Java 8 Streams - collect vs reduce

Question

When would you use collect() vs reduce()? Does anyone have good, concrete examples of when it\'s definitely better to go one way or the other?

Answer 1

Here is the code example

List list = Arrays.asList(1,2,3,4,5,6,7);
int sum = list.stream().reduce((x,y) -> {
        System.out.println(String.format("x=%d,y=%d",x,y));
        return (x + y);
    }).get();

System.out.println(sum);

Here is the execute result:

x=1,y=2
x=3,y=3
x=6,y=4
x=10,y=5
x=15,y=6
x=21,y=7
28

Reduce function handle two parameters, the first parameter is the previous return value int the stream, the second parameter is the current calculate value in the stream, it sum the first value and current value as the first value in next caculation.