Question about LRU Cache implementation in Java

Question

The standard example for implementing LRU Cache in Java points to the example depot url http://www.exampledepot.com/egs/java.util/coll_Cache.html

How is removeEldestEntry called by default after just adding a new entry in the code snippet below?

final int MAX_ENTRIES = 100;
Map cache = new LinkedHashMap(MAX_ENTRIES+1, .75F, true) {
    // This method is called just after a new entry has been added
    public boolean removeEldestEntry(Map.Entry eldest) {
        return size() > MAX_ENTRIES;
    }
};

// Add to cache
Object key = "key";
cache.put(key, object);

// Get object
Object o = cache.get(key);
if (o == null && !cache.containsKey(key)) {
    // Object not in cache. If null is not a possible value in the cache,
    // the call to cache.contains(key) is not needed
}

// If the cache is to be used by multiple threads,
// the cache must be wrapped with code to synchronize the methods
cache = (Map)Collections.synchronizedMap(cache);

Answer 1

In this example, the LinkedHashMap is being extended with an "anonymous inner class".

The removeEldestEntry method is overriding the super-class's version, which always returns false (indicating the eldest entry should not be removed). The overriding version returns true if the size of the map exceeds the limit, indicating that the oldest entry should be removed.