写出在 Java 类文件中实现菜品列表的初始化、购物车的添加和删除、结算金额的计算等功能的代码

好的，以下是一个简单的 Java 类文件，包含了菜品列表的初始化、购物车的添加和删除、结算金额的计算等功能的代码：

public class MainActivity extends AppCompatActivity {

    private List<Dish> menuList;   // 菜品列表
    private List<Dish> cartList;   // 购物车列表
    private ListView menuListView; // 菜品列表控件
    private ListView cartListView; // 购物车列表控件
    private TextView totalPriceTextView; // 结算金额控件
    private Button checkoutButton; // 结算按钮控件

    private DishAdapter menuAdapter; // 菜品列表适配器
    private CartAdapter cartAdapter; // 购物车列表适配器

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

        // 获取布局文件中的控件
        menuListView = findViewById(R.id.lv_menu);
        cartListView = findViewById(R.id.lv_cart);
        totalPriceTextView = findViewById(R.id.tv_total_price);
        checkoutButton = findViewById(R.id.btn_checkout);

        // 初始化菜品列表和购物车列表
        initMenu();
        initCart();

        // 设置菜品列表的点击事件，将菜品添加到购物车列表中
        menuListView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
                Dish dish = menuList.get(position);
                cartList.add(dish);
                cartAdapter.notifyDataSetChanged();
                updateTotalPrice();
            }
        });

        // 设置购物车列表的长按事件，从购物车列表中删除该项
        cartListView.setOnItemLongClickListener(new AdapterView.OnItemLongClickListener() {
            @Override
            public boolean onItemLongClick(AdapterView<?> parent, View view, int position, long id) {
                cartList.remove(position);
                cartAdapter.notifyDataSetChanged();
                updateTotalPrice();
                return true;
            }
        });

        // 设置结算按钮的点击事件，计算购物车中所有菜品的价格总和
        checkoutButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                int totalPrice = 0;
                for (Dish dish : cartList) {
                    totalPrice += dish.getPrice();
                }
                Toast.makeText(MainActivity.this, "总价：" + totalPrice + "元", Toast.LENGTH_SHORT).show();
            }
        });
    }

    // 初始化菜品列表
    private void initMenu() {
        menuList = new ArrayList<>();
        menuList.add(new Dish("宫保鸡丁", 20));
        menuList.add(new Dish("鱼香肉丝", 18));
        menuList.add(new Dish("辣子鸡", 22));
        menuAdapter = new DishAdapter(this, R.layout.dish_item, menuList);
        menuListView.setAdapter(menuAdapter);
    }

    // 初始化购物车列表
    private void initCart() {
        cartList = new ArrayList<>();
        cartAdapter = new CartAdapter(this, R.layout.cart_item, cartList);
        cartListView.setAdapter(cartAdapter);
    }

    // 更新结算金额
    private void updateTotalPrice() {
        int totalPrice = 0;
        for (Dish dish : cartList) {
            totalPrice += dish.getPrice();
        }
        totalPriceTextView.setText("总价：" + totalPrice + "元");
    }

    // 菜品类
    private class Dish {
        private String name; // 名称
        private int price;   // 价格

        public Dish(String name, int price) {
            this.name = name;
            this.price = price;
        }

        public String getName() {
            return name;
        }

        public int getPrice() {
            return price;
        }
    }

    // 菜品适配器类
    private class DishAdapter extends ArrayAdapter<Dish> {
        private int resourceId;

        public DishAdapter(Context context, int resourceId, List<Dish> objects) {
            super(context, resourceId, objects);
            this.resourceId = resourceId;
        }

        @Override
        public View getView(int position, View convertView, ViewGroup parent) {
            Dish dish = getItem(position);
            View view = LayoutInflater.from(getContext()).inflate(resourceId, parent, false);
            TextView nameTextView = view.findViewById(R.id.tv_dish_name);
            TextView priceTextView = view.findViewById(R.id.tv_dish_price);
            nameTextView.setText(dish.getName());
            priceTextView.setText(dish.getPrice() + "元");
            return view;
        }
    }

    // 购物车适配器类
    private class CartAdapter extends ArrayAdapter<Dish> {
        private int resourceId;

        public CartAdapter(Context context, int resourceId, List<Dish> objects) {
            super(context, resourceId, objects);
            this.resourceId = resourceId;
        }

        @Override
        public View getView(int position, View convertView, ViewGroup parent) {
            Dish dish = getItem(position);
            View view = LayoutInflater.from(getContext()).inflate(resourceId, parent, false);
            TextView nameTextView = view.findViewById(R.id.tv_cart_name);
            TextView priceTextView = view.findViewById(R.id.tv_cart_price);
            nameTextView.setText(dish.getName());
            priceTextView.setText(dish.getPrice() + "元");
            return view;
        }
    }
}

以上代码实现了菜品列表的初始化、购物车的添加和删除、结算金额的计算等功能。其中，Dish 类表示一个菜品，DishAdapter 类和 CartAdapter 类分别是菜品列表和购物车列表的适配器类，用于将菜品数据显示在 ListView 控件上。在 onCreate 方法中，我们初始化了菜品列表和购物车列表，并设置了菜品列表的点击事件、购物车列表的长按事件和结算按钮的点击事件，以实现购物车的添加和删除、结算金额的计算等功能。