ObjectExemplarRegistry.java

/*
 * aitools utilities
 * Copyright (C) 2006 Noel Bush
 *
 * 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 Street, Fifth Floor, Boston, MA  02110-1301  USA
 */

package org.aitools.util;

import java.util.Hashtable;

/**
 * Similar to {@link ClassRegistry}, but registers object exemplars.
 * 
 * @param <B> the base class for objects that will be registered
 */
abstract public class ObjectExemplarRegistry<B> {

  /** The type of B (why, oh why, should I have to do this? */
  private Class<B> type;

  /** The Hashtable that stores the objects. */
  protected Hashtable<String, B> registry;

  /**
   * Loads the registry with a set of exemplar objects.
   * 
   * @param classnames the classnames for which to register exemplar objects
   * @param objectType the type of B (seems stupid to have to pass this in, but necessary to avoid some compiler errors)
   * @param constructorArguments the arguments for B's constructor
   */
  public ObjectExemplarRegistry(String[] classnames, Class<B> objectType, Object... constructorArguments) {
    this.type = objectType;

    // Initialize the backing Hashtable.
    this.registry = new Hashtable<String, B>(classnames.length);

    // Create and register exemplar objects.
    for (int index = classnames.length; --index >= 0;) {
      this.register(classnames[index], constructorArguments);
    }
  }

  /**
   * A wrapper for the internal HashSet's get method.
   * 
   * @param classname the classname for which an exemplar object is desired
   * @return the registered exemplar object corresponding to the classname
   */
  public synchronized B get(String classname) {
    if (this.registry.containsKey(classname)) {
      return this.registry.get(classname);
    }
    throw new NullPointerException(String.format("Object registry does not contain an instance of \"%s\".", classname));
  }

  /**
   * Registers an individual exemplar object.
   * 
   * @param classname the name of the object to register
   * @param constructorArguments the arguments to the constructor
   */
  public void register(String classname, Object... constructorArguments) {
    // Create an instance of the class.
    B exemplar = Classes.getSubclassInstance(this.type, classname, classname, constructorArguments);

    // Register an instance of the class.
    this.registry.put(classname, exemplar);
  }
}