How to use spinner

MainActivity.java

public class MainActivity extends AppCompatActivity implements AdapterView.OnItemSelectedListener {

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

        Spinner spinner = findViewById(R.id.spinner);
        spinner.setOnItemSelectedListener(this);
    }

    // 項目が選択された場合
    @Override
    public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
        Toast.makeText(this, parent.getSelectedItem() + "が選択されました", Toast.LENGTH_SHORT).show();
    }

    // 項目が選択されなかった場合
    @Override
    public void onNothingSelected(AdapterView<?> parent) {
    }
}