java-design-patterns/feature-toggle/src/main/java/com/iluwatar/featuretoggle/user/UserGroup.java

package com.iluwatar.featuretoggle.user;

import java.util.ArrayList;
import java.util.List;

/**
 * Contains the lists of users of different groups paid and free. Used to demonstrate the tiered example of feature
 * toggle. Allowing certain features to be available to only certain groups of users.
 *
 * @see User
 */
public class UserGroup {

  private static List<User> freeGroup = new ArrayList<>();
  private static List<User> paidGroup = new ArrayList<>();


  /**
   * Add the passed {@link User} to the free user group list.
   *
   * @param user {@link User} to be added to the free group
   * @throws IllegalArgumentException
   * @see User
   */
  public static void addUserToFreeGroup(final User user) throws IllegalArgumentException {
    if (paidGroup.contains(user)) {
      throw new IllegalArgumentException("User all ready member of paid group.");
    } else {
      if (!freeGroup.contains(user)) {
        freeGroup.add(user);
      }
    }
  }

  /**
   * Add the passed {@link User} to the paid user group list.
   *
   * @param user {@link User} to be added to the paid group
   * @throws IllegalArgumentException
   * @see User
   */
  public static void addUserToPaidGroup(final User user) throws IllegalArgumentException {
    if (freeGroup.contains(user)) {
      throw new IllegalArgumentException("User all ready member of free group.");
    } else {
      if (!paidGroup.contains(user)) {
        paidGroup.add(user);
      }
    }
  }

  public static boolean isPaid(User user) {
    return paidGroup.contains(user);
  }
}