public class Victim implements IVictim{
    @Override
    public void f() {
       System.out.println("Victim f()");
    }
    @Override
    public void g() {
        System.out.println("Victim g()");
        f();
     }
 }

//g()
 public void g() {
        System.out.println("Victim g()");
        f();//<------вызов f()
     }

public class Master implements InvocationHandler{
   private Object obj;

    public static Object newInstance(Object obj) {
	return java.lang.reflect.Proxy.newProxyInstance(
	    obj.getClass().getClassLoader(),
	    obj.getClass().getInterfaces(),
	    new Master(obj));
    }

    private Master(Object obj) {
	this.obj = obj;
    }

    public Object invoke(Object proxy, Method m, Object[] args)
	throws Throwable
    {
        Object result;
	try {
	    System.out.println("before method " + m.getName());
	    result = m.invoke(obj, args);
        } catch (InvocationTargetException e) {
	    throw e.getTargetException();
        } catch (Exception e) {
	    throw new RuntimeException("unexpected invocation exception: " +
				       e.getMessage());
	} finally {
	    System.out.println("after method " + m.getName());
	}
	return result;
    }
}