Stuck on wiring up widgets

I used the following code on page 21.

public class QuizActivity extends AppCompatActivity {
private Button mtrueButton;
private Button mfalseButton;
protected void OnCreate(Bundle savedInstanceState) {

Even though I was sure to have the code look exactly like it looks in the book, I got the following error message.
Installed Build Tools revision 30.0.2 is corrupted. Remove and install again using the SDK Manager.
Does this mean that I’m going to have to uninstall android studio, reinstall it and start from scratch?
I realize the the book is 3 years old and the version of Android studio that I’m using is the latest. With that, was this a coding error on my end?

If this is not either of the aforementioned, how do I fix the problem to move forward.

Any assistance in this matter would be greatly appreciated.



  1. File > Settings > Appearance & Behavior > System Settings > Android SDK
  2. Open SDK Tools tab, at the bottom-right, click Show Package Details
  3. Find Android SDK Build-Tools and unchecked the checkbox next to 30.0.2
  4. Click apply in the bottom of the window. That will delete the component.
  5. Now check the checkbox next to 30.0.2
  6. Click apply in the bottom of the window

Great. Thank you! <3 <3