refactoring-to-streams

Things to cover

• Converting mutation-and-for-loops and Guava iterables
• Performance
• Parallelising
• Filtering
• Mapping
• Reducing
• Collecting
• Partitioning and grouping
• Generators (infinite streams, streams evaluate lazily)
• Take (re. streams evaluate lazily)
• Flatmap
• Null vs Optional
• ForEach
• Error handling and exceptions