org.sirix.cache.KeyCache Maven / Gradle / Ivy
package org.sirix.cache;
import java.util.ArrayList;
import java.util.Collection;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;
/**
* An LRU cache, based on LinkedHashMap holding last key changes for a user.
*
* @author Patrick Lang, University of Konstanz
*/
public final class KeyCache {
/**
* Capacity of the cache.
*/
static final int CACHE_CAPACITY = 100;
/**
* The collection to hold the maps.
*/
private final Map> mMap;
/**
* Constructor creates a new key cache.
*/
public KeyCache() {
mMap = new LinkedHashMap>(CACHE_CAPACITY) {
private static final long serialVersionUID = 1;
@Override
protected boolean removeEldestEntry(final Map.Entry> mEldest) {
boolean returnVal = false;
if (size() > CACHE_CAPACITY) {
returnVal = true;
}
return returnVal;
}
};
}
/**
* Returns the stored LinkedList of corresponding user.
*
* @param user User key.
* @return linked list of user.
*/
public final List get(final String user) {
final List list = mMap.get(user);
return list; // returns null if no value for this user exists in cache.
}
/**
* Stores a new entry in cache consisting of a user name as key and a linked list for storing node
* keys as value.
*
* @param user user name as key.
* @param list linked list as values.
*/
public final void put(final String user, final List list) {
mMap.put(user, list);
}
/**
* Clears the cache.
*/
public final void clear() {
mMap.clear();
}
/**
* Returns the number of used entries in the cache.
*
* @return the number of entries currently in the cache.
*/
public final int usedEntries() {
return mMap.size();
}
/**
* Returns a Collection that contains a copy of all cache entries.
*
* @return a Collection with a copy of the cache content.
*/
public final Collection>> getAll() {
return new ArrayList>>(mMap.entrySet());
}
}