Java實現，用HashMap儲存關係{key值 : 命中次數與上次命中時間}，當需要淘汰某個key值時，呼叫map.remove(key)。

import java.util.*;
 
public class LFUAgingMap<K, V> extends HashMap<K, V> {
    private static final int DEFAULT_MAX_SIZE = 3;
    private int maxSize = DEFAULT_MAX_SIZE;
    Map<K, HitRate> km = new HashMap<K, HitRate>();
 
    public LFUAgingMap() {
        this(DEFAULT_MAX_SIZE);
    }
 
    public LFUAgingMap(int maxSize) {
        super(maxSize);
        this.maxSize = maxSize;
    }
 
    @Override
    public V get(Object key) {
        V v = super.get(key);
        if (v != null) {
            HitRate hitRate = km.get(key);
            hitRate.hitCount += 1;
            hitRate.atime = System.nanoTime();
        }
        return v;
    }
 
    @Override
    public V put(K key, V value) {
        while (km.size() >= maxSize) {
            K k = getLFUAging();
            km.remove(k);
            this.remove(k);
        }
        V v = super.put(key, value);
        km.put(key, new HitRate(key, 1, System.nanoTime()));
        return v;
    }
 
    private K getLFUAging() {
        HitRate min = Collections.min(km.values());
        return min.key;
    }
 
    class HitRate implements Comparable<HitRate> {
        K key;
        Integer hitCount; // 命中次數
        Long atime; // 上次命中時間
 
        public HitRate(K key, Integer hitCount, Long atime) {
            this.key = key;
            this.hitCount = hitCount;
            this.atime = atime;
        }
 
        @Override
        public int compareTo(HitRate o) {
            int hr = hitCount.compareTo(o.hitCount);
            return hr != 0 ? hr : atime.compareTo(o.atime);
        }
    }
    public static void main(String[] as) throws Exception {
        LFUAgingMap<String, String> cache = new LFUAgingMap<String, String>();
        cache.put("a", "a");
        cache.put("b", "b");
        cache.put("c", "c");
 
        cache.get("a");
        cache.get("a");
 
        cache.put("d", "d");
        cache.get("d");
        cache.get("c");
        cache.put("e", "e");
 
        for (String key : cache.keySet()) {
            System.out.println(key);
        }
    }
}