如何從私有靜態內部類訪問變量

Question

我有一個這樣的類結構：

public class Outer{
    private Outer.Inner personal;
    public Outer(){
        //processing.
        //personal assigned value
    }
    ........
    private static class Inner {
        private final Set<String> innerPersonal;
        Inner(){
             innerPersonal=new HashSet<>();
             //populate innerPersonal
        }
    }
}

我在程序中得到一個外部對象，如何使用反射在程序中提取innerPersonal 。

Answer 1

當您要執行的外部代碼Outer ，您不能使用Outer.Inner.class參閱您的static inner class ，因為它是private的，所以這里我提出一個辦法，只會讓該領域的第一個值personal ，然后調用最終返回此inner class的字段的返回值（假定它不為null getClass()上的getClass() ，該inner class也允許訪問其內部字段innerPersonal 。

Outer outer = ...
// Get the declared (private) field personal from the public class Outer
Field  personalField = Outer.class.getDeclaredField("personal");
// Make it accessible otherwise you won't be able to get the value as it is private
personalField.setAccessible(true);
// Get the value of the field in case of the instance outer
Object personal =  personalField.get(outer);
// Get the declared (private) field innerPersonal from the private static class Inner
Field  innerPersonalField = personal.getClass().getDeclaredField("innerPersonal");
// Make it accessible otherwise you won't be able to get the value as it is private
innerPersonalField.setAccessible(true);
// Get the value of the field in case of the instance personal
Set<String> innerPersonal = (Set<String>)innerPersonalField.get(personal);

Answer 2

@Retention(RetentionPolicy.RUNTIME)
    public @interface Factory {

            Class<?> value();
    }

---

public class Outer{
    private Outer.Inner personal;

    public Outer(){
        //processing.
        //personal assigned value
    }
    @Factory(SomeType.class)
    private static class Inner {
        public final Set<String> innerPersonal;
        Inner(){
             innerPersonal=new HashSet<>();
             //populate innerPersonal
        }
    }    


 }

---

Outer o = new Outer();
Object r = o.getClass().getAnnotationsByType(Factory.class);

---

也許這可行。