今天我想实现一个定数的map,搜索Java Map的实现类,发现了下面的说明:


LinkedHashMap provides two capabilities that are not available with LinkedHashSet. When you create a LinkedHashMap, you can order it based on key access rather than insertion. In other words, merely looking up the value associated with a key brings that key to the end of the map. Also, LinkedHashMap provides the removeEldestEntry method, which may be overridden to impose a policy for removing stale mappings automatically when new mappings are added to the map. This makes it very easy to implement a custom cache.

For example, this override will allow the map to grow up to as many as 100 entries and then it will delete the eldest entry each time a new entry is added, maintaining a steady state of 100 entries.

private static final int MAX_ENTRIES = 100;

protected boolean removeEldestEntry(Map.Entry eldest) {
    return size() > MAX_ENTRIES;
Written on October 10, 2017