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package org.javacs;
import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.ArrayBlockingQueue;
import java.util.function.Function;
class LruCache<K, V> {
private final ArrayBlockingQueue<K> fifo;
private final Map<K, V> map;
private final Function<K, V> loader;
LruCache(int capacity, Function<K, V> loader) {
this.fifo = new ArrayBlockingQueue<>(capacity);
this.map = new HashMap<K, V>(capacity);
this.loader = loader;
}
public V get(K key) {
// If we already have key in cache, return it
if (map.containsKey(key)) return map.get(key);
// If we need to make room for another entry, remove the oldest entry
if (fifo.remainingCapacity() == 0) {
var evict = fifo.remove();
map.remove(evict);
}
// Add key to map
map.put(key, loader.apply(key));
fifo.add(key);
return map.get(key);
}
}
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