toast

MainActivity.java

....
public class MainActivity extends AppCompatActivity {
    private Button btnSimpleToast,btnPositionedToast,btnCustomToast;

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

        btnSimpleToast = findViewById(R.id.btn_simple_toast);
        btnPositionedToast = findViewById(R.id.btn_positioned_toast);
        btnCustomToast = findViewById(R.id.btn_custom_toast);
....