Collectorsreducing求和返回对象

The collectors.reducing method in Java is used to reduce the elements of a stream to a single value. It takes three parameters: an initial value, an accumulator function, and an optional finisher function.

The reducing collector returns an object that represents the reduction operation. This object can be further processed or used to obtain the final result.

Here is an example of using the reducing collector to find the sum of a list of integers:

List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5);

int sum = numbers.stream()
                .collect(Collectors.reducing(0, (a, b) -> a + b));

System.out.println(sum); // Output: 15

In this example, the reducing collector starts with an initial value of 0 and uses the lambda expression (a, b) -> a + b as the accumulator function. The accumulator function takes two parameters, a and b, and returns their sum. The collector applies this function to each element of the stream, accumulating the sum.

The resulting object returned by the reducing collector represents the sum of all the elements in the stream. In this case, the final result is obtained by calling the get() method on the object.

Note that the reducing collector can also take an optional finisher function to perform additional operations on the result. However, in this example, we did not provide a finisher function, so the result is directly returned as an Integer