線程之旅–Balking Pattern Producer

假設有自動儲存這種功能，當儲存資料時，之前的資料會被覆蓋，而只有最新的資料會被存下來，那麼相同的資料儲存，那麼這就是儲存的操作就是多餘了的，那麼以下這個範例將類似於word的自動儲存功能，只是此範例為最最精簡版

此範例由4個檔案組成

Main.java--程式調用類

public class Main {
    public static void main(String[] args) {
        Data data = new Data("data.txt", "(empty)");
        new ChangerThread("ChangerThread", data).start();
        new SaverThread("SaverThread", data).start();
    }
}

Data.java--可修改、可儲存資料的類

import java.io.IOException;
import java.io.FileWriter;
import java.io.Writer;

public class Data {
  
    private String filename;    //修改是的名字
    private String content;     // 資料的內容
    private boolean changed;    //修改後的內容還沒儲存的話，值為true

    public Data(String filename, String content) {
        this.filename = filename;
        this.content = content;
        this.changed = true;
    }

    // 修改資料內容
    public synchronized void change(String newContent) {       
        content = newContent;                                  
        changed = true;                                          
    }                                                          

    // 若有資料修改，就儲存到擋安裡
    public synchronized void save() throws IOException {     
        if (!changed) {                                          
            System.out.println(Thread.currentThread().getName() + " balks");
            return;                                            
        }                                                      
        doSave();                                            
        changed = false;                                         
    }                                                          

    // 實際資料儲存到擋案裡用的方法
    private void doSave() throws IOException {
        System.out.println(Thread.currentThread().getName() + " calls doSave, content = " + content);
        Writer writer = new FileWriter(filename);
        writer.write(content);
        writer.close();
    }
}

ChanagerThread.java   ---用來修改儲存資料屬性的類

import java.io.IOException;
import java.util.Random;

public class ChangerThread extends Thread {
    private Data data;
    private Random random = new Random();
    public ChangerThread(String name, Data data) {
        super(name);
        this.data = data;
    }
    public void run() {
        try {
            for (int i = 0; true; i++) {
                data.change("No." + i);             //修改資料
                Thread.sleep(random.nextInt(1000)); // 類比去做別的事情
                data.save();                        // 明確的要求存檔
            }
        } catch (IOException e) {
            e.printStackTrace();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

ServerThread.java--定期儲存資料屬性的類

import java.io.IOException;

public class SaverThread extends Thread {
    private Data data;
    public SaverThread(String name, Data data) {
        super(name);
        this.data = data;
    }
    public void run() {
        try {
            while (true) {
                data.save();            // 儲存資料
                Thread.sleep(1000);     // 休息約1秒
            }
        } catch (IOException e) {
            e.printStackTrace();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}