Download and Install JDK9

Download and Install Android Studio

Start a new project

Android Studio Overview - Java

Android Studio Overview - Layout

Android Studio Overview - Layout (XML)

First App: Hello Goodbye

Build App

Settings > About > click "Build number" 7 times

Go to Developer Options, Check "USB debugging"

Screenshot

Finishing Java code...

Java code for copy and paste

            
              public class MainActivity extends AppCompatActivity {

                private TextView greetingTextView;
                private Button greetingButton;

                private boolean isHello;

                @Override
                protected void onCreate(Bundle savedInstanceState) {
                  super.onCreate(savedInstanceState);
                  setContentView(R.layout.activity_main);

                  greetingButton = findViewById(R.id.greetingBTN);
                  greetingTextView = findViewById(R.id.greetingTV);

                  initGreeting();

                  greetingButton.setOnClickListener(toggleGreeting);
                }

                private void initGreeting() {
                  isHello = true;
                }

                private final View.OnClickListener toggleGreeting = new View.OnClickListener() {
                  @Override
                  public void onClick(View btn) {
                    if(isHello) {
                      isHello = false;
                      greetingTextView.setText("Goodbye");
                    } else {
                      isHello = true;
                      greetingTextView.setText("Hello");
                    }
                  }
                };
              }