Writing dummy contents in files of external storage android

See more:

Java

Mobile

Android

file

In the below mentioned code I am writing dummy contents in a file called "testfile.txt". But I want to write dummy contents in any of the files of the external storage. I don't want the file name to be hard coded. How do I do?

String root = android.os.Environment.getExternalStorageDirectory().getPath();
File myFile = new File(root,"testfile.txt");

FileChannel rwChannel = new RandomAccessFile(myFile, "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();