Question

Presume we have two different packages… one package can’t be accessed but we like to know the value of a complex field called b.

public class A {
    private String  whatever;
    private B       b;

    private static class B {
         final ArrayList<Z> c   = new ArrayList<Z>();

         private void addItem(Z z) {
                this.c.add(z);
         }

         private Z getItem(int nr) {
                return this.c.get(nr);
          }
     }
}

public class Reflect extends A {
      public static void main(String[] args) throws NoSuchFieldException, SecurityException {
            Reflect ref = new Reflect();
            Class getA = ref.getClass().getSuperclass();
            Field getB = getDeclaredField("b");
            getB.setAccessible(true);
            Class bInst = getB.getClass();
            Method bMeth = bInst.getMethod("getItem", Integer.TYPE);
            Object zInst = bMeth.invoke(new Integer(123));
      }
}

How can I get the value if I don’t get the complex type B from the package ?
Still get java.lang.NoSuchMethodException: stackOver.A.getItem(int) even I set the field gstB accessible ….

Answer 1

The only thing you are missing is that getField only gives you public accessible fields.

 Field getB = getA.getDeclaredField("b");

will give you any field of that class.

---

A longer example

class Main {
    public static class A {
        private String whatever;
        private B b = new B();

        private static class B {
            final ArrayList<String> c = new ArrayList<String>();

            private void addItem(String z) {
                this.c.add(z);
            }

            private String getItem(int nr) {
                return this.c.get(nr);
            }
        }
    }

    public static class Reflect extends A {
        public static void main(String... ignored) throws Exception {
            Reflect ref = new Reflect();
            Class getA = ref.getClass().getSuperclass();
            Field getB = getA.getDeclaredField("b");
            getB.setAccessible(true);
            Object b = getB.get(ref);

            Method addItem = b.getClass().getDeclaredMethod("addItem", String.class);
            addItem.setAccessible(true);
            addItem.invoke(b, "Hello");

            Method getItem = b.getClass().getDeclaredMethod("getItem", int.class);
            getItem.setAccessible(true);
            String hi = (String) getItem.invoke(b, 0);
            System.out.println(hi);
        }
    }
}

prints

Hello