Streams - Java 8 Lambdas - page 31

assertEquals ( 6 , count );

The lambda expression returns the new acc value, which is the previous acc added to the
current element. The type of the reducer is a BinaryOperator , which we encountered in
Chapter 2 .

NOTE

Primitives also refers to an implementation of sum within the standard library, which is re-
commended instead of the approach shown in this example in real code.

Table 3-1 shows the intermediate values for these variables for each element in the Stream .
In fact, we could expand all the function applications that reduce to produce the code in
Example 3-17 .

Example 3-17. Expanding the application of reduce
BinaryOperator < Integer > accumulator = ( acc , element ) -> acc + element ;
int

int count = accumulator . apply (
accumulator . apply (
accumulator . apply ( 0 , 1 ),

2 ),

3 );

Table 3-1. Evaluating a sum reduce

element acc Result

N/A N/A 0

1 0 1

2 1 3

3 3 6

Let's look at the equivalent imperative Java code, written in Example 3-18 , so we can see
how the functional and imperative versions match up.