code: public static MathUtil getInstance() {
  
      if (instance == null) {
        synchronized (MathUtilImpl.class) {
          if (instance == null) {
            MathUtilImpl impl = new MathUtilImpl();
            impl.initialize();
            instance = impl;
          }
        }
      }
      return instance;
    }
docs: This method gets the singleton instance of {@link MathUtil}. <br>
  <b>ATTENTION:</b><br>
  Please prefer dependency-injection instead of using this method.
  
  @return the singleton instance.