将虚拟数据写入外部存储android的选定文件

Question

在下面提到的代码中，我将虚拟数据写入外部存储器中的所有文件并重命名为“abc.txt”。但我想要的是只将虚拟数据写入我选择的文件并重命名该特定文件。我该怎么办？

File[] files = root.listFiles();
for ( File f : files ) {
    if (f.isDirectory()) 
        continue;
    FileChannel rwChannel = new RandomAccessFile(f, "rw").getChannel();  
    int numBytes = (int)rwChannel.size();  
    ByteBuffer buffer = rwChannel.map(FileChannel.MapMode.READ_WRITE, 0, numBytes); 
    System.out.println("buffer"+buffer);
    byte[] randomBytes = new byte[numBytes];  
    new Random().nextBytes(randomBytes);  
    buffer.put(randomBytes);  
    rwChannel.write(buffer);
    rwChannel.close(); 
}
File root1 = android.os.Environment.getExternalStorageDirectory();
File[] files1 = root.listFiles();
for ( File f : files ) {
    if (f.isDirectory()) 
        continue;
    File myFile1 = new File(root,"abc.txt");
    f.renameTo(myFile1);
}