Merge branch 'tomekl007-HEXA-672'

core-java/pom.xml

@@ -154,6 +154,12 @@
             <version>${mockito.version}</version>
             <scope>test</scope>
         </dependency>
+        <dependency>
+            <groupId>com.jayway.awaitility</groupId>
+            <artifactId>awaitility</artifactId>
+            <version>${avaitility.version}</version>
+            <scope>test</scope>
+        </dependency>
 
         <dependency>
             <groupId>commons-codec</groupId>
@@ -371,6 +377,7 @@
         <mockito.version>1.10.19</mockito.version>
         <testng.version>6.10</testng.version>
         <assertj.version>3.6.1</assertj.version>
+        <avaitility.version>1.7.0</avaitility.version>
 
         <!-- maven plugins -->
         <maven-compiler-plugin.version>3.6.0</maven-compiler-plugin.version>

core-java/src/test/java/com/baeldung/weakhashmap/WeakHashMapTest.java

@@ -0,0 +1,72 @@
+package com.baeldung.weakhashmap;
+
+
+import org.junit.Test;
+
+import java.util.WeakHashMap;
+import java.util.concurrent.TimeUnit;
+
+import static com.jayway.awaitility.Awaitility.await;
+import static org.junit.Assert.assertTrue;
+
+public class WeakHashMapTest {
+
+    @Test
+    public void givenWeakHashMap_whenCacheValueThatHasNoReferenceToIt_GCShouldReclaimThatObject() {
+        //given
+        WeakHashMap<UniqueImageName, BigImage> map = new WeakHashMap<>();
+        BigImage bigImage = new BigImage("image_id");
+        UniqueImageName imageName = new UniqueImageName("name_of_big_image");
+
+        map.put(imageName, bigImage);
+        assertTrue(map.containsKey(imageName));
+
+        //when big image key is not reference anywhere
+        imageName = null;
+        System.gc();
+
+        //then GC will finally reclaim that object
+        await().atMost(10, TimeUnit.SECONDS).until(map::isEmpty);
+    }
+
+    @Test
+    public void givenWeakHashMap_whenCacheValueThatHasNoReferenceToIt_GCShouldReclaimThatObjectButLeaveReferencedObject() {
+        //given
+        WeakHashMap<UniqueImageName, BigImage> map = new WeakHashMap<>();
+        BigImage bigImageFirst = new BigImage("foo");
+        UniqueImageName imageNameFirst = new UniqueImageName("name_of_big_image");
+
+        BigImage bigImageSecond = new BigImage("foo_2");
+        UniqueImageName imageNameSecond = new UniqueImageName("name_of_big_image_2");
+
+        map.put(imageNameFirst, bigImageFirst);
+        map.put(imageNameSecond, bigImageSecond);
+        assertTrue(map.containsKey(imageNameFirst));
+        assertTrue(map.containsKey(imageNameSecond));
+
+        //when
+        imageNameFirst = null;
+        System.gc();
+
+        //then
+        await().atMost(10, TimeUnit.SECONDS).until(() -> map.size() == 1);
+        await().atMost(10, TimeUnit.SECONDS).until(() -> map.containsKey(imageNameSecond));
+    }
+
+
+    class BigImage {
+        public final String imageId;
+
+        BigImage(String imageId) {
+            this.imageId = imageId;
+        }
+    }
+
+    class UniqueImageName {
+        public final String imageName;
+
+        UniqueImageName(String imageName) {
+            this.imageName = imageName;
+        }
+    }
+}