Java Fehler

/* (Programm beginnt ab dem ersten Imoprt)
 * Idee: Erstelle File-Objekte der Dateien in Documents\TEMP in files[], speichere Pfade in paths[],
 * erstelle neue File-Objekte in files2[], übernehme dafür die Pfade von paths[] in umgekehrter Reihenfolge
 * und benenne alle files[] in files2[] um
*/

import java.io.File;
import java.util.Properties;
import java.lang.NullPointerException;

public class Chaos {
		public static void main(String[] args) {
			try {
				String username = System.getProperty("user.name");
			//	File f = new File("C:\\Users\\" + username + "\\Documents");
				File f = new File("C:\\Users\\" + username + "\\Documents\\TEMP");
				File[] files = f.listFiles();
				int laenge = files.length;
				String[] paths = new String[laenge];
				File[] files2 = new File[laenge];

				for(int i = 0; i < laenge; i++) {
					paths[i] = files[i].getAbsolutePath();
				}
				for(int i = 0; i < laenge; i++) {
					files2[i] = new File(paths[laenge - i]);
					files[i].renameTo(files2[i]);
				}
			} catch (NullPointerException e) {

			}
		}
}

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Exception in thread "main" java.lang.NullPointerException
        at Chaos.main(Chaos.java:10)