CacheStats.java

package lrucache;

import java.util.concurrent.atomic.AtomicLong;

/**
 * Lock-free hit/miss/eviction counters.
 * AtomicLong means reads and writes to these counters never need a lock,
 * keeping the hot path (get/put) as fast as possible.
 */
public class CacheStats {

    private final AtomicLong hits      = new AtomicLong();
    private final AtomicLong misses    = new AtomicLong();
    private final AtomicLong evictions = new AtomicLong();

    void recordHit()      { hits.incrementAndGet(); }
    void recordMiss()     { misses.incrementAndGet(); }
    void recordEviction() { evictions.incrementAndGet(); }

    public long getHits()      { return hits.get(); }
    public long getMisses()    { return misses.get(); }
    public long getEvictions() { return evictions.get(); }

    public double hitRate() {
        long total = hits.get() + misses.get();
        return total == 0 ? 0.0 : (double) hits.get() / total;
    }

    @Override
    public String toString() {
        return String.format("CacheStats{hits=%d, misses=%d, evictions=%d, hitRate=%.2f%%}",
                getHits(), getMisses(), getEvictions(), hitRate() * 100);
    }
}