//The following example describes the following pipeline of operations, which 
//calculates the average age of all male members in the collection roster:

double average = roster
    .filter(p -> p.getGender() == Person.Sex.MALE)

The JDK contains many terminal operations (such as average, sum, min, max, and count) that return one value by combining the contents of a stream. These operations are called reduction operations.

The JDK also contains reduction operations that return a collection instead of a single value. Many reduction operations perform a specific task, such as finding the average of values or grouping elements into categories.

Reduction — Structure map

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Reduction — Related pages: