public class ConsumerGroupDescription {
    private final String groupId;
    private final boolean isSimpleConsumerGroup;
    private final Collection<MemberDescription> members;
    private final String partitionAssignor;
    private final GroupType type;
    private final ConsumerGroupState state;
    private final Node coordinator;
    private final Set<AclOperation> authorizedOperations;
	private final Optional<Integer> groupEpoch;
    private final Optional<Integer> targetAssignmentEpoch;

	// ...

	/**
	 * The epoch of the consumer group.
	 */
	public Optional<Integer> groupEpoch() {
		return groupEpoch;
	}

	/**
	 * The epoch of the target assignment.
	 */
	public Optional<Integer> targetAssignmentEpoch() {
		return targetAssignmentEpoch;
	}
}

public class MemberDescription {
    private final String memberId;
    private final Optional<String> groupInstanceId;
    private final String clientId;
    private final String host;
    private final MemberAssignment assignment;
    private final Optional<MemberAssignment> targetAssignment;
    private final Optional<Integer> memberEpoch;

	// ...

	/**
	 * The epoch of the group member.
	 */
	public Optional<Integer> memberEpoch() {
		return memberEpoch;
	}
}