[Java] Use Collectors.collectingAndThen

What is Collectors.collectingAndThen?

A Collector that returns the processed value after the Collect.

How to use

Suppose you have the following situation:

Temporarily store in list → call process

List<Integer> mappedList = /* Stream */
    ./*Stream processing such as map*/

return hogeFunc(mappedList);

Such processing can be written as follows by using Collectors.collectingAndThen.

Collectors.Form using collectingAndThen

return /* Stream */
  ./*Stream processing such as map*/
          mappedList -> hogeFunc(mappedList) //Processing using mappedList

What are you happy about?

Temporary variables decrease

Since it is not necessary to store the Collect results in temporary variables one by one, the number of temporary variables can be reduced. Putting a temporary variable leads to poor readability and code quality, so I'm happy to reduce it.

Readability is higher than direct delivery

The code example given at the beginning can also be written as:

When written in the form of passing arguments directly to the function

return hogeFunc(
    /* Stream */
        ./*Stream processing such as map*/

However, this is [^ hosoku], which is less readable, especially when functions are nested. In addition, this has the disadvantage that it cannot be read by hooking it with the debugger.

[^ hosoku]: For this scene, if you have a pipeline operator, you don't even need to use Collectors.collectingAndThen ...


Let's use Collectors.collectingAndThen.

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