[Android] 안드로이드 알림창 만들기

public class MainActivity extends AppCompatActivity {

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

        textView = (TextView)findViewById(R.id.textView);

        Button button = (Button)findViewById(R.id.button);

        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                showMessage();
            }
        });
    }

    public void showMessage(){
        AlertDialog.Builder builder = new AlertDialog.Builder(this);
        builder.setTitle("안내");
        builder.setMessage("종료하시겠습니까?");
        builder.setIcon(android.R.drawable.ic_dialog_alert);
        builder.setPositiveButton("예", new DialogInterface.OnClickListener() {
            @Override
            public void onClick(DialogInterface dialog, int which) {
                Snackbar.make(textView,"예 버튼이 눌렸습니다.",Snackbar.LENGTH_LONG).show();
            }
        });

        builder.setNegativeButton("아니오", new DialogInterface.OnClickListener() {
            @Override
            public void onClick(DialogInterface dialog, int which) {
                Snackbar.make(textView,"아니오 버튼이 눌렸습니다.",Snackbar.LENGTH_LONG).show();
            }
        });
        AlertDialog dialog = builder.create();
        dialog.show();
    }
}