import java.io.File;

/**
 * 启动一个线程，每隔一秒扫描一个指定文件夹，发现里面有其他文件存在就删除,保证该文件夹下只能存在（*.txt）的文件。
 * @author dong007
 *
 */
public class ThreadTxt extends Thread {
    
    /** 指定文件夹路径 */
    private static String PATH = "";
    public void run() {
        File file = new File(PATH);
        File[] fileArray = file.listFiles();
        while (true) {
            try {
                Thread.sleep(1000); // 休眠一秒
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            for (File currFile : fileArray) {
                if (currFile.isFile() && !((currFile.getName()).endsWith(".txt"))) {
                    currFile.delete();
                    System.out.println("此文件夹下非*.txt文件已删除");
                } else if(currFile.isDirectory()){
                    System.out.println("此文件夹下不存在文件");
                } else{
                    System.out.println("结束");
                }
            }
        }
    }
}

import java.io.File;

public class MonitorRunner implements Runnable {
    
    private static String PATH = "";
    
    public void run() {
        File file = new File(PATH);
        File[] fileArray = file.listFiles();
        int before = 0;
        int current = 0;
        while(true) {
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            before = current;
            current = fileArray.length;
            int count = current - before;
            if (count == 0) {
                System.out.println("未进行任何操作");
            } else if (count > 0) {
                System.out.println("新建文件操作");
            } else {
                System.out.println("删除文件操作");
            }
        }
    }
}

public class Main {
    public static void main(String[] args) {
        ThreadTxt threadTxt = new ThreadTxt();
        threadTxt.start();
        
        MonitorRunner monitorRunner = new MonitorRunner();
        Thread monitorThread = new Thread(monitorRunner);
        monitorThread.start();
    }
}