BAEL-4464 : how to implement LRU-Cache in java codes added (#11036)

* BAEL-4464 : how to implement LRU-Cache in java codes added

* BAEL-4464 : how to implement LRU-Cache in java codes added - package named fixed

* BAEL-4464 : how to implement LRU-Cache in java codes added - package named changed

* BAEL-4464 : how to implement LRU-Cache in java codes added - unitTest fixed

data-structures/src/test/java/com/baeldung/lrucache/LRUCacheUnitTest.java

@@ -0,0 +1,59 @@
+package com.baeldung.lrucache;
+
+import com.baeldung.lrucache.Cache;
+import com.baeldung.lrucache.LRUCache;
+import org.hamcrest.core.AllOf;
+import org.junit.Before;
+import org.junit.Test;
+import java.util.*;
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.stream.IntStream;
+
+import static org.hamcrest.core.Is.is;
+import static org.junit.Assert.*;
+
+public class LRUCacheUnitTest {
+
+    @Test
+    public void addSomeDataToCache_WhenGetData_ThenIsEqualWithCacheElement() {
+        LRUCache<String, String> lruCache = new LRUCache<>(3);
+        lruCache.put("1", "test1");
+        lruCache.put("2", "test2");
+        lruCache.put("3", "test3");
+        assertEquals(lruCache.get("1").get(), "test1");
+        assertEquals(lruCache.get("2").get(), "test2");
+        assertEquals(lruCache.get("3").get(), "test3");
+    }
+
+    @Test
+    public void addDataToCacheToTheNumberOfSize_WhenAddOneMoreData_ThenLeastRecentlyDataWillEvict() {
+        LRUCache<String, String> lruCache = new LRUCache<>(3);
+        lruCache.put("1", "test1");
+        lruCache.put("2", "test2");
+        lruCache.put("3", "test3");
+        lruCache.put("4", "test4");
+        assertEquals(lruCache.get("1").isPresent(), false);
+    }
+
+    @Test
+    public void runMultiThreadTask_WhenPutDataInConcurrentToCache_ThenNoDataLost() throws Exception {
+        final int size = 50;
+        final ExecutorService executorService = Executors.newFixedThreadPool(5);
+        Cache<Integer, String> cache = new LRUCache<>(size);
+        CountDownLatch countDownLatch = new CountDownLatch(size);
+        try {
+            IntStream.range(0, size).<Runnable>mapToObj(key -> () -> {
+                cache.put(key, "value" + key);
+                System.out.println(Thread.currentThread().getName() + " " + key);
+                countDownLatch.countDown();
+            }).forEach(executorService::submit);
+            countDownLatch.await();
+        } finally {
+            executorService.shutdown();
+        }
+        assertEquals(cache.size(), size);
+        IntStream.range(0, size).forEach(i -> assertEquals(cache.get(i).get(), "value" + i));
+    }
+}