为什么这段代码用jdk8u45及以上版本编译但不用jdk8u25编译？ [英] Why this code compiles with jdk8u45 and above but not with jdk8u25?

问题描述

拜托，有人可以帮我弄清楚为什么下面的代码用jdk8u45及以上代码编译但是jdk8u25失败了吗？
我查看了JDK发行说明，但没有找到任何与此问题相关的内容或者可能错过了它。

Please, could someone help me to figure out why the following code compiles with jdk8u45 and above but fails with jdk8u25? I looked through the JDK release notes but didn't find anything related to the issue or maybe missed it.

代码

public class Main {

    static class Param {
        final int id;

        Param(int id) {
            this.id = id;
        }
    }

    static class Subtask {
        final Param param;

        Subtask(Param param) {
            this.param = param;
        }
    }

    public static void main(String[] args) {
        List<? extends Param> params = IntStream.range(1, 100).mapToObj(Param::new).collect(Collectors.toList());
        NavigableMap<String, Subtask> map = params.stream()
                .collect(Collectors.toMap(p -> UUID.randomUUID().toString(), Subtask::new, (a, b) -> a, TreeMap::new));
    }
}

jdk8u25例外：

jdk8u25 exception:

Error:(33, 17) java: no suitable method found for collect(java.util.stream.Collector<org.ka.Main.Param,capture#1 of ?,java.util.TreeMap<java.lang.String,org.ka.Main.Subtask>>)
    method java.util.stream.Stream.<R>collect(java.util.function.Supplier<R>,java.util.function.BiConsumer<R,? super capture#2 of ? extends org.ka.Main.Param>,java.util.function.BiConsumer<R,R>) is not applicable
      (cannot infer type-variable(s) R
        (actual and formal argument lists differ in length))
    method java.util.stream.Stream.<R,A>collect(java.util.stream.Collector<? super capture#2 of ? extends org.ka.Main.Param,A,R>) is not applicable
      (cannot infer type-variable(s) R,A,capture#3 of ?,T,K,U,M,K,V
        (argument mismatch; java.util.stream.Collector<capture#2 of ? extends org.ka.Main.Param,capture#4 of ?,java.util.TreeMap<java.lang.Object,org.ka.Main.Subtask>> cannot be converted to java.util.stream.Collector<? super capture#2 of ? extends org.ka.Main.Param,capture#4 of ?,java.util.TreeMap<java.lang.Object,org.ka.Main.Subtask>>))

推荐答案

我在8u5到8u25之间的类型推理遇到了类似问题，并在8u40中得到修复。 8u40中的错误修复列表有一些javac修复与嵌套的lambda身体错误地排除了一些重载决议的方法，我认为你的问题是。

I had similar problems with type inferencing which broke somewhere between 8u5 and 8u25 and was fixed in 8u40. The bug fix list in 8u40 has some javac fixes having to do with nested lambda bodies incorrectly ruling out some methods in overload resolution which is what I think your problem is.

这是 8u40中的所有错误修复

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