Improved observer pattern documentation with use-case explanation

observer/README.md

@@ -174,6 +174,7 @@ Use the Observer pattern in any of the following situations:
 * When an abstraction has two aspects, one dependent on the other. Encapsulating these aspects in separate objects lets you vary and reuse them independently.
 * When a change to one object requires changing others, and you don't know how many objects need to be changed.
 * When an object should be able to notify other objects without making assumptions about who these objects are. In other words, you don't want these objects tightly coupled.
+* This pattern is especially useful in event-driven systems where changes in one object need to be automatically reflected in multiple dependent objects.
 
 ## Real-World Applications of Observer Pattern in Java
 

singleton/README.md

@@ -78,6 +78,7 @@ Use the Singleton pattern when
 * Configuration classes in many applications
 * Connection pools
 * File manager
+* Database connection management systems to ensure a single shared instance across the application
 * [java.lang.Runtime#getRuntime()](http://docs.oracle.com/javase/8/docs/api/java/lang/Runtime.html#getRuntime%28%29)
 * [java.awt.Desktop#getDesktop()](http://docs.oracle.com/javase/8/docs/api/java/awt/Desktop.html#getDesktop--)
 * [java.lang.System#getSecurityManager()](http://docs.oracle.com/javase/8/docs/api/java/lang/System.html#getSecurityManager--)