code: public boolean insertUser(String name)
  	{
  		if (isUserExist(name))
  		{
  			throw new SystemException(String.format("User '%s' already exist.", name));
  		}
  
  		return allUsers.add(name);
  	}
docs: <p>insertUser.</p>
  
  @param name a {@link java.lang.String} object.
  @return a boolean.