使用RandomAccessFile和多线程来实现开启三个线程去复制一个文件

题目：使用RandomAccessFile和多线程来实现开启三个线程去复制一个文件
代码：
package Down;

import java.io.File;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.RandomAccessFile;

public class DownLoadDemo {
public static void main(String[] args) {
File src = new File(“E:\qqq.txt”);
File dst = new File(“E:\ppp.txt”);
DownloadUtil downloadUtil = new DownloadUtil(src, dst, 3);
downloadUtil.download();
}
}

// 下载工具类
class DownloadUtil {
private File src;// 源文件
private File dst;// 目标文件
private int threadNum;// 线程数量

public DownloadUtil(File src, File dst, int threadNum) {    super();    this.src = src;    this.dst = dst;    this.threadNum = threadNum;}// 开启多线程下载public void download() {    // 循环开多个线程    for (int i = 0; i < threadNum; i++) {        DownloadThread thread = new DownloadThread(i);        thread.setName("线程" + (i + 1));        thread.start();    }}// 定义一个下载线程class DownloadThread extends Thread {    // private int index；/表示第几个线程    // 每一个线程要下载的文件大小    // 如果不能平方，则每一份+1，确保下载完整个文件    private long BlockSize = src.length() % threadNum == 0 ? src.length() / threadNum            : src.length() / threadNum + 1;    // 起始位置    private long startPos;    public DownloadThread(int index) {        // this。index = index;        // 计算初始位置        startPos = BlockSize * index;    }    public void run() {        super.run();        try {            // 要读入的文件            RandomAccessFile rafR = new RandomAccessFile(src, "r");            // 要写入的文件            RandomAccessFile rafW = new RandomAccessFile(dst, "rw");            rafR.seek(startPos);            rafW.seek(startPos);            int bufSize = 1024 * 1024;// 缓冲区大小            byte[] buf = new byte[bufSize];// 缓冲区            int len = -1;            do {                len = (int) (BlockSize > bufSize ? bufSize : BlockSize);                rafR.read(buf, 0, len);                rafW.write(buf, 0, len);                BlockSize -= len;                System.out.println(Thread.currentThread().getName() + "读取了" + len + "字节");            } while (BlockSize > 0);            rafR.close();            rafW.close();            System.out.println(Thread.currentThread().getName() + "下载完毕");        } catch (FileNotFoundException e) {            e.printStackTrace();        } catch (IOException e) {            e.printStackTrace();        }    }}

}