code: static Method findPrivateMethod(Class<?> cl, String methodName,
              Class<?>[] param) {
          try {
              Method method = cl.getDeclaredMethod(methodName, param);
              if (Modifier.isPrivate(method.getModifiers()) && method.getReturnType() == void.class) {
                  method.setAccessible(true);
                  return method;
              }
          } catch (NoSuchMethodException nsm) {
              // Ignored
          }
          return null;
      }
docs: Return the java.lang.reflect.Method if class <code>cl</code> implements
  private <code>methodName</code> . Return null otherwise.
  
  @param cl
  a java.lang.Class which to test
  @return {@code java.lang.reflect.Method} if the class implements
  writeReplace {@code null} if the class does not implement
  writeReplace