在更高版本的 Java 中，内部类如何访问封闭类的私有成员

我一直在努力理解java中嵌套类的机制.

考虑以下代码:

public class OuterClass {

private String privateOuterField = "Private Outer Field";

public static String publicStaticOuterField = "Public static outer field";

private static String privateStaticOuterField = "private static outer field";


class InnerClass{
    private String privateInnerField = "Private Inner Field";
    
    //non-final static data members not allowed in java 1.8 but allowed in java 17.0
    //private static String innerClassStaticField = "Private Inner Class Static Field";   
    
    public void accessMembers() {
        System.out.println(privateOuterField);
        System.out.println(publicStaticOuterField);
    }
}

static class StaticInnerClass{
    
    private String privateStaticInnerField = "Private Inner Field of static class";
    
    public void accessMembers(OuterClass outer) {
        //System.out.println(privateOuterField);  //error
        System.out.println(outer.privateOuterField);
        System.out.println(publicStaticOuterField);
        System.out.println(privateStaticOuterField);
    }
}
    
public static void main(String[] args) {
    
    OuterClass outerObj = new OuterClass();
    OuterClass.InnerClass innerObj = outerObj.new InnerClass();
    
    StaticInnerClass staticInnerObj = new StaticInnerClass();
    
    innerObj.accessMembers();
    staticInnerObj.accessMembers(outerObj);
    

}

}

我知道内部类是编译器的一种现象，虚拟机并没有意识到它们.内部类被转换为常规类文件，外部类名和内部类名之间用$分隔.

为了更详细地理解这种机制，我try 使用javap-p命令反汇编java 1.8版编译的类文件.

我得到了以下结果:

public class staticNestedClasses.OuterClass {
  private java.lang.String privateOuterField;
  public static java.lang.String publicStaticOuterField;
  private static java.lang.String privateStaticOuterField;
  public staticNestedClasses.OuterClass();
  public static void main(java.lang.String[]);
  static java.lang.String access$000(staticNestedClasses.OuterClass);
  static java.lang.String access$100();
  static {};
}

内部类别:

class staticNestedClasses.OuterClass$InnerClass {
  private java.lang.String privateInnerField;
  final staticNestedClasses.OuterClass this$0;
  staticNestedClasses.OuterClass$InnerClass(staticNestedClasses.OuterClass);
  public void accessMembers();
}

在这里我们可以看到，编译器通过构造函数将外部类的引用传递给内部类，以便判断外部类的字段和方法:

staticNestedClasses.OuterClass$InnerClass(staticNestedClasses.OuterClass);

这个外部类引用存储在final staticNestedClasses.OuterClass this$0中

但是OuterClass$InnerClass类不能通过外部类引用直接访问私有成员，所以每当编译器检测到从内部类访问私有成员时，它都会在外部类中生成访问器方法(或getter方法).

在外部类的反汇编文件中，我们可以看到编译器生成了这些访问器方法.

static java.lang.String access$000(staticNestedClasses.OuterClass);
static java.lang.String access$100();

但当我在java 17.0中编译相同的代码并反汇编类文件时，我得到了以下结果.

外层舱:

public class staticNestedClasses.OuterClass {
  private java.lang.String privateOuterField;
  public static java.lang.String publicStaticOuterField;
  private static java.lang.String privateStaticOuterField;
  public staticNestedClasses.OuterClass();
  public static void main(java.lang.String[]);
  static {};
}

OuterClass$内部类别:

class staticNestedClasses.OuterClass$InnerClass {
  private java.lang.String privateInnerField;
  private static java.lang.String innerClassStaticField;
  final staticNestedClasses.OuterClass this$0;
  staticNestedClasses.OuterClass$InnerClass(staticNestedClasses.OuterClass);
  public void accessMembers();
  static {};
}

这里是compiler did not generate any accessor methods，但代码运行良好.

So how did the inner class access private members of outer class?