else {
                buttonOk.setColleagueEnabled(false);
            }
        } else {
            textPass.setColleagueEnabled(false);
            buttonOk.setColleagueEnabled(false);
        }
    }

    public void actionPerformed(ActionEvent e) {
        System.out.println(e.toString());
        System.exit(0);
    }
}

Main.java

package mediator;

public class Main {
    static public void main(String args[]) {
        new LoginFrame("Mediator Sample");
    }
}

Mediator 模式中的角色

1. Mediator(仲裁者、中介者)

   Mediator 角色负责定义与 Colleague 角色进行通信和做出决定的接口。

2. ConcreteMediator(具体的仲裁者、中介者)

   ConcreteMediator 角色负责实现 Mediator 角色的接口，负责实际做出决定。

3. Colleague(同事)

   Colleague 角色负责定义与 Mediator 角色进行通信的接口。

4. ConcreteColleague(具体的同事)

   ConcreteColleague 角色负责实现 Colleague 角色的接口。

拓展思路

一、Bug容易定位，因为没有别的控制控件做逻辑控制处理。

二、ConcreteColleague 角色可以复用，ConcreteMediator 角色难以复用。