How to set button click event with java 2

MainActivity.java

public class MainActivity extends AppCompatActivity implements View.OnClickListener {

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

        findViewById(R.id.btn1).setOnClickListener(this);
    }

    @Override
    public void onClick(View v) {
        Snackbar.make(v, "ボタン１が押されました", Snackbar.LENGTH_SHORT).show();
    }
}