Java8-Stream: 没有类型变量的实例(s)

huangapple
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英文:

Java8-Stream: no instance(s) of type variable(s)

问题

以下是翻译好的内容：

  1. public List<String> getPartnersOfClient(String clientId, MyClient[] allMyClients) {
  3.     Stream<String> myClient =
  4.         Stream.of(allMyClients)
  5.             .filter(client -> client.getId() == Integer.valueOf(clientId))
  6.             .flatMap(client -> Arrays.stream(client.getPartners())
  7.                 .map(partner -> partner.getId()))
  8.             .collect(Collectors.toList());
  9.     return myClient;
  10. }

请注意，翻译中的代码可能需要根据实际情况进行适当的调整。如果有任何问题或需要进一步帮助，请随时提问。

英文:

I have a json as below:

  1. [
  2.     {
  3.         &quot;id&quot;: 2,
  4.         &quot;partners&quot;: [
  5.             {
  6.                 &quot;configuration&quot;: {
  7.                     &quot;connect-fleet-sync&quot;: false
  8.                 },
  9.                 &quot;id&quot;: &quot;cf89cbc5-0886-48cc-81e7-ca6123bc4857&quot;
  10.             },
  11.             {
  12.                 &quot;configuration&quot;: {
  13.                     &quot;connect-fleet-sync&quot;: false
  14.                 },
  15.                 &quot;id&quot;: &quot;cf89cbc5-0886-48cc-81e7-ca6123bc4967&quot;
  16.             }
  17.         ]
  18.     },
  19.     {
  20.         &quot;id&quot;: 3,
  21.         &quot;partners&quot;: [
  22.             {
  23.                 &quot;configuration&quot;: {
  24.                     &quot;connect-fleet-sync&quot;: false
  25.                 },
  26.                 &quot;id&quot;: &quot;c3354af5-16e3-4713-b1f5-a5369c0b13d6&quot;
  27.             }
  28.         ]
  29.     }
  30. ]

I need a method which i receive the id and it gives me ids of partners.

Fr example getPartnersOfClient(2) and then i expect it returns:

  1. [&quot;cf89cbc5-0886-48cc-81e7-ca6123bc4857&quot;,&quot;cf89cbc5-0886-48cc-81e7-ca6123bc4857&quot;]

Here is what i have tried:

  1.   public List&lt;String&gt; getPartnersOfClient(String clientId, MyClient[] allMyClients) {
  3.     Stream&lt;String&gt; myClient =
  4.         Stream.of(allMyClients)
  5.             .filter(client -&gt; client.getId() == Integer.valueOf(clientId))
  6.             .map(MyClient::getPartners)
  7.             .map(Partner::getPartnerId)
  8.             .collect(Collectors.toList());
  9.     return allPartners;
  10.   }

But, in the line .map(Partner::getPartnerId) it complains with:

  1. reason: no instance(s) of type variable(s) exist so that Partner[] conforms to Partner

Here is the picture of error:

Java8-Stream: 没有类型变量的实例(s)

答案1

得分: 1

看起来 getPartners() 返回的是 Partner[]，而不是一个 Partner，因此你不能在这些数组上使用 Partner::getPartnerId。

你可以使用 flatMap 来获得所有单独的 Partner 实例的 Stream<Partner>。

  1. Stream<String> fdeClient =
  2.     Stream.of(allFdeClients)
  3.         .filter(client -> client.getId() == Integer.parseInt(clientId))
  4.         .flatMap(f -> Stream.of(f.getPartners()))
  5.         .map(Partner::getPartnerId)
  6.         .collect(Collectors.toList());
英文:

It looks like getPartners() returns a Partner[], not a Partner, so you can't apply Partner::getPartnerId on these arrays.

You can use flatMap to get a Stream&lt;Partner&gt; of all the individual Partner instances.

  1. Stream&lt;String&gt; fdeClient =
  2.     Stream.of(allFdeClients)
  3.         .filter(client -&gt; client.getId() == Integer.parseInt(clientId))
  4.         .flatMap(f -&gt; Stream.of(f.getPartners()))
  5.         .map(Partner::getPartnerId)
  6.         .collect(Collectors.toList());

huangapple
  • 本文由 发表于 2020年10月15日 17:08:09
  • 转载请务必保留本文链接：https://go.coder-hub.com/64368272.html
  • java
  • java-8
  • java-stream
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