code: public final boolean setActivity(String activity) throws LockingException {
                  Validate.notNull(activity);
                  Validate.notEmpty(activity);
                  if (isFieldLocked(EntryField.ACTIVITY)) {
                          if (!this.activity.equals(activity)) {
                                  throw new LockingException(EntryField.ACTIVITY);
                          }
                          return false;
                  } else {
                          this.activity = activity;
                          return true;
                  }
          }
docs: Sets the activity of the log entry ({@link #activity}).
  
  @param activity Activity to set.
  @throws LockingException if the field ACTIVITY is locked and the
  given activity differs from the current value of {@link #activity}.
  @return <code>true</code> if {@link #activity} was modified;<br>
  <code>false</code> otherwise.