Cache Map : Customized Map « Collections Data Structure « Java

Cache Map

 * Copyright (c) 2007, 2008 IBM Corporation and Others
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * Contributors:
 *    Hisashi MIYASHITA - initial API and implementation
 *    Kentarou FUKUDA - initial API and implementation

import java.util.Iterator;
import java.util.LinkedList;
import java.util.NoSuchElementException;
import java.util.SortedMap;
import java.util.TreeMap;

 * Utility class for cache map.
public class CacheMap extends TreeMap<String, Object> {
  private static final long serialVersionUID = 6681131647931821052L;

  private final int maxSize;
  private final int evictSize;

  private final LinkedList<Object> accessList = new LinkedList<Object>();

   * Constructor of cache map. If the map exceed the maximum size, the
   * key/value sets will be removed from map based on specified evict size.
   * @param maxSize
   *            maximum size of the map
   * @param evictSize
   *            number of evict object
  public CacheMap(int maxSize, int evictSize) {
    this.maxSize = maxSize;
    this.evictSize = evictSize;

  private void evict() {
    Iterator<Object> it = accessList.iterator();
    for (int i = 0; i < evictSize; i++) {
      if (!it.hasNext())
      Object key =;

  private int searchAccessList(Object key) {
    return accessList.indexOf(key);

  private void accessEntry(Object key) {
    int idx = searchAccessList(key);
    if (idx >= 0) {

  public Object put(String key, Object val) {
    if (size() >= maxSize)
    return super.put(key, val);

  public Object get(Object key) {
    return super.get(key);

   * Search a key that starts with the specified prefix from the map, and
   * return the value corresponding to the key.
   * @param prefix
   *            target prefix
   * @return the value whose key starts with prefix, or null if not available
  public Object matchStartsWith(String prefix) {
    SortedMap<String, Object> smap = super.tailMap(prefix);
    Object okey;
    try {
      okey = smap.firstKey();
    } catch (NoSuchElementException e) {
      return null;
    if (!(okey instanceof String))
      return null;
    String key = (String) okey;
    // System.err.println("MSW:" + key + " / " + prefix);
    if (!key.startsWith(prefix))
      return null;
    return super.get(key);


Related examples in the same category

1.Ordered Map
2.Case Insensitive Map
3.A Map collection with real-time behavior
4.Map implementation Optimized for Strings keys
5.An integer hashmap
6.An IdentityMap that uses reference-equality instead of object-equality
7.Int Object HashMap
8.Concurrent Skip List Map
9.A hash map that uses primitive ints for the key rather than objects.
10.Integer Map
11.Copy On Write Map
12.Expiring Map
13.Array Map
14.Int Object HashMap (from CERN)
15.Int HashMap from
16.String Map
17.List Map
18.Map using Locale objects as keys
19.Map with keys iterated in insertion order
20.Most Recently Used Map
21.Multi Map
22.MultiMap is a Java version of the C++ STL class std::multimap
23.Object Int Map
24.Sequenced HashMap
25.Int Int Map
26.Int Object Map
27.Identity HashMap
28.A java.util.Map interface which can only hold a single object
29.A multi valued Map
30.A simple hashmap from keys to integers
31.A memory-efficient hash map.
32.An implementation of the java.util.Map interface which can only hold a single object.
33.Utility methods for operating on memory-efficient maps.
34.CaseBlindHashMap - a HashMap extension, using Strings as key values.
35.A fixed size map implementation.
36.Int HashMap
37.IntMap provides a simple hashmap from keys to integers
38.Complex Key HashMap
39.A Map with multiple values for a key
40.A Map that accepts int or Integer keys only
41.A Map where keys are compared by object identity, rather than equals()
42.Type-safe Map, from char array to String value
43.A hashtable-based Map implementation with soft keys
44.List ordered map
45.Hash map using String values as keys mapped to primitive int values.
46.Lookup table that stores a list of strings
47.HashNMap stores multiple values by a single key value. Values can be retrieved using a direct query or by creating an enumeration over the stored elements.
48.Combines multiple values to form a single composite key. MultiKey can often be used as an alternative to nested maps.