The properties iterator iterates over a set of enumerated properties. : Properties « Collections « Java Tutorial

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/**
 * 
 * JFreeReport : a free Java reporting library
 * 
 *
 * Project Info:  http://reporting.pentaho.org/
 *
 * (C) Copyright 2001-2007, by Object Refinery Ltd, Pentaho Corporation and Contributors.
 *
 * 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., 59 Temple Place, Suite 330,
 * Boston, MA 02111-1307, USA.
 *
 * [Java is a trademark or registered trademark of Sun Microsystems, Inc.
 * in the United States and other countries.]
 *
 * ------------
 * PropertiesIterator.java
 * ------------
 * (C) Copyright 2001-2007, by Object Refinery Ltd, Pentaho Corporation and Contributors.
 */

import java.util.Iterator;
import java.util.Properties;

/**
 * The properties iterator iterates over a set of enumerated properties. The
 * properties are named by an optional prefix plus a number, which is counted up
 * on each iteration: <p/>
 * <ul>
 * <li>prefix_0 </li>
 * <li>prefix_1 </li>
 * <li>prefix_2 </li>
 * <li>... </li>
 * </ul>
 * <p/> The iterator iterates over all subsequent numbered proprties until the
 * number-sequence is finished.
 * 
 * @author Thomas Morgner
 * 
 */
public class PropertiesIterator implements Iterator {
  /**
   * The underlying properties collection.
   */
  private Properties properties;

  /**
   * The property name prefix.
   */
  private String prefix;

  /**
   * An incremental counter.
   */
  private int count;

  /**
   * Creates a new properties iterator without an prefix.
   * 
   * @param properties
   *          the underlying properties collection.
   */
  public PropertiesIterator(final Properties properties) {
    this(properties, null);
  }

  /**
   * Creates a new properties iterator with the given prefix.
   * 
   * @param properties
   *          the underlying properties collection.
   * @param prefix
   *          a prefix for generating property names (null permitted).
   */
  public PropertiesIterator(final Properties properties, final String prefix) {
    if (properties == null) {
      throw new NullPointerException();
    }
    this.properties = properties;
    this.prefix = prefix;
    this.count = 0;
  }

  /**
   * Returns true if there is a property in the underlying collection with a
   * name that matches the name returned by the getNextKey() method.
   * 
   * @return true if there is another property with a name in the correct form.
   */
  public boolean hasNext() {
    return properties.containsKey(getNextKey());
  }

  /**
   * Generates a property name in the form <prefix>
   * &lt;count&gt;.
   * 
   *  The &lt;count&gt; begins at 0,
   *  and is automatically incremented with each call to the next() method.
   * 
   *  @return the next key in the sequence
   * 
   */
  private String getNextKey() {
    if (prefix == null) {
      return String.valueOf(count);
    }
    return prefix + String.valueOf(count);
  }

  /**
   * Returns the property with a name the same as the name generated by the
   * getNextKey() method, or null if there is no such property (that is, then
   * end of the sequence has been reached).
   * 
   * @return the property or null.
   */
  public Object next() {
    final String value = properties.getProperty(getNextKey());
    count++;
    return value;
  }

  /**
   * Always throws UnsupportedOperationException as remove is not implemented
   * for this iterator.
   * 
   * @throws UnsupportedOperationException
   *           as remove is not supported.
   */
  public void remove() {
    throw new UnsupportedOperationException();
  }

}