Updated Java 8 Stream examples in GS Collections Kata

[Raab, Donald]

I updated the Java 8 Lambda version of our GS Collections Kata.  I used the latest version of the Java 8 Lambda binary (November).

Updated tests are here:
https://github.com/goldmansachs/gs-collections-kata/tree/solutions-java8-jcf/src/test/java/com/gs/collections/kata

Updated domain is here:
https://github.com/goldmansachs/gs-collections-kata/tree/solutions-java8-jcf/src/main/java/com/gs/collections/kata

The things I found awkward using in the kata were flatMap and Optional in the null case.  Examples of both are as follows in the Company domain class:

https://github.com/goldmansachs/gs-collections-kata/blob/solutions-java8-jcf/src/main/java/com/gs/collections/kata/Company.java

Compare with GS Collections flatCollect and detect in this example.

https://github.com/goldmansachs/gs-collections-kata/blob/solutions-java8/src/main/java/com/gs/collections/kata/Company.java

You'll note the need to cast null to Customer in the orElse case due to the overloaded method taking a Factory.

I found flatMap unintuitive and I now understand the confusion it was causing.  Here are two more examples in Exercise 4 and Exercise 9.  Compare the findItemNames (Ex4) mostExpensiveItem (Ex9) tests between Java 8 Streams and GS Collections with Lambdas.

Java 8 flatMap
https://github.com/goldmansachs/gs-collections-kata/blob/solutions-java8-jcf/src/test/java/com/gs/collections/kata/Exercise4Test.java
https://github.com/goldmansachs/gs-collections-kata/blob/solutions-java8-jcf/src/test/java/com/gs/collections/kata/Exercise9Test.java

GS Collections flatCollect
https://github.com/goldmansachs/gs-collections-kata/blob/solutions-java8/src/test/java/com/gs/collections/kata/Exercise4Test.java
https://github.com/goldmansachs/gs-collections-kata/blob/solutions-java8/src/test/java/com/gs/collections/kata/Exercise9Test.java

It would be much nicer to have a form of flatMap that allows for using a method reference IMO.  This will be a very common use case, especially in cases where there is an object graph with one-to-many relationships.








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