BAEL-7145

Bill Pugh Singleton implementation

patterns-modules/design-patterns-singleton/src/main/java/com/baledung/billpugh/BillPughSingleton.java

@@ -0,0 +1,15 @@
+package com.baledung.billpugh;
+
+public class BillPughSingleton {
+    private BillPughSingleton() {
+
+    }
+
+    private static class SingletonHelper {
+        private static final BillPughSingleton BILL_PUGH_SINGLETON_INSTANCE = new BillPughSingleton();
+    }
+
+    public static BillPughSingleton getInstance() {
+        return SingletonHelper.BILL_PUGH_SINGLETON_INSTANCE;
+    }
+}

patterns-modules/design-patterns-singleton/src/main/java/com/baledung/billpugh/EagerLoadedSingleton.java

@@ -0,0 +1,11 @@
+package com.baledung.billpugh;
+
+public class EagerLoadedSingleton {
+    private static final EagerLoadedSingleton EAGER_LOADED_SINGLETON = new EagerLoadedSingleton();
+    private EagerLoadedSingleton() {
+
+    }
+    public static EagerLoadedSingleton getInstance() {
+        return EAGER_LOADED_SINGLETON;
+    }
+}

patterns-modules/design-patterns-singleton/src/main/java/com/baledung/billpugh/LazyLoadedSingleton.java

@@ -0,0 +1,15 @@
+package com.baledung.billpugh;
+
+public class LazyLoadedSingleton {
+    private static LazyLoadedSingleton lazyLoadedSingletonObj;
+
+    private LazyLoadedSingleton() {
+    }
+
+    public static LazyLoadedSingleton getInstance() {
+        if (null == lazyLoadedSingletonObj) {
+            lazyLoadedSingletonObj = new LazyLoadedSingleton();
+        }
+        return lazyLoadedSingletonObj;
+    }
+}

patterns-modules/design-patterns-singleton/src/main/java/com/baledung/billpugh/SynchronizedLazyLoadedSingleton.java

@@ -0,0 +1,15 @@
+package com.baledung.billpugh;
+
+public class SynchronizedLazyLoadedSingleton {
+    private static SynchronizedLazyLoadedSingleton synchronizedLazyLoadedSingleton;
+
+    private SynchronizedLazyLoadedSingleton() {
+    }
+
+    public static synchronized SynchronizedLazyLoadedSingleton getInstance() {
+        if (null == synchronizedLazyLoadedSingleton) {
+            synchronizedLazyLoadedSingleton = new SynchronizedLazyLoadedSingleton();
+        }
+        return synchronizedLazyLoadedSingleton;
+    }
+}