java.lang.reflect.Field (get* and set*) and Method (invoke) base their access check on the declaring class. This is contrary to the JLS, which defines accessibility in terms of the reference type. Consider the following:

package foo;

class X {
    public int i;
}

package foo;

public class Y extends X {
    public static Object get() { return new Z(); }
}

package foo;

class Z extends Y {}

package bar;

import foo.Y;

public class T {
    public static void main(String[] args) {
Y y = new Y();
int i = y.i;
try {
y.getClass().getField("i").getInt(y);
} catch (Exception e) {
e.printStackTrace();
}
Object z = Y.get();
i = ((Y)z).i;
try {
z.getClass().getField("i").getInt(z);
} catch (Exception e) {
e.printStackTrace();
}
    }
}

Both of the getInt calls throw IllegalAccessException, contrary to what the compiler allows.

At runtime you need to check if there exists some class, between the declaring class and the actual class (inclusive), that is public. This could be a bit messy for interface methods, since there isn't a single linear chain to search.