HiddenImplementation.java

// Sneaking around package access.
package thinkinginjava.typeinfo;

import java.lang.reflect.*;

import thinkinginjava.typeinfo.interfacea.A;
import thinkinginjava.typeinfo.packageaccess.HiddenC;

public class HiddenImplementation {
	public static void main(String[] args) throws Exception {
		A a = HiddenC.makeA();
		a.f();
		System.out.println(a.getClass().getName());
		// Compile error: cannot find symbol 'C':
		/*
		 * if(a instanceof C) { C c = (C)a; c.g(); }
		 */
		// Oops! Reflection still allows us to call g():
		callHiddenMethod(a, "g");
		// And even methods that are less accessible!
		callHiddenMethod(a, "u");
		callHiddenMethod(a, "v");
		callHiddenMethod(a, "w");
	}

	static void callHiddenMethod(Object a, String methodName) throws Exception {
		Method g = a.getClass().getDeclaredMethod(methodName);
		g.setAccessible(true);
		g.invoke(a);
	}
}