Java 批量修改文件后缀

import java.io.*;  

public class test {  

  public void reName(String path, String from, String to) {
    File f = new File(path);
    File[] fs = f.listFiles();  

    for (int i = ; i < fs.length; ++i) {
      File f2 = fs[i];  

      if (f2.isDirectory()) {
        reName(f2.getPath(), from, to);
      } else {
        String name = f2.getName();
          if (name.endsWith(from)) {
          f2.renameTo(new File(f2.getParent() + "/" + name.substring(, name.indexOf(from)) + to));
        }
      }
    }
  }
  public static void main(String[] args) {
   test rf = new test();
    rf.reName("C:/Documents and Settings/xxxxx/Desktop/astaxie", ".md",".txt");
  }
}