我在Java 8方面遇到了一个复杂的问题。
问题
使用嵌套Lambda表达式时，编译器会崩溃并出现 NullPointerException!
我知道Lambda必须是无状态的。但在这种情况下，具有状态的代码是实现Supplier接口的匿名类而不是Lambda表达式。
代码
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)
测试
我尝试了不同版本(1.8.111, 1.8.152, 1.8.162, 1.8.211)和不同环境（Windows，Mac）多次尝试。
我使用命令行工具CMD或通过IntelliJ使用Maven插件mvn clean compile尝试。
删除C函数后，所有内容都能正常运行。
我的假设
假设1 这是Java 8的限制，而IntelliJ有一个错误，允许我将匿名类折叠成lambda表达式，尽管java 8无法处理它们。
假设2 这是Java 8的bug。
我请求你的帮助来解决这个有趣的Java问题。 谢谢 :)
更新
我已经在Java Bug Database上开了一个bug。我确认这是一个bug，并且已经在更高版本9，10，11等中得到了解决...
https://bugs.java.com/bugdatabase/view_bug.do?bug_id=JDK-8225771
javac不应该崩溃。 - Sean Bright