code: public boolean getBooleanValue(String key, boolean defaultVal) {
          String sValue = readValue(key);
          boolean res = defaultVal;
          if (sValue != null) {
              if ("true".equals(sValue)) {
                  res = true;
              } else if ("false".equals(sValue)) {
                  res = false;
              }
          }
          return res;
      }
docs: Common