/**
* Sets the eviction policy strategy. The Cache will use a policy at startup.
* There are three policies which can be configured: LRU, LFU and FIFO. However
* many other policies are possible. That the policy has access to the whole
* element enables policies based on the key, value, metadata, statistics, or a
* combination of any of the above.
*
* It is safe to change the policy of a store at any time. The new policy takes
* effect immediately.
*
* @param policy the new policy
*/
public void setMemoryStoreEvictionPolicy(Policy policy) {
memoryStore.setEvictionPolicy(policy);
}

public interface Policy {
/**
* @return the name of the Policy. Inbuilt examples are LRU, LFU and FIFO.
*/
String getName();
/**
* Finds the best eviction candidate based on the sampled elements. What
* distinguishes this approach from the classic data structures approach is
* that an Element contains metadata (e.g. usage statistics) which can be
* used for making policy decisions, while generic data structures do not.
* It is expected that implementations will take advantage of that
* metadata.
*
* @param sampledElements this should be a random subset of the population
* @param justAdded we probably never want to select the element just added.
* It is provided so that it can be ignored if selected. May be null.
* @return the selected Element
*/
Element selectedBasedOnPolicy(Element[] sampledElements, Element justAdded);
/**
* Compares the desirableness for eviction of two elements
*
* @param element1 the element to compare against
* @param element2 the element to compare
* @return true if the second element is preferable for eviction to the
* first element under ths policy
*/
boolean compare(Element element1, Element element2);
}