我的 Java 编译器有问题。我将我的代码简化为:

package a;

public class Base {
  // compiles if this is made public or an int
  protected Integer value = 0;
}

---

package b; // must be in a separate package

import a.Base;

public class Sub extends Base {
  public void increment() {
    System.out.println(super.value);
    value++;
    super.value = 1;
    super.value = super.value + 1;
    // this line crashes the compiler; the others all work
    super.value++;
  }
}

编译后我得到:

Information:java: An exception has occurred in the compiler (1.8.0_51). 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.
Information:java: java.lang.NullPointerException
Information:java:   at com.sun.tools.javac.code.Symbol$ClassSymbol.isSubClass(Symbol.java:1020)
Information:java:   at com.sun.tools.javac.comp.Lower.accessClass(Lower.java:1108)
Information:java:   at com.sun.tools.javac.comp.Lower.accessSymbol(Lower.java:983)
Information:java:   at com.sun.tools.javac.comp.Lower.access(Lower.java:1220)
Information:java:   at com.sun.tools.javac.comp.Lower.visitSelect(Lower.java:3855)
Information:java:   at com.sun.tools.javac.tree.JCTree$JCFieldAccess.accept(JCTree.java:1897)
Information:java:   at com.sun.tools.javac.tree.TreeTranslator.translate(TreeTranslator.java:58)
Information:java:   at com.sun.tools.javac.comp.Lower.translate(Lower.java:2371)
Information:java:   at com.sun.tools.javac.comp.Lower.translate(Lower.java:2382)
Information:java:   at com.sun.tools.javac.comp.Lower.visitVarDef(Lower.java:3547)
Information:java:   at com.sun.tools.javac.tree.JCTree$JCVariableDecl.accept(JCTree.java:852)
Information:java:   at com.sun.tools.javac.tree.TreeTranslator.translateVarDefs(TreeTranslator.java:78)
Information:java:   at com.sun.tools.javac.comp.Lower.visitLetExpr(Lower.java:3859)
Information:java:   at com.sun.tools.javac.tree.JCTree$LetExpr.accept(JCTree.java:2426)
Information:java:   at com.sun.tools.javac.comp.Lower.visitLetExpr(Lower.java:3860)
Information:java:   at com.sun.tools.javac.comp.Lower.visitUnary(Lower.java:3319)
Information:java:   at com.sun.tools.javac.tree.JCTree$JCUnary.accept(JCTree.java:1746)
Information:java:   at com.sun.tools.javac.tree.TreeTranslator.visitExec(TreeTranslator.java:245)
Information:java:   at com.sun.tools.javac.tree.JCTree$JCExpressionStatement.accept(JCTree.java:1296)
Information:java:   at com.sun.tools.javac.tree.TreeTranslator.translate(TreeTranslator.java:70)
Information:java:   at com.sun.tools.javac.tree.TreeTranslator.visitBlock(TreeTranslator.java:162)
Information:java:   at com.sun.tools.javac.comp.Lower.visitBlock(Lower.java:3561)
Information:java:   at com.sun.tools.javac.tree.JCTree$JCBlock.accept(JCTree.java:909)
Information:java:   at com.sun.tools.javac.tree.TreeTranslator.visitMethodDef(TreeTranslator.java:145)
Information:java:   at com.sun.tools.javac.comp.Lower.visitMethodDefInternal(Lower.java:2828)
Information:java:   at com.sun.tools.javac.comp.Lower.visitMethodDef(Lower.java:2737)
Information:java:   at com.sun.tools.javac.tree.JCTree$JCMethodDecl.accept(JCTree.java:778)
Information:java:   at com.sun.tools.javac.comp.Lower.visitClassDef(Lower.java:2508)
Information:java:   at com.sun.tools.javac.tree.JCTree$JCClassDecl.accept(JCTree.java:693)
Information:java:   at com.sun.tools.javac.comp.Lower.translate(Lower.java:2390)
Information:java:   at com.sun.tools.javac.comp.Lower.translateTopLevelClass(Lower.java:3932)
Information:java:   at com.sun.tools.javac.main.JavaCompiler.desugar(JavaCompiler.java:1512)
Information:java:   at com.sun.tools.javac.main.JavaCompiler.desugar(JavaCompiler.java:1356)
Information:java:   at com.sun.tools.javac.main.JavaCompiler.compile2(JavaCompiler.java:901)
Information:java:   at com.sun.tools.javac.main.JavaCompiler.compile(JavaCompiler.java:860)
Information:java:   at com.sun.tools.javac.main.Main.compile(Main.java:523)
Information:java:   at com.sun.tools.javac.api.JavacTaskImpl.doCall(JavacTaskImpl.java:129)
Information:java:   at com.sun.tools.javac.api.JavacTaskImpl.call(JavacTaskImpl.java:138)
Information:java:   at org.jetbrains.jps.javac.JavacMain.compile(JavacMain.java:168)
Information:java:   at org.jetbrains.jps.incremental.java.JavaBuilder.compileJava(JavaBuilder.java:382)
Information:java:   at org.jetbrains.jps.incremental.java.JavaBuilder.compile(JavaBuilder.java:296)
Information:java:   at org.jetbrains.jps.incremental.java.JavaBuilder.doBuild(JavaBuilder.java:204)
Information:java:   at org.jetbrains.jps.incremental.java.JavaBuilder.build(JavaBuilder.java:176)
Information:java:   at org.jetbrains.jps.incremental.IncProjectBuilder.runModuleLevelBuilders(IncProjectBuilder.java:1202)
Information:java:   at org.jetbrains.jps.incremental.IncProjectBuilder.runBuildersForChunk(IncProjectBuilder.java:877)
Information:java:   at org.jetbrains.jps.incremental.IncProjectBuilder.buildTargetsChunk(IncProjectBuilder.java:948)
Information:java:   at org.jetbrains.jps.incremental.IncProjectBuilder.buildChunkIfAffected(IncProjectBuilder.java:840)
Information:java:   at org.jetbrains.jps.incremental.IncProjectBuilder.buildChunks(IncProjectBuilder.java:665)
Information:java:   at org.jetbrains.jps.incremental.IncProjectBuilder.runBuild(IncProjectBuilder.java:372)
Information:java:   at org.jetbrains.jps.incremental.IncProjectBuilder.build(IncProjectBuilder.java:193)
Information:java:   at org.jetbrains.jps.cmdline.BuildRunner.runBuild(BuildRunner.java:137)
Information:java:   at org.jetbrains.jps.cmdline.BuildSession.runBuild(BuildSession.java:293)
Information:java:   at org.jetbrains.jps.cmdline.BuildSession.run(BuildSession.java:124)
Information:java:   at org.jetbrains.jps.cmdline.BuildMain$MyMessageHandler$1.run(BuildMain.java:242)
Information:java:   at org.jetbrains.jps.service.impl.SharedThreadPoolImpl$1.run(SharedThreadPoolImpl.java:41)
Information:java:   at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
Information:java:   at java.util.concurrent.FutureTask.run(FutureTask.java:266)
Information:java:   at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
Information:java:   at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
Information:java:   at java.lang.Thread.run(Thread.java:745)
Information:java: Errors occurred while compiling module 'testAGH'
Information:2015-10-23 14:23 - Compilation completed with 1 error and 0 warnings in 671ms
Error:java: Compilation failed: internal java compiler error

