code: public static boolean register(String groupName, EndpointGroup endpointGroup,
                                     EndpointSelectionStrategy endpointSelectionStrategy) {
          groupName = normalizeGroupName(groupName);
          if (!GROUP_NAME_PATTERN.matcher(groupName).matches()) {
              throw new IllegalArgumentException(
                      "groupName: " + groupName + " (expected: " + GROUP_NAME_PATTERN.pattern() + ')');
          }
  
          requireNonNull(endpointGroup, "group");
          requireNonNull(endpointSelectionStrategy, "endpointSelectionStrategy");
  
          final EndpointSelector oldSelector = serverGroups.put(
                  groupName, endpointSelectionStrategy.newSelector(endpointGroup));
  
          return oldSelector == null;
      }
docs: Registers the specified {@link EndpointGroup}. If there's already an {@link EndpointGroup} with the
  specified {@code groupName}, this method will replace it with the new one.
  
  @param groupName the case-insensitive name of the {@link EndpointGroup} that matches
  the regular expression {@code /^[-_.0-9a-zA-Z]+$/}
  @param endpointGroup the {@link EndpointGroup} to register
  @param endpointSelectionStrategy the {@link EndpointSelectionStrategy} of the registered group
  
  @return {@code true} if there was no {@link EndpointGroup} with the specified {@code groupName}.
  {@code false} if there was already an {@link EndpointGroup} with the specified {@code groupName}
  and it has been replaced with the new one.