code: public boolean getBoolean(String attribute) {
          String s = get(attribute);
          if ("true".equals(s) || "1".equals(s)) {
              return true;
          } else
          if ("false".equals(s) || "0".equals(s)) {
              return false;
          }
          throw new IllegalArgumentException("Attribute " + attribute + " is non-boolean");
      }
docs: Retrieve a value of a boolean attribute.
  Throws IllegalArgumentException if the attribute is missing or not of type boolean.
  @param attribute the attribute name
  @return the value