Java 8嵌套lambdas中断编译器

Question

我对Java 8有一个复杂的问题。

问题

与嵌套的lambda编译器一起崩溃NullPointerException！

我知道lambda必须确实是无状态的，在这种情况下，具有状态的代码是Supplier实现，但它们是匿名类而不是lambda。

码

import java.util.function.Function;
import java.util.function.Supplier;

public class Test {

    public static Function<String, Supplier<String>> A = aVal -> new Supplier<String>() {

        @Override
        public String get() {
            return B.apply(aVal).get();
        }

        private Function<String, Supplier<String>> B = bVal -> new Supplier<String>() {
            @Override
            public String get() {
                return C.apply(bVal).get();
            }

            private Function<String, Supplier<String>> C = cVal -> new Supplier<String>() {
                @Override
                public String get() {
                    return cVal;
                }
            };
        };
    };
}

堆栈跟踪

An exception has occurred in the compiler (1.8.0_211). Please file a bug against the Java compiler via the Java bug reporting page (http://bugrepor
t.java.com) after checking the Bug Database (http://bugs.java.com) for duplicates. Include your program and the following diagnostic in your report
. Thank you.
java.lang.NullPointerException
        at com.sun.tools.javac.jvm.Code.emitop0(Code.java:559)
        at com.sun.tools.javac.jvm.Items$SelfItem.load(Items.java:367)
        at com.sun.tools.javac.jvm.Gen.genArgs(Gen.java:966)
        at com.sun.tools.javac.jvm.Gen.visitApply(Gen.java:1842)
        at com.sun.tools.javac.tree.JCTree$JCMethodInvocation.accept(JCTree.java:1465)
        at com.sun.tools.javac.jvm.Gen.genExpr(Gen.java:947)
        at com.sun.tools.javac.jvm.Gen.visitAssign(Gen.java:1982)
        at com.sun.tools.javac.tree.JCTree$JCAssign.accept(JCTree.java:1686)
        at com.sun.tools.javac.jvm.Gen.genExpr(Gen.java:947)
        at com.sun.tools.javac.jvm.Gen.visitExec(Gen.java:1781)
        at com.sun.tools.javac.tree.JCTree$JCExpressionStatement.accept(JCTree.java:1296)
        at com.sun.tools.javac.jvm.Gen.genDef(Gen.java:737)
        at com.sun.tools.javac.jvm.Gen.genStat(Gen.java:772)
        at com.sun.tools.javac.jvm.Gen.genStat(Gen.java:758)
        at com.sun.tools.javac.jvm.Gen.genStats(Gen.java:809)
        at com.sun.tools.javac.jvm.Gen.visitBlock(Gen.java:1157)
        at com.sun.tools.javac.tree.JCTree$JCBlock.accept(JCTree.java:909)
        at com.sun.tools.javac.jvm.Gen.genDef(Gen.java:737)
        at com.sun.tools.javac.jvm.Gen.genStat(Gen.java:772)
        at com.sun.tools.javac.jvm.Gen.genMethod(Gen.java:1031)
        at com.sun.tools.javac.jvm.Gen.visitMethodDef(Gen.java:994)
        at com.sun.tools.javac.tree.JCTree$JCMethodDecl.accept(JCTree.java:778)
        at com.sun.tools.javac.jvm.Gen.genDef(Gen.java:737)
        at com.sun.tools.javac.jvm.Gen.genClass(Gen.java:2454)
        at com.sun.tools.javac.main.JavaCompiler.genCode(JavaCompiler.java:745)
        at com.sun.tools.javac.main.JavaCompiler.generate(JavaCompiler.java:1572)
        at com.sun.tools.javac.main.JavaCompiler.generate(JavaCompiler.java:1536)
        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.api.JavacTaskImpl.doCall(JavacTaskImpl.java:129)
        at com.sun.tools.javac.api.JavacTaskImpl.call(JavacTaskImpl.java:138)
        at org.codehaus.plexus.compiler.javac.JavaxToolsCompiler.compileInProcess(JavaxToolsCompiler.java:125)
        at org.codehaus.plexus.compiler.javac.JavacCompiler.performCompile(JavacCompiler.java:171)
        at org.apache.maven.plugin.compiler.AbstractCompilerMojo.execute(AbstractCompilerMojo.java:886)
        at org.apache.maven.plugin.compiler.CompilerMojo.execute(CompilerMojo.java:129)
        at org.apache.maven.plugin.DefaultBuildPluginManager.executeMojo(DefaultBuildPluginManager.java:134)
        at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:208)
        at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:154)
        at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:146)
        at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject(LifecycleModuleBuilder.java:117)
        at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject(LifecycleModuleBuilder.java:81)
        at org.apache.maven.lifecycle.internal.builder.singlethreaded.SingleThreadedBuilder.build(SingleThreadedBuilder.java:51)
        at org.apache.maven.lifecycle.internal.LifecycleStarter.execute(LifecycleStarter.java:128)
        at org.apache.maven.DefaultMaven.doExecute(DefaultMaven.java:309)
        at org.apache.maven.DefaultMaven.doExecute(DefaultMaven.java:194)
        at org.apache.maven.DefaultMaven.execute(DefaultMaven.java:107)
        at org.apache.maven.cli.MavenCli.execute(MavenCli.java:955)
        at org.apache.maven.cli.MavenCli.doMain(MavenCli.java:290)
        at org.apache.maven.cli.MavenCli.main(MavenCli.java:194)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.lang.reflect.Method.invoke(Method.java:498)
        at org.codehaus.plexus.classworlds.launcher.Launcher.launchEnhanced(Launcher.java:289)
        at org.codehaus.plexus.classworlds.launcher.Launcher.launch(Launcher.java:229)
        at org.codehaus.plexus.classworlds.launcher.Launcher.mainWithExitCode(Launcher.java:415)
        at org.codehaus.plexus.classworlds.launcher.Launcher.main(Launcher.java:356)

---

测验

我在不同的版本（1.8.111、1.8.152、1.8.162、1.8.211）和不同的环境（Windows，Mac）上进行了几次尝试。

我尝试使用CMD mvn clean compile或通过使用maven插件的intelliJ进行尝试。

删除功能C都可以正常工作。

---

我的猜想

假设1 这是Java 8的限制，IntelliJ有一个错误，尽管Java 8无法处理，但我可以将匿名类折叠为lambda。

假设2 这是Java 8错误。

对于这个有趣的Java问题，我需要您的帮助。谢谢 ：）

---

更新

我已经在Java Bug Database上打开了一个bug。我确认这是一个错误，并且已在更高版本9、10、11等上解决。

https://bugs.java.com/bugdatabase/view_bug.do?bug_id=JDK-8225771

Answer 1

这是Java编译器的错误¹。我可以使用从命令行运行的javac版本来重现它1.8.0_212。（没有使用或损坏任何IDE。）

该错误在javacversion中不存在10.0.1，因此将工具链升级到Java 11将解决此问题。

^{1-导致编译器因NPE崩溃的任何问题都是bug！}