code: /* LanguageTool, a natural language style checker 
   * Copyright (C) 2016 Daniel Naber (http://www.danielnaber.de)
   * 
   * This library is free software; you can redistribute it and/or
   * modify it under the terms of the GNU Lesser General Public
   * License as published by the Free Software Foundation; either
   * version 2.1 of the License, or (at your option) any later version.
   *
   * This library is distributed in the hope that it will be useful,
   * but WITHOUT ANY WARRANTY; without even the implied warranty of
   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   * Lesser General Public License for more details.
   *
   * You should have received a copy of the GNU Lesser General Public
   * License along with this library; if not, write to the Free Software
   * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301
   * USA
   */
  package org.languagetool.rules;
  
  import java.util.Objects;
  
  /**
   * Identifier for a category.
   * @since 3.3
   */
  public class CategoryId {
    
    private final String id;
  
    public CategoryId(String id) {
      Objects.requireNonNull(id, "Category id must not be null.");
      if (id.trim().isEmpty()) {
        throw new IllegalArgumentException("Category id must not be empty: '" + id + "'");
      }
      this.id = id;
    }
  
    @Override
    public boolean equals(Object o) {
      if (this == o) return true;
      if (o == null || getClass() != o.getClass()) return false;
      CategoryId other = (CategoryId) o;
      return id.equals(other.id);
    }
  
    @Override
    public int hashCode() {
      return id.hashCode();
    }
  
    @Override
    public String toString() {
      return id;
    }
  }
  