Android退出程序时弹出对话框确认退出

public class MainActivity extends AppCompatActivity {

    Button exitButton;

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

        exitButton = (Button)findViewById(R.id.exit);
        exitButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                AlertDialog alertDialog = new AlertDialog.Builder(MainActivity.this)
                        .setTitle("退出程序")
                        .setMessage("是否退出程序")
                        .setPositiveButton("确定", new DialogInterface.OnClickListener() {
                            @Override
                            public void onClick(DialogInterface dialogInterface, int i) {
                                finish();
                            }
                        })
                        .setNegativeButton("取消", new DialogInterface.OnClickListener() {
                            @Override
                            public void onClick(DialogInterface dialogInterface, int i) {
                                return;
                            }
                        }).create();
                alertDialog.show();
            }
        });
    }
}