在 Java 8 中，給定 package 中的超類Super和 package 中a的子類Sub，b它們有一個內部類SubInner：// Super.javapackage a;public abstract class Super {   private long value;   protected final void setValue(long value) {      this.value = value;   }}//Sub.javapackage b;public class Sub extends Super {  public void foo() {    new SubInner().foo();  }  private class SubInner {    void foo() {      Optional.of(1L).ifPresent(Sub.this::setValue); // Will throw IllegalAccessError at runtime.      Optional.of(1L).ifPresent(t -> setValue(t)); // However, lambda works.      setValue(1L); // also works.    }  }}我的問題是，為什么方法引用在這種情況下不起作用，而普通方法調用可以訪問超類方法setValue？另外，如果我嘗試這樣做Sub.super::setValue，代碼將無法編譯，并且錯誤似乎與運行時錯誤一致：setValuehas protected access in a.Super.Exception in thread "main" java.lang.BootstrapMethodError: java.lang.IllegalAccessError: tried to access method a.Super.setValue(J)V from class b.Sub$SubInner    at b.Sub$SubInner.foo(Sub.java:14)    at b.Sub.foo(Sub.java:10)    at b.Sub.main(Sub.java:22)Caused by: java.lang.IllegalAccessError: tried to access method a.Super.setValue(J)V from class b.Sub$SubInner    at java.lang.invoke.MethodHandleNatives.resolve(Native Method)    at java.lang.invoke.MemberName$Factory.resolve(MemberName.java:975)    at java.lang.invoke.MemberName$Factory.resolveOrFail(MemberName.java:1000)    at java.lang.invoke.MethodHandles$Lookup.resolveOrFail(MethodHandles.java:1394)    at java.lang.invoke.MethodHandles$Lookup.linkMethodHandleConstant(MethodHandles.java:1750)    at java.lang.invoke.MethodHandleNatives.linkMethodHandleConstant(MethodHandleNatives.java:477)    ... 3 more