public class MainActivity extends AppCompatActivity {
    
    public TextView myText;

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

        myText = findViewById(R.id.textView);

    }

    public void myAction(View view) {
        myText.setText("AHOJ TAMZ");
    }
}