package com.atlassian.sal.api.user;
   
   import javax.annotation.Nonnull;
   import java.io.Serializable;
   
   import static com.google.common.base.Preconditions.checkNotNull;
   
   /**
    * Represents an identifier that uniquely identifies a user for the duration of its existence.
   *
   * @since v2.10
   */
  public final class UserKey implements Serializable {
      private static final long serialVersionUID = 1L;
  
      private final String userkey;
  
      /**
       * Default constructor: builds a UserKey from its string representation.
       *
       * @param userkey the string representation of a UserKey. Must not be null.
       */
      public UserKey(@Nonnull final String userkey) {
          checkNotNull(userkey, "userkey");
          this.userkey = userkey;
      }
  
      /**
       * Returns a string representation of the current key.
       *
       * @return a string representation of the current key
       */
      @Nonnull
      public String getStringValue() {
          return userkey;
      }
  
      @Override
      public String toString() {
          return getStringValue();
      }
  
      @Override
      public boolean equals(Object o) {
          if (this == o) {
              return true;
          }
          if (o == null || getClass() != o.getClass()) {
              return false;
          }
  
          UserKey userKey = (UserKey) o;
  
          if (userkey != null ? !userkey.equals(userKey.userkey) : userKey.userkey != null) {
              return false;
          }
  
          return true;
      }
  
      @Override
      public int hashCode() {
          return userkey != null ? userkey.hashCode() : 0;
      }
  
      //
      // Factory methods
      //
  
      /**
       * Builds a {@link UserKey} object from a long id. The id will be converted to a String first.
       *
       * @param userId a user ID
       * @return a {@link UserKey} object
       */
      public static UserKey fromLong(long userId) {
          return new UserKey(String.valueOf(userId));
      }
  }