multiset.java

Rakiura JFern是一个非常轻型的带有模拟器的Petri网络框架

// This is copyrighted source file, part of Rakiura JFern package. 
// See the file LICENSE for copyright information and the terms and conditions
// for copying, distributing and modifications of Rakiura JFern package.
// Copyright (C) 1999-2002 by Mariusz Nowostawski and others  [http://www.rakiura.org]

package org.rakiura.cpn;

/**/
import java.util.AbstractCollection;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Iterator;
import java.util.List;


/**
 * Represents a bag of tokens, a multiset. 
 * This is the actual implementation of a multiset. This is one of the basic
 * datastructures of JFern Petri net. Used to store and manipulate
 * tokens. Tokens in JFern are any valid Java datatypes, i.e. any 
 * Java Object can be treated as a token, and can be inserted and
 * removed from the multiset. 
 * 
 *<br><br>
 * Multiset.java<br>
 * Created: Mon Sep 25 10:51:00 2000<br>
 *
 *@author  <a href="[e-mail]">Mariusz Nowostawski</a>
 *@version 2.1.0 $Revision: 1.11 $
 *@since 1.0
 */
public class Multiset extends AbstractCollection {

  /** TODO:  Re-implement this class to use faster more efficient storage. */
  private List store = new ArrayList();

  /**
   * Creates empty multiset. */
  public Multiset() {}

  /**
   * Creates new multiset initialized with a given single element.
   *@param aToken an initial element for this multiset.
   */
  public Multiset(final Object aToken) {
    this.store.add(aToken);
  }

  /**
   * Creates new multiset initialized with elements from 
   * a given collection.
   *@param aCollection initial elements for this multiset.
   */
  public Multiset(final Collection aCollection) {
    this.store.addAll(aCollection);
  }

  /**
   * Adds a token to this multiset.
   *@param aToken token to be added.
   */
  public boolean add(final Object aToken) {
    return this.store.add(aToken);
  }

  /**
   * Removes the first occurance of the specified element 
   * from this multiset.
   *@param aToken token to be removed
   *@return <code>true</code> if the element was removed, 
   * <code>false</code> if the token was not present in this multiset.
   */
  public boolean remove(final Object aToken) {
    return this.store.remove(aToken);
  }

  /**
   * Counts the tokens in this multiset.
   *@return the number of tokens in this bag. 
   */
  public int size() {
    return this.store.size();
  }

  /**
   * Returns an iterator over elements of this bag. 
   *@return iterator over elements of this bag.
   */
  public Iterator iterator() {
    return this.store.iterator();
  }

  /**
   * Returns a random value from this multiset. 
   * This is a convenience method, useful to access 
   * a single token value from a multiset. If the multiset has
   * more than one token an arbitrary token is picked.
   *@return a randomly picked token.
   */
  public Object getAny() {
    if (this.store.size() > 0) {
      // ================================================== reimplement it to use random number generator
      return this.store.get(0);
    } else {
      return null;
    }
  }

  /**
   * Returns <code>n</code> random tokens from this multiset. 
   * This is a convenience method, useful to access 
   * <code>n</code> tokens from a multiset. 
   *@param aNumber a number of randomly selected tokens
   *@return a multiset with <code>n</code> randomly picked tokens.
   */
  public Multiset getAny(final int aNumber) {
    // ================================================== reimplement it to use random number generator
    final Multiset result = new Multiset();
    for (int i = 0; i < aNumber; i++) {
      result.add(this.store.get(i));
    }
    return result;
  }
  

} // Multiset
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