add double check lock Singleton

dynamicy · dynamicy · commit 012da331818f · 2014-11-12T01:02:08.000+08:00
diff --git a/SingletonPattern/Java/DoubleCheckLockSingleton.java b/SingletonPattern/Java/DoubleCheckLockSingleton.java
@@ -0,0 +1,26 @@
+public class DoubleCheckLockSingleton
+{
+    private static DoubleCheckLockSingleton instance = null;
+
+    // Make this instance can be accessed only by public method
+    private DoubleCheckLockSingleton()
+    {
+    }
+
+    public static DoubleCheckLockSingleton getInstance() 
+    {
+        // Only if it's the first for creating instance
+        if (instance == null)
+        {
+            // The method is synchronized on the class object
+            synchronized(DoubleCheckLockSingleton.class)
+            {
+                if(instance == null) 
+                {
+                    instance = new DoubleCheckLockSingleton();
+                }
+            }
+        }
+        return instance;
+    }
+}
