all index.md files renamed to README.md for more compatibility with github

double-dispatch/README.md

@@ -0,0 +1,26 @@
+---
+layout: pattern
+title: Double Dispatch
+folder: double-dispatch
+permalink: /patterns/double-dispatch/
+categories: Other
+tags:
+ - Java
+ - Difficulty-Intermediate
+ - Idiom
+---
+
+## Intent
+Double Dispatch pattern is a way to create maintainable dynamic
+behavior based on receiver and parameter types.
+
+![alt text](./etc/double-dispatch.png "Double Dispatch")
+
+## Applicability
+Use the Double Dispatch pattern when
+
+* the dynamic behavior is not defined only based on receiving object's type but also on the receiving method's parameter type.
+
+## Real world examples
+
+* [ObjectOutputStream](https://docs.oracle.com/javase/8/docs/api/java/io/ObjectOutputStream.html)