将foreach转换为filter

huangapple
go评论101阅读模式
英文:

converting foreach to filter

问题

我想将代码从这样：

  1. List<FlightPositionRoute> flightPositionRoutes = new ArrayList<>();
  3. dtos.stream()
  4.     .map(a -> positions.getPositions(a.getId().getValue()))
  5.     .forEach(flightPositionRoute -> flightPositionRoute.ifPresent(flightPositionRoutes::add));

转换为这样：

  1. List<FlightPositionRoute> flightPositionRoutes = dtos.stream()
  2.     .map(a -> positions.getPositions(a.getId().getValue()))
  3.     .filter(Optional::isPresent)
  4.     .map(Optional::get)
  5.     .collect(Collectors.toList());

我的意思是，我想使用 filter 代替 foreach，因为它更优雅 将foreach转换为filter

不过，很遗憾，我遇到了这个问题：

  1. Required type: List<FlightPositionRoute>
  2. Provided: List<Optional<FlightPositionRoute>>
  3. 如何修复这个问题？
英文:

I would like to convert

  1. List&lt;FlightPositionRoute&gt; flightPositionRoutes = new ArrayList&lt;&gt;();
  3.             dtos.stream()
  4.                     .map(a-&gt; positions.getPositions(a.getId()
  5.                             .getValue()))
  6.                     .forEach(flightPositionRoute -&gt; 
  7.                                flightPositionRoute.ifPresent(flightPositionRoutes::add));

To this:

  1. List&lt;FlightPositionRoute&gt; flightPositionRoutes = dtos.stream()
  2.                     .map(a-&gt; positions.getPositions(a.getId()
  3.                             .getValue()))
  4.                     .filter(Optional::isPresent)
  5.                     .collect(Collectors.toList());

I mean I would like to use filter instead of foreach, because it's prettier 将foreach转换为filter

Unfortunately, I'm getting

  1. Required type: List &lt;FlightPositionRoute&gt;
  2. Provided: List &lt;Optional&lt;FlightPositionRoute&gt;&gt;

How can I repair it?

答案1

得分: 2

你只需要解开 Optional：

  1. List<FlightPositionRoute> flightPositionRoutes = dtos.stream()
  2.     .map(a -> positions.getPositions(a.getId().getValue()))
  3.     .filter(Optional::isPresent)
  4.     .map(Optional::get)
  5.     .collect(Collectors.toList());
英文:

You just need to unpack the Optional:

  1. List&lt;FlightPositionRoute&gt; flightPositionRoutes = dtos.stream()
  2.     .map(a-&gt; positions.getPositions(a.getId().getValue()))
  3.     .filter(Optional::isPresent)
  4.     .map(Optional::get)
  5.     .collect(Collectors.toList());

huangapple
  • 本文由 发表于 2020年10月8日 02:13:45
  • 转载请务必保留本文链接：https://go.coder-hub.com/64249992.html
  • java
  • java-stream
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