public int compare(Object o1, Object o2) {
        File file1 = (File)o1;
        File file2 = (File)o2;
        long diff = file1.lastModified() - file2.lastModified();
        if (diff > 0)
            return 1;
        else if (diff == 0)
            return 0;
        else
            return -1
 
;
    }

    public boolean equals(Object obj){
        return true; //簡單做法
    }