code: private static void forceInit(Class<?> cls) {
          try {
              Class.forName(cls.getName(), true, cls.getClassLoader());
          } catch (ClassNotFoundException e) {
              throw new IllegalArgumentException("Can't initialize class " + cls, e);
          }
      }
docs: Force initialization of the static members.
  As of Java 5, referencing a class doesn't force it to initialize. Since
  this class requires that the classes be initialized to declare their
  comparators, we force that initialization to happen.
  
  @param cls the class to initialize