'Java code' to add prefix to all files in a specified directory. All you need is to modify two variables. That's it!

AddPrefixToFiles.java

import java.io.File;

/**
 * Created with IntelliJ IDEA.
 * User: Joonhyung
 * Date: 1/6/14
 * Time: 10:20 PM
 * To change this template use File | Settings | File Templates.
 */
public class AddPrefixToFiles {
    public static void main(String[] args) throws Exception {

        // VARIABLE SET UP.
        String directory = "PATH-TO-DIRECTORY HERE!";
        String PREFIX = "PREFIX HERE!";

        // No need to modify the code below.
        File[] files = new File(directory).listFiles();
        for(File file : files){
            if(file.isFile()){
                String ORIGINALNAME = file.getName();
                File NEWFILE = new File(directory+PREFIX+" "+ORIGINALNAME);
                boolean success = file.renameTo(NEWFILE);
                if (!success) {
                    System.err.println("FAILED to rename "+file.getName());
                } else {
                System.out.println(NEWFILE.getName());
                }
            }
        }
    }
}