code: public static String joinSizeInfoToKey(String key, int w, int h) {
          if (w > 0 && h != Integer.MAX_VALUE && h > 0 && h != Integer.MAX_VALUE) {
              return new StringBuilder(key).append(SIZE_SP).append(w).append(SIZE_SP).append(h).toString();
          }
          return key;
      }
docs: Join the key and the size information.
  
  @param key
  @param w
  @param h
  @return "$key" + "_" + "$w" + "_" + "$h"