可以用android studio代码写出来吗

当然可以，以下是一些示例代码：

1. 产品介绍和选购功能页面的实现代码：

public class ProductActivity extends AppCompatActivity implements ProductAdapter.OnItemClickListener {
    
    private RecyclerView mRecyclerView;
    private ProductAdapter mAdapter;
    private List<Product> mProductList;
    private SQLiteDatabase mDatabase;
    
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_product);
        
        // 初始化RecyclerView
        mRecyclerView = findViewById(R.id.recycler_view);
        mRecyclerView.setLayoutManager(new LinearLayoutManager(this));
        
        // 初始化数据库
        DBHelper dbHelper = new DBHelper(this);
        mDatabase = dbHelper.getWritableDatabase();
        
        // 加载商品数据
        mProductList = new ArrayList<>();
        Cursor cursor = mDatabase.query("product", null, null, null, null, null, null);
        while (cursor.moveToNext()) {
            int id = cursor.getInt(cursor.getColumnIndex("id"));
            String name = cursor.getString(cursor.getColumnIndex("name"));
            double price = cursor.getDouble(cursor.getColumnIndex("price"));
            String description = cursor.getString(cursor.getColumnIndex("description"));
            String image = cursor.getString(cursor.getColumnIndex("image"));
            Product product = new Product(id, name, price, description, image);
            mProductList.add(product);
        }
        cursor.close();
        
        // 初始化适配器
        mAdapter = new ProductAdapter(mProductList);
        mAdapter.setOnItemClickListener(this);
        mRecyclerView.setAdapter(mAdapter);
    }
    
    @Override
    public void onItemClick(int position) {
        // 处理商品选购事件，将选购信息保存到数据库
        Product product = mProductList.get(position);
        ContentValues values = new ContentValues();
        values.put("name", product.getName());
        values.put("price", product.getPrice());
        values.put("quantity", 1);
        values.put("subtotal", product.getPrice());
        mDatabase.insert("cart", null, values);
        Toast.makeText(this, "已加入购物车", Toast.LENGTH_SHORT).show();
    }
    
    @Override
    protected void onDestroy() {
        super.onDestroy();
        mDatabase.close();
    }
}

2. 购物车展示功能页面的实现代码：

public class CartActivity extends AppCompatActivity implements CartAdapter.OnItemClickListener {
    
    private RecyclerView mRecyclerView;
    private CartAdapter mAdapter;
    private List<CartItem> mCartList;
    private SQLiteDatabase mDatabase;
    
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_cart);
        
        // 初始化RecyclerView
        mRecyclerView = findViewById(R.id.recycler_view);
        mRecyclerView.setLayoutManager(new LinearLayoutManager(this));
        
        // 初始化数据库
        DBHelper dbHelper = new DBHelper(this);
        mDatabase = dbHelper.getWritableDatabase();
        
        // 加载购物车数据
        mCartList = new ArrayList<>();
        Cursor cursor = mDatabase.query("cart", null, null, null, null, null, null);
        while (cursor.moveToNext()) {
            int id = cursor.getInt(cursor.getColumnIndex("id"));
            String name = cursor.getString(cursor.getColumnIndex("name"));
            double price = cursor.getDouble(cursor.getColumnIndex("price"));
            int quantity = cursor.getInt(cursor.getColumnIndex("quantity"));
            double subtotal = cursor.getDouble(cursor.getColumnIndex("subtotal"));
            CartItem item = new CartItem(id, name, price, quantity, subtotal);
            mCartList.add(item);
        }
        cursor.close();
        
        // 初始化适配器
        mAdapter = new CartAdapter(mCartList);
        mAdapter.setOnItemClickListener(this);
        mRecyclerView.setAdapter(mAdapter);
    }
    
    @Override
    public void onItemClick(int position, int quantity) {
        // 处理修改购物车商品数量事件，更新数据库
        CartItem item = mCartList.get(position);
        item.setQuantity(quantity);
        item.setSubtotal(item.getPrice() * quantity);
        ContentValues values = new ContentValues();
        values.put("quantity", quantity);
        values.put("subtotal", item.getSubtotal());
        mDatabase.update("cart", values, "id = ?", new String[] {String.valueOf(item.getId())});
        mAdapter.notifyItemChanged(position);
    }
    
    @Override
    public void onDeleteClick(int position) {
        // 处理删除购物车商品事件，从数据库中删除
        CartItem item = mCartList.get(position);
        mDatabase.delete("cart", "id = ?", new String[] {String.valueOf(item.getId())});
        mCartList.remove(position);
        mAdapter.notifyItemRemoved(position);
    }
    
    @Override
    protected void onDestroy() {
        super.onDestroy();
        mDatabase.close();
    }
}

3. 外网链接功能的实现代码：

public class MainActivity extends AppCompatActivity {
    
    private Button mLinkButton;
    
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        
        // 初始化外网链接按钮
        mLinkButton = findViewById(R.id.link_button);
        mLinkButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                // 跳转到指定网址
                Intent intent = new Intent(Intent.ACTION_VIEW);
                intent.setData(Uri.parse("https://www.example.com"));
                startActivity(intent);
            }
        });
    }
}