Refactor awaitility (#2226)

* Awaitility refactor

* Refactor

libraries/src/main/java/com/baeldung/awaitility/AsyncService.java

@@ -8,25 +8,23 @@ public class AsyncService {
     private final int DELAY = 1000;
     private final int INIT_DELAY = 2000;
 
-    private AtomicLong value = new AtomicLong(0);
-    private Executor executor = Executors.newFixedThreadPool(4);
+    private final AtomicLong value = new AtomicLong(0);
+    private final Executor executor = Executors.newFixedThreadPool(4);
     private volatile boolean initialized = false;
 
-    public void initialize() {
+    void initialize() {
         executor.execute(() -> {
             sleep(INIT_DELAY);
             initialized = true;
         });
     }
 
-    public boolean isInitialized() {
+    boolean isInitialized() {
         return initialized;
     }
 
-    public void addValue(long val) {
-        if (!isInitialized()) {
-            throw new IllegalStateException("Service is not initialized");
-        }
+    void addValue(long val) {
+        throwIfNotInitialized();
         executor.execute(() -> {
             sleep(DELAY);
             value.addAndGet(val);
@@ -34,9 +32,7 @@ public class AsyncService {
     }
 
     public long getValue() {
-        if (!isInitialized()) {
-            throw new IllegalStateException("Service is not initialized");
-        }
+        throwIfNotInitialized();
         return value.longValue();
     }
 
@@ -47,4 +43,10 @@ public class AsyncService {
             e.printStackTrace();
         }
     }
+
+    private void throwIfNotInitialized() {
+        if (!initialized) {
+            throw new IllegalStateException("Service is not initialized");
+        }
+    }
 }