内部类的构造函数引用在运行时因VerifyError而失败

Question

我正在使用lambda为内部类构造函数创建供应商ctx -> new SpectatorSwitcher(ctx).IntelliJ建议我将其SpectatorSwitcher::new改为.SpectatorSwitcher是我正在使用的类的非静态内部类.建议的代码编译得很好(使用maven)但我在执行时得到以下VerifyError:

Exception in thread "main" java.lang.VerifyError: Bad type on operand stack
Exception Details:
  Location:
    Test.lambda$runTest$8(LTest$Worker;)V @2: invokedynamic
  Reason:
    Type 'Test$Worker' (current frame, stack[1]) is not assignable to 'Test'
  Current Frame:
    bci: @2
    flags: { }
    locals: { 'Test$Worker' }
    stack: { 'Test$Worker', 'Test$Worker' }
  Bytecode:
    0000000: 2a2a ba00 0b00 00b6 000c b1            

    at java.lang.Class.getDeclaredMethods0(Native Method)
    at java.lang.Class.privateGetDeclaredMethods(Class.java:2688)
    at java.lang.Class.getMethod0(Class.java:2937)
    at java.lang.Class.getMethod(Class.java:1771)
    at sun.launcher.LauncherHelper.validateMainClass(LauncherHelper.java:544)
    at sun.launcher.LauncherHelper.checkAndLoadMain(LauncherHelper.java:526)

为什么javac/maven在编译时没有失败但仍然产生无效的字节代码？

编辑:问题似乎比简单调用复杂得多,这是重现它所需的代码:

import java.util.function.Function;

/**
 * @author Yawkat
 */
public class Test {
    public static void main(String[] args) { new Test().runTest(); }

    private void runTest() {
        Worker worker = new Worker();
        run(() -> worker.print(field -> new SomeClass(field)));
        run(() -> worker.print(SomeClass::new));
    }

    private void run(Runnable runnable) {
        runnable.run();
    }

    private class SomeClass {
        final Object field;

        SomeClass(Object field) {
            this.field = field;
        }
    }

    private static class Worker {
        void print(Function<Object, Object> i) {
            System.out.println(i.apply(null));
        }
    }
}

Answer 1

即使把我的头撞到字节码上差不多一个小时之后,我也无法得出一个合理的结论,为什么会发生这种情况.令人惊讶的是,将您的方法更改为:

private void runTest() {
    Worker worker = new Worker();
    run(() -> worker.print(field -> new SomeClass(field)));
    Function<Object, Object> function = SomeClass::new;
    run(() -> worker.print(function));
}

工作良好.另外,摆脱run()方法调用,只需调用worker.print():

private void runTest() {
    Worker worker = new Worker();
    worker.print(field -> new SomeClass(field));
    worker.print(SomeClass::new);
}

也有效.

看起来像在你的情况下使用构造函数引用无法将封闭的Test类实例传递给SomeClass所需的构造函数.虽然这里的两个案例能够将Test实例传递给SomeClass构造函数.

但我无法说出具体原因.上述推理可能是错误的.但是在完成那些工作方法后我才刚刚谈到这一点.

你可能想要通过lambda翻译来理解内在的工作.我还不太清楚如何翻译lambdas和方法引用.

我在lambda邮件列表中找到了一个关于类似问题的线程.此外,这个SO帖子也是相关的.

以下runtTest()方法:

public void runTest() {
    Worker worker = new Worker();
    run(() -> worker.print((field) -> new SomeClass(field)));
    run(() -> worker.print(SomeClass::new));

    Function<Object, Object> func = SomeClass::new;
    run(() -> worker.print(func));

    worker.print(SomeClass::new);
}

编译为以下字节码:

  public void runTest();
    Code:
       0: new           #2                  // class SO$Worker
       3: dup
       4: invokespecial #3                  // Method SO$Worker."<init>":()V
       7: astore_1
       8: aload_0
       9: aload_0
      10: aload_1
      11: invokedynamic #4,  0              // InvokeDynamic #0:run:(LSO;LSO$Worker;)Ljava/lang/Runnable;
      16: invokevirtual #5                  // Method run:(Ljava/lang/Runnable;)V
      19: aload_0
      20: aload_1
      21: invokedynamic #6,  0              // InvokeDynamic #1:run:(LSO$Worker;)Ljava/lang/Runnable;
      26: invokevirtual #5                  // Method run:(Ljava/lang/Runnable;)V
      29: aload_0
      30: invokedynamic #7,  0              // InvokeDynamic #2:apply:(LSO;)Ljava/util/function/Function;
      35: astore_2
      36: aload_0
      37: aload_1
      38: aload_2
      39: invokedynamic #8,  0              // InvokeDynamic #3:run:(LSO$Worker;Ljava/util/function/Function;)Ljava/lang/Runnable;
      44: invokevirtual #5                  // Method run:(Ljava/lang/Runnable;)V
      47: aload_1
      48: aload_0
      49: invokedynamic #7,  0              // InvokeDynamic #2:apply:(LSO;)Ljava/util/function/Function;
      54: invokevirtual #9                  // Method SO$Worker.print:(Ljava/util/function/Function;)V
      57: return

我只能看到第二个run()方法调用没有传递LSO参数,而其他方法确实传递了它.您可以运行命令- javap -c -s -verbose Test,看到的引导方法#0,#1等等.我想我们可以肯定地说,这是一个错误.也许你可以提交一个.