购物是一种常见的消费行为，而且随着互联网技术的发展，越来越多的人开始购物，尤其是在线购物。为了让购物更方便和更高效，我们可以用Java编写一个购物程序。

在这个购物程序中，我们首先需要考虑的是商品的信息存储问题。我们可以使用Java中的数组或者集合来存储商品的信息，比如商品名称、价格、库存等信息。下面是一个商品类的示例：

class Commodity {
  private String name;
  private double price;
  private int quantity;
  public Commodity(String name, double price, int quantity)
    this.name = name;
    this.price = price;
    this.quantity = quantity;
  
  // getter and setter methods
}

接下来，我们需要实现购物车的功能。购物车应该支持添加商品、删除商品、修改商品数量和计算总价等功能。下面是一个购物车类的示例：

import java.util.ArrayList;
import java.util.List;
class ShoppingCart {
  private List
  items;
 
  public ShoppingCart() {
    this.items = new ArrayList<>();
  }
  public boolean addItem(Commodity item) {
    return this.items.add(item);
  }
  public boolean removeItem(Commodity item) {
    return this.items.remove(item);
  }
  public boolean updateItemQuantity(Commodity item, int quantity) {
    if (!this.items.contains(item))
      return false;
    
    item.setQuantity(quantity);
    return true;
  }
  public double getTotalPrice() {
    double totalPrice = 0;
    for (Commodity item : this.items) {
      totalPrice += item.getPrice() * item.getQuantity();
    }
    return totalPrice;
  }
}

最后，我们需要实现用户界面，让用户可以方便地使用购物程序。用户界面可以使用Java Swing框架来实现。下面是一个用户界面类的示例：

import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
public class ShoppingPanel extends JPanel {
  private JTextField nameField;
  private JTextField priceField;
  private JTextField quantityField;
  private JButton addButton;
  private JButton removeButton;
  private JButton updateButton;
  private JList
  itemList;
 
  private JTextArea totalPriceArea;
  private ShoppingCart shoppingCart;
  public ShoppingPanel() {
    this.shoppingCart = new ShoppingCart();
    this.setLayout(new BorderLayout());
    JPanel controlPanel = new JPanel();
    controlPanel.setLayout(new GridLayout(4, 2));
    this.nameField = new JTextField();
    controlPanel.add(new JLabel("Name:"));
    controlPanel.add(this.nameField);
    this.priceField = new JTextField();
    controlPanel.add(new JLabel("Price:"));
    controlPanel.add(this.priceField);
    this.quantityField = new JTextField();
    controlPanel.add(new JLabel("Quantity:"));
    controlPanel.add(this.quantityField);
    this.addButton = new JButton("Add");
    this.addButton.addActionListener(new ActionListener() {
      @Override
      public void actionPerformed(ActionEvent e) {
        String name = nameField.getText();
        double price = Double.parseDouble(priceField.getText());
        int quantity = Integer.parseInt(quantityField.getText());
        Commodity item = new Commodity(name, price, quantity);
        shoppingCart.addItem(item);
        itemList.updateUI();
        totalPriceArea.setText("Total price: " + shoppingCart.getTotalPrice());
      }
    });
    controlPanel.add(this.addButton);
    this.removeButton = new JButton("Remove");
    this.removeButton.addActionListener(new ActionListener() {
      @Override
      public void actionPerformed(ActionEvent e) {
        Commodity item = itemList.getSelectedValue();
        if (item != null) {
          shoppingCart.removeItem(item);
          itemList.updateUI();
          totalPriceArea.setText("Total price: " + shoppingCart.getTotalPrice());
        }
      }
    });
    controlPanel.add(this.removeButton);
    this.updateButton = new JButton("Update");
    this.updateButton.addActionListener(new ActionListener() {
      @Override
      public void actionPerformed(ActionEvent e) {
        Commodity item = itemList.getSelectedValue();
        if (item != null) {
          int quantity = Integer.parseInt(quantityField.getText());
          shoppingCart.updateItemQuantity(item, quantity);
          itemList.updateUI();
          totalPriceArea.setText("Total price: " + shoppingCart.getTotalPrice());
        }
      }
    });
    controlPanel.add(this.updateButton);
    this.add(controlPanel, BorderLayout.NORTH);
    JPanel listPanel = new JPanel();
    listPanel.setLayout(new BorderLayout());
    this.itemList = new JList<>();
    this.itemList.setModel(new DefaultListModel<>());
    this.itemList.setSelectionMode(ListSelectionModel.SINGLE_SELECTION);
    JScrollPane scrollPane = new JScrollPane(this.itemList);
    listPanel.add(scrollPane, BorderLayout.CENTER);
    this.add(listPanel, BorderLayout.CENTER);
    this.totalPriceArea = new JTextArea();
    this.totalPriceArea.setEditable(false);
    listPanel.add(this.totalPriceArea, BorderLayout.SOUTH);
  }
}

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