为什么 Java 编译失败？

最佳答案

这显然是一个编译器错误。您应该按照输出指示提交错误，但既然您问过为什么，我会尝试探索一下:)

JDK langtools repo包含 javac 的代码。我浏览了几个不同的 builds但无法找到行号与堆栈跟踪匹配的版本(我不确定如何 match a Java version to a build number )，所以我要离开最近的构建，b132 .

如您所见，根本问题是 com.sun.tools.javac.code.Symbol 中的 NullPointerException在 Symbol.ClassSymbol.isSubClass() .这就是问题的根源。在堆栈跟踪中向上看，我们可以看到 access() 调用 accessSymbol()，然后是 accessClass()，然后到达 isSubClass()。因此我们可以推断，编译器在失败时试图验证子类是否允许访问 super.value。

在不知道 NPE 发生在哪条线上的情况下，很难查明确切的问题，所以不幸的是这里的事情变得模糊了。由于此失败仅在我们尝试递增并设置(++ 或 +=)字段时发生，并且仅当我们将其称为 super 时才会发生.value，我们希望看到一些与转换、自动装箱、赋值或算术相关的代码。唉，isSubClass() 中的任何内容似乎都与这些无关。

鉴于 isSubClass() 中似乎没有任何罪证，我的猜测是 Lower.accessClass()将 null 传递给 isSubClass()。此方法中向 isSubClass() 传递了三个值:字段 currentClass (作为c，这是“当前封闭的类”)，sym.owner(我认为sym是我们的值 字段，我不知道它的 owner 是什么，但大概是它在其中声明的类)和 types，它看起来总是设置为非空值(value)。所以它要么是 currentClass 要么是 sym.owner，并且在 Lower.access() 中有对 sym.owner 的引用 NPE较早，所以这似乎也是非空的。

所以我敢说罪魁祸首是 Lower.currentClass 由于某种原因为 null。由于 currentClass 是包私有(private)的非最终字段，我不会费心去确定它此时是否可以为 null，但它似乎可能的。 isSubClass() 当然还有其他几个可能的罪魁祸首，所以我很可能是错的。

不确定，但我希望这能提供信息!如果我了解更多，我一定会更新。

关于编译简单程序时 Java 编译器失败，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/33302349/