@@ -201,7 +201,7 @@ private void evictExpired() {
 while (it.hasNext()) {
 K k = it.next();
 CacheEntry<V> entry = cache.get(k);
-if (entry.isExpired()) {
+if (entry != null && entry.isExpired()) {
 it.remove();
 cache.remove(k);
 notifyEviction(k, entry.value);
@@ -248,7 +248,11 @@ private void notifyEviction(K key, V value) {
 */
 public long getHits() {
 lock.lock();
-try { return hits; } finally { lock.unlock(); }
+try {
+return hits;
+} finally {
+lock.unlock();
+}
 }
 
 /**
@@ -258,7 +262,11 @@ public long getHits() {
 */
 public long getMisses() {
 lock.lock();
-try { return misses; } finally { lock.unlock(); }
+try {
+return misses;
+} finally {
+lock.unlock();
+}
 }
 
 /**
@@ -300,8 +308,7 @@ public String toString() {
 visible.put(entry.getKey(), entry.getValue().value);
 }
 }
-return String.format("Cache(capacity=%d, size=%d, hits=%d, misses=%d, entries=%s)",
-capacity, visible.size(), hits, misses, visible);
+return String.format("Cache(capacity=%d, size=%d, hits=%d, misses=%d, entries=%s)", capacity, visible.size(), hits, misses, visible);
 } finally {
 lock.unlock();
 }

@@ -1,39 +1,40 @@
 package com.thealgorithms.datastructures.caches;
 
-import org.junit.jupiter.api.BeforeEach;
-import org.junit.jupiter.api.Test;
-import org.junit.jupiter.api.function.Executable;
-
-import java.util.ArrayList;
-import java.util.List;
-import java.util.Random;
-
 import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertFalse;
 import static org.junit.jupiter.api.Assertions.assertNull;
 import static org.junit.jupiter.api.Assertions.assertThrows;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 
+import java.util.ArrayList;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Random;
+import java.util.Set;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.function.Executable;
+
 class RRCacheTest {
 
 private RRCache<String, String> cache;
-private List<String> evictedKeys;
+private Set<String> evictedKeys;
 private List<String> evictedValues;
 
 @BeforeEach
 void setUp() {
-evictedKeys = new ArrayList<>();
+evictedKeys = new HashSet<>();
 evictedValues = new ArrayList<>();
 
 cache = new RRCache.Builder<String, String>(3)
-.defaultTTL(1000)
-.random(new Random(0))
-.evictionListener((k, v) -> {
-evictedKeys.add(k);
-evictedValues.add(v);
-})
-.build();
+.defaultTTL(1000)
+.random(new Random(0))
+.evictionListener((k, v) -> {
+evictedKeys.add(k);
+evictedValues.add(v);
+})
+.build();
 }
 
 @Test
@@ -148,11 +149,7 @@ void testBuilderNullEvictionListenerThrows() {
 
 @Test
 void testEvictionListenerExceptionDoesNotCrash() {
-RRCache<String, String> listenerCache = new RRCache.Builder<String, String>(1)
-.evictionListener((k, v) -> {
-throw new RuntimeException("Exception");
-})
-.build();
+RRCache<String, String> listenerCache = new RRCache.Builder<String, String>(1).evictionListener((k, v) -> { throw new RuntimeException("Exception"); }).build();
 
 listenerCache.put("a", "a");
 listenerCache.put("b", "b"); // causes eviction but should not crash
@@ -161,9 +158,7 @@ void testEvictionListenerExceptionDoesNotCrash() {
 
 @Test
 void testTtlZeroThrowsIllegalArgumentException() {
-Executable exec = () -> new RRCache.Builder<String, String>(3)
-.defaultTTL(-1)
-.build();
+Executable exec = () -> new RRCache.Builder<String, String>(3).defaultTTL(-1).build();
 assertThrows(IllegalArgumentException.class, exec);
 }
 }