History Map : Map « Collections Data Structure « Java

History Map

// $Id: HistoryMap.java,v 1.11 2003/09/11 12:33:06 larsga Exp $

//package net.ontopia.utils;

import java.util.ArrayList;
import java.util.Collection;
import java.util.HashMap;
import java.util.Iterator;

//import org.slf4j.Logger;
//import org.slf4j.LoggerFactory;

 * INTERNAL: Helper class for storing elements up to a certain amount, lower
 * most elements will be removed to ensure a fixed size of the collection.
 * @since 1.2.5
public class HistoryMap<T> extends HashMap<Integer, T> {
  protected int maxEntries;
  protected boolean suppressDuplicates;
  private int counter;

  // initialization of logging facility
  // private static Logger log =
  // LoggerFactory.getLogger(HistoryMap.class.getName());

   * Default constructor which uses 20 entries as the default history size and
   * does suppress duplicates.
  public HistoryMap() {
    this(20, true);

   * Constructor which allows to specify number of entries to store and
   * duplicate suppression behaviour.
   * @param maxEntries
   *            Maxium number of entries to store in the history.
   * @param suppressDuplicates
   *            Should suppress duplicate entries in map.
  public HistoryMap(int maxEntries, boolean suppressDuplicates) {
    this.maxEntries = maxEntries;
    this.counter = 0;
    this.suppressDuplicates = suppressDuplicates;

  public int getMaxEntries() {
    return maxEntries;

  public boolean doesSuppressDuplicates() {
    return suppressDuplicates;

  public void add(T obj) {
    // do not add if object already exists
    if (suppressDuplicates && containsValue(obj))
    put(new Integer(counter), obj);
    if (size() >= maxEntries)
      try {
        remove(new Integer(counter - maxEntries));
      } catch (Exception e) {
        // log.error("Remove of entry from historymap without success."
        // +
        // e.getMessage());

  public void removeEntry(T obj) {
    Iterator<Integer> it = keySet().iterator();
    // log.info("A removing from history");
    while (it.hasNext()) {
      Integer key = it.next();
      T val = get(key);
      if (val.equals(obj)) {
        // log.info("removing from history " + key);
    } // while it

  public T getEntry(int index) {
    return get(new Integer(counter - size() + index));

  public Collection<T> getEntries() {
    Collection<T> result = new ArrayList<T>();
    for (int i = 1; i <= size(); i++) {
      if (getEntry(i) != null)

    return result;

  public Collection getEntriesReverse() {
    Collection result = new ArrayList();
    for (int i = size(); i >= 1; i--) {
      if (getEntry(i) != null)

    return result;



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