code: public String getString(String key) {
  
          if (key == null) {
              throw new NullPointerException("Missing resource key.");
          }
  
          PropertyBundle p = this;
  
          do {
              String value = p.key2values.get(key);
              if (value != null) {
                  return value;
              }
          } while ((p = p.parent) != null);
  
          throw new MissingResourceException(
              "Cannot find property resource for: " + toResourceName(this.baseName, this.bundleLocale) + "=>" + key,
              PropertyBundle.class.getName(),
              key);
  
      }
docs: /*[deutsch]
  <p>Liefert den mit dem angegebenen Schl&uuml;ssel verkn&uuml;pften Eigenschaftenwert. </p>
  
  @param   key     the key of property resource
  @return  the value associated with given key
  @throws  MissingResourceException if the value cannot be found