四线程同时拷贝文件！

 package com.softeem.thread.test;import java.io.File;import java.io.FileNotFoundException;import java.io.IOException;import java.io.RandomAccessFile;public class HomeWork3 implements Runnable{ private File files; private File filed; private long l=0; public HomeWork3(String src,String des) { files =new File(src); filed =new File(des+files.getName()); } public void run() { RandomAccessFile raf; try { raf = new RandomAccessFile(files,"rw"); RandomAccessFile raf2=new RandomAccessFile(filed,"rw"); int n=0; synchronized("k") { raf.seek(l); raf2.seek(l); l=l+files.length()/4; System.out.println(l); } int k=0;//标注已经读了多少个字节。 byte by[]=new byte[512]; while((n=raf.read(by))!=-1) { raf2.write(by,0,n); k=k+n; if(k>files.length()/4) { break; } } } catch (FileNotFoundException e) { // TODO Auto-generated catch block e.printStackTrace(); } catch (IOException e) { // TODO Auto-generated catch block e.printStackTrace(); } } public static void main(String args []) { HomeWork3 h=new HomeWork3("D://movie//***//《***》国语第01集.rmvb","F://***的//算法//"); new Thread(h,"0").start(); new Thread(h,"1").start(); new Thread(h,"2").start(); new Thread(h,"3").start(); }}