LinkedHashMap's hidden (?) features
Recently I discovered two very nice features of the java.util.LinkedHashMap : accessOrder and removeEldestEntry(Entry) . These features combined let you implement simple LRU caches in under two minutes. accessOrder The accessOrder flag is set when creating the LinkedHashMap instance using the LinkedHashMap(int initialCapacity, float loadFactor, boolean accessOrder) constructor. This boolean flag specifies how the entries in the map are ordered: accessOrder=true The elements are ordered according to their access: When iterating over the map the most recently accessed entry is returned first and the least recently accessed element is returned last. Only the get , put , and putAll methods influence this ordering. accessOrder=false The elements are ordered according to their insertion. This is the default if any of the other LinkedHashMap constructors is used. In this ordering read access to the map has no influence on element ordering. removeEdlestEntry(Entry) The second feature of ...