java中如何在Main方法中访问同名变量不同类变量

Question

Accessing Same Name Data Members In Main Method Using obj Object not creating object in Class A and Class B.

class A {
  int i = 10;
}
class B extends A {
 int i = 20;
}
class C extends B {
  int i = 30;
}
public class Main {
  public static void main (String[] args)   {
    C obj = new C ();
    System.out.println (obj.i);
    //How to access Class A variable
    //How to access Class B Variable
  }
}

Print Class A Variable Print Class B Variable Without Creating Object of Class A and Class B.

Answer 1

System.out.println (((A) obj).i); and System.out.println (((B) obj).i); respectively. If they were protected fields, they would be inherited. As is, they are hidden ( shadowed ) package-private fields.

Since you've now mentioned that you cannot use a simple cast, the next best option (I can think of) is reflection . You can iterate the Field (s), find the field named i , make it accessible and then print it (and the class name). For example,

try {
    Class<?>[] classes = { A.class, B.class, C.class };
    for (Class<?> cls : classes) {
        for (Field f : cls.getDeclaredFields()) {
            if (f.getName().equals("i")) {
                f.setAccessible(true);
                System.out.printf("%s %s%n", cls.getSimpleName(), f.get(obj));
            }
        }
    }
} catch (IllegalArgumentException | IllegalAccessException | SecurityException e) {
    e.printStackTrace();
}

Outputs

A 10
B 20
C 30

Answer 2

Use the Reflection. You can get the super class and get the i value. This approach don't use the typeCasting, create object and statie member. I think it will help you.

class A {
    int i = 10;
}
class B extends A {
    int i = 20;
}
class C extends B {
    int i = 30;
}
public class Main {
    public static void main (String[] args)   {
        try {
            C obj = new C();
            System.out.println(obj.i);
            // get the Class B
            Class b = obj.getClass().getSuperclass();
            System.out.println(b.getDeclaredField("i").getInt(obj));
            // get the Class A
            Class a = b.getSuperclass();
            System.out.println(a.getDeclaredField("i").getInt(obj));
        } catch (Exception e) {
            // ignore
        }

        // Output
        // 30
        // 20
        // 10
    }
}