Java Stream 和 reduce 的 8 个编译器错误

Question

我正在编写一个小程序来生成一些随机数，并希望获得有关它们的统计信息。我有一个 List<AtomicInteger> 想用来输出一些信息。

我尝试使用以下代码将列表减少到总数（例如，所有 AtomicIntegers 的值的总和）：

// not my real initialization code, just for illustration purposes
List<AtomicInteger> values = new ArrayList<>();
for(int i = 0; i < 10; i++) {
    values.add(new AtomicInteger());
}

// this is the problematic reduce
int total = values
    .parallelStream()
    .reduce(0, 
        (currentValue, currentAtomic) 
            -> currentValue + currentAtomic.get(),
        (combiner1, combiner2) -> combiner1 + combiner2);

我的 IDE (IntelliJ) 对此行没有任何问题，但对于我当前的 javac 版本 (1.8.0_31)，此行在编译器中导致 NullPointerException :

An exception has occurred in the compiler (1.8.0_31). Please file a bug at the Java Developer Connection (http://java.sun.com/webapps/bugreport)  after checking the Bug Parade for duplicates. Include your program and the following diagnostic in your report.  Thank you.
java.lang.NullPointerException
    at com.sun.tools.javac.code.Types.isConvertible(Types.java:290)
    at com.sun.tools.javac.comp.Check.assertConvertible(Check.java:922)
    at com.sun.tools.javac.comp.Check.checkMethod(Check.java:876)
    at com.sun.tools.javac.comp.Attr.checkMethod(Attr.java:3838)
    at com.sun.tools.javac.comp.Attr.checkIdInternal(Attr.java:3615)
    at com.sun.tools.javac.comp.Attr.checkMethodIdInternal(Attr.java:3522)
    at com.sun.tools.javac.comp.Attr.checkMethodId(Attr.java:3501)
    at com.sun.tools.javac.comp.Attr.checkId(Attr.java:3488)
    at com.sun.tools.javac.comp.Attr.visitSelect(Attr.java:3370)
    at com.sun.tools.javac.tree.JCTree$JCFieldAccess.accept(JCTree.java:1897)
    at com.sun.tools.javac.comp.Attr.attribTree(Attr.java:607)
    at com.sun.tools.javac.comp.Attr.visitApply(Attr.java:1843)
    at com.sun.tools.javac.tree.JCTree$JCMethodInvocation.accept(JCTree.java:1465)
    at com.sun.tools.javac.comp.Attr.attribTree(Attr.java:607)
    at com.sun.tools.javac.comp.Attr.attribExpr(Attr.java:649)
    at com.sun.tools.javac.comp.Attr.visitVarDef(Attr.java:1093)
    at com.sun.tools.javac.tree.JCTree$JCVariableDecl.accept(JCTree.java:852)
    at com.sun.tools.javac.comp.Attr.attribTree(Attr.java:607)
    at com.sun.tools.javac.comp.Attr.attribStat(Attr.java:676)
    at com.sun.tools.javac.comp.Attr.attribStats(Attr.java:692)
    at com.sun.tools.javac.comp.Attr.visitBlock(Attr.java:1142)
    at com.sun.tools.javac.tree.JCTree$JCBlock.accept(JCTree.java:909)
    at com.sun.tools.javac.comp.Attr.attribTree(Attr.java:607)
    at com.sun.tools.javac.comp.Attr.attribStat(Attr.java:676)
    at com.sun.tools.javac.comp.Attr.visitMethodDef(Attr.java:1035)
    at com.sun.tools.javac.tree.JCTree$JCMethodDecl.accept(JCTree.java:778)
    at com.sun.tools.javac.comp.Attr.attribTree(Attr.java:607)
    at com.sun.tools.javac.comp.Attr.attribStat(Attr.java:676)
    at com.sun.tools.javac.comp.Attr.attribClassBody(Attr.java:4342)
    at com.sun.tools.javac.comp.Attr.attribClass(Attr.java:4252)
    at com.sun.tools.javac.comp.Attr.attribClass(Attr.java:4181)
    at com.sun.tools.javac.comp.Attr.attrib(Attr.java:4156)
    at com.sun.tools.javac.main.JavaCompiler.attribute(JavaCompiler.java:1248)
    at com.sun.tools.javac.main.JavaCompiler.compile2(JavaCompiler.java:901)
    at com.sun.tools.javac.main.JavaCompiler.compile(JavaCompiler.java:860)
    at com.sun.tools.javac.main.Main.compile(Main.java:523)
    at com.sun.tools.javac.main.Main.compile(Main.java:381)
    at com.sun.tools.javac.main.Main.compile(Main.java:370)
    at com.sun.tools.javac.main.Main.compile(Main.java:361)
    at com.sun.tools.javac.Main.compile(Main.java:56)
    at com.sun.tools.javac.Main.main(Main.java:42)

我知道可能还有其他方法可以完成相同的 reduce，但我真的很想保留流的并行性质（因为我的原始代码有很多值）。任何人都可以向我推荐另一个不会使我的编译器崩溃并且可以实现相同结果的并行 reduce 选项吗？

我还想知道这是否只是我遇到的问题，或者其他人是否可以重现此编译器错误。

Answer 1

不会使编译器崩溃的版本：

// not my real initialization code, just for illustration purposes
        List<AtomicInteger> values = new ArrayList<>();
        for(int i = 0; i < 10; i++) {
            values.add(new AtomicInteger());
        }

// this is the problematic reduce
        BiFunction<Integer, AtomicInteger, Integer> accumulator = 
                (currentValue, currentAtomic) -> currentValue + currentAtomic.get();
        BinaryOperator<Integer> combiner = (combiner1, combiner2) -> combiner1 + combiner2;
        int total = values
                .parallelStream()
                .reduce(0, accumulator, combiner);

Answer 2

或者，除了使用 reduce，您还可以使用 mapToInt 和 sum：

int total = values.stream().mapToInt(AtomicInteger::get).sum();

Java Stream 和 reduce 的 8 个编译器错误

Java 8 compiler bug with Stream and reduce

java

java-8