设计模式-状态模式

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状态模式

定义

在状态模式（State Pattern）中，类的行为是基于它的状态改变的。

在状态模式中，我们创建表示各种状态的对象和一个行为随着状态对象改变而改变的 对象。

类图

状态模式类图

State（状态）

表示了状态，定义了根据不同状态进行不同处理的接口。该接口是那些处理内容依赖于状态的方法的集合。

ConcreteState

表示各个具体状态，它实现了State接口

Context（状况、前后关系、上下文）

持有表示当前状态的ConcreteState对象。此外，它还定义了供外部滴啊用着使用State模式的接口。

示例

类图

状态模式示例类图

Context

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public interface Context {

    public abstract void setClock(int hour);                
    public abstract void changeState(State state);          
    public abstract void callSecurityCenter(String msg);    
    public abstract void recordLog(String msg);             
}

DayState

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public class DayState implements State {
    private static DayState singleton = new DayState();
    private DayState() {                                
    }
    public static State getInstance() {                
        return singleton;
    }
    public void doClock(Context context, int hour) {    
        if (hour < 9 || 17 <= hour) {
            context.changeState(NightState.getInstance());
        }
    }
    public void doUse(Context context) {                
        context.recordLog("4");
    }
    public void doAlarm(Context context) {             
        context.callSecurityCenter("3");
    }
    public void doPhone(Context context) {              
        context.callSecurityCenter("2");
    }
    public String toString() {                          
        return "1";
    }
}

NightState

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public class NightState implements State {
    private static NightState singleton = new NightState();
    private NightState() {                              
    }
    public static State getInstance() {                 
        return singleton;
    }
    public void doClock(Context context, int hour) {    
        if (9 <= hour && hour < 17) {
            context.changeState(DayState.getInstance());
        }
    }
    public void doUse(Context context) {                
        context.callSecurityCenter("1");
    }
    public void doAlarm(Context context) {              
        context.callSecurityCenter("1");
    }
    public void doPhone(Context context) {              
        context.recordLog("1");
    }
    public String toString() {                          
        return "2";
    }
}

SafeFrame

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public class SafeFrame extends Frame implements ActionListener, Context {
    private TextField textClock = new TextField(60);        
    private TextArea textScreen = new TextArea(10, 60);     
    private Button buttonUse = new Button("123");      
    private Button buttonAlarm = new Button("456");    
    private Button buttonPhone = new Button("789");    
    private Button buttonExit = new Button("101112");         

    private State state = DayState.getInstance();           

    public SafeFrame(String title) {
        super(title);
        setBackground(Color.lightGray);
        setLayout(new BorderLayout());
        add(textClock, BorderLayout.NORTH);
        textClock.setEditable(false);
        add(textScreen, BorderLayout.CENTER);
        textScreen.setEditable(false);
        Panel panel = new Panel();
        panel.add(buttonUse);
        panel.add(buttonAlarm);
        panel.add(buttonPhone);
        panel.add(buttonExit);
        add(panel, BorderLayout.SOUTH);
        pack();
        show();
        buttonUse.addActionListener(this);
        buttonAlarm.addActionListener(this);
        buttonPhone.addActionListener(this);
        buttonExit.addActionListener(this);
    }
    public void actionPerformed(ActionEvent e) {
        System.out.println(e.toString());
        if (e.getSource() == buttonUse) {           
            state.doUse(this);
        } else if (e.getSource() == buttonAlarm) {  
            state.doAlarm(this);
        } else if (e.getSource() == buttonPhone) {  
            state.doPhone(this);
        } else if (e.getSource() == buttonExit) {   
            System.exit(0);
        } else {
            System.out.println("?");
        }
    }
    public void setClock(int hour) {
        String clockstring = "1";
        if (hour < 10) {
            clockstring += "0" + hour + ":00";
        } else {
            clockstring += hour + ":00";
        }
        System.out.println(clockstring);
        textClock.setText(clockstring);
        state.doClock(this, hour);
    }
    public void changeState(State state) {
        System.out.println("2" + this.state + "3" + state + "4");
        this.state = state;
    }
    public void callSecurityCenter(String msg) {
        textScreen.append("call! " + msg + "\n");
    }
    public void recordLog(String msg) {
        textScreen.append("record ... " + msg + "\n");
    }
}

State

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public interface State {
    public abstract void doClock(Context context, int hour);    
    public abstract void doUse(Context context);                
    public abstract void doAlarm(Context context);              
    public abstract void doPhone(Context context);              
}

Main

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public class Main {
    public static void main(String[] args) {
        SafeFrame frame = new SafeFrame("State Sample");
        while (true) {
            for (int hour = 0; hour < 24; hour++) {
                frame.setClock(hour);   
                try {
                    Thread.sleep(1000);
                } catch (InterruptedException e) {
                }
            }
        }
    }
}
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