Java 8 in Action: Lambdas, streams, and functional-style programming

Chapter 6. Collecting data with streams

This chapter covers

• Creating and using a collector with the Collectors class
• Reducing streams of data to a single value
• Summarization as a special case of reduction
• Grouping and partitioning data
• Developing your own custom collectors

You learned in the previous chapter that streams help you process collections with database-like operations. You can view Java 8 streams as fancy lazy iterators of sets of data. They support two types of operations: intermediate operations such as filter or map and terminal operations such as count, findFirst, forEach, and reduce. Intermediate operations can be chained to convert a stream into another stream. These operations don’t consume from a stream; their purpose ...