java-interview-lab/lru-cache

lru-cache

Runnable companion for the ankurm.com article LRU Cache in Java: LinkedHashMap, HashMap + Doubly Linked List and a Thread-Safe Version.

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

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.