# lru-cache

Runnable companion for the ankurm.com article
[LRU Cache in Java: LinkedHashMap, HashMap + Doubly Linked List and a Thread-Safe Version](https://ankurm.com/lru-cache-in-java/).

Three LRU caches, three thread-safe variants, a Caffeine reference, a deliberately broken
`ReadWriteLock` version, correctness and stress tests, and a short JMH comparison.

| Component | Version | Verified against |
|---|---|---|
| JDK | 25.0.5+8 (Temurin, LTS) | `java -version` |
| JUnit | 6.1.3 | `maven-metadata.xml` on Maven Central |
| Caffeine | 3.3.1 | `maven-metadata.xml`; GitHub release page lists it as Latest |
| JMH | 1.37 | `maven-metadata.xml` |

```bash
export JAVA_HOME=/path/to/jdk-25 && export PATH="$JAVA_HOME/bin:$PATH"
cd lru-cache
mvn test                 # 43 tests; rewrites output/01-08
./scripts/run-all.sh     # also regenerates output/09 (broken-lock demo) and 10 (JMH)
```

| Source | What it is |
|---|---|
| `LinkedHashMapLruCache` | `LinkedHashMap(accessOrder=true)` + `removeEldestEntry` |
| `HashMapLruCache` | `HashMap` + hand-rolled doubly linked list with sentinel head/tail |
| `SynchronizedLruCache`, `ReentrantLockLruCache` | one coarse lock around variant 2 |
| `StripedLruCache` | N independent segments, LRU per segment (not global) |
| `BrokenReadWriteLockLruCache`, `BrokenLockDemo` | the tempting wrong answer, and what it does |
| `CaffeineLru`, `bench/LruBenchmark` | production reference and the JMH harness |

`output/09` and `output/10` are measurements from a shared 2-vCPU sandbox: indicative, not asserted.