Java implementation of Map collection secondary linkage method analysis

Map collection can save key-value mapping relationships, which is very suitable for the data structure required by this example. All province information can be saved as the keys of the Map collection, and each key can save the corresponding city information. This example uses Map The collection implements province and city cascade selection boxes. When province information is selected, the content corresponding to the city drop-down selection box will be changed.

Idea analysis:

1. Create a national (province, municipality, autonomous region) mapping collection, that is, a LinkedHashMap object, and use the put() method of the Map interface to add the specified provinces and cities to the collection. Mapping relationship, where the value is a one-dimensional array of String type.

import java.util.LinkedHashMap;
import java.util.Map;
 
public class CityMap {
    /**
     * 全国（省，直辖市，自治区）映射集合
     */
    public static Map<String,String[]> model=new LinkedHashMap<String, String[]>();
    static{
        model.put("北京", new String[]{"北京"});
        model.put("上海", new String[]{"上海"});
        model.put("天津", new String[]{"天津"});
        model.put("重庆", new String[]{"重庆"});
        model.put("黑龙江", new String[]{"哈尔滨","齐齐哈尔","牡丹江","大庆","伊春","双鸭山","鹤岗","鸡西","佳木斯","七台河","黑河","绥化","大兴安岭"});
        model.put("吉林", new String[]{"长春","延边","吉林","白山","白城","四平","松原","辽源","大安","通化"});
        model.put("辽宁", new String[]{"沈阳","大连","葫芦岛","旅顺","本溪","抚顺","铁岭","辽阳","营口","阜新","朝阳","锦州","丹东","鞍山"});
        model.put("内蒙古", new String[]{"呼和浩特","呼伦贝尔","锡林浩特","包头","赤峰","海拉尔","乌海","鄂尔多斯","通辽"});
        model.put("河北", new String[]{"石家庄","唐山","张家口","廊坊","邢台","邯郸","沧州","衡水","承德","保定","秦皇岛"});
        model.put("河南", new String[]{"郑州","开封","洛阳","平顶山","焦作","鹤壁","新乡","安阳","濮阳","许昌","漯河","三门峡","南阳","商丘","信阳","周口","驻马店"});
        model.put("山东", new String[]{"济南","青岛","淄博","威海","曲阜","临沂","烟台","枣庄","聊城","济宁","菏泽","泰安","日照","东营","德州","滨州","莱芜","潍坊"});
        model.put("山西", new String[]{"太原","阳泉","晋城","晋中","临汾","运城","长治","朔州","忻州","大同","吕梁"});
        model.put("江苏", new String[]{"南京","苏州","昆山","南通","太仓","吴县","徐州","宜兴","镇江","淮安","常熟","盐城","泰州","无锡","连云港","扬州","常州","宿迁"});
        model.put("安徽", new String[]{"合肥","巢湖","蚌埠","安庆","六安","滁州","马鞍山","阜阳","宣城","铜陵","淮北","芜湖","毫州","宿州","淮南","池州"});
        model.put("陕西", new String[]{"西安","韩城","安康","汉中","宝鸡","咸阳","榆林","渭南","商洛","铜川","延安"});
        model.put("宁夏", new String[]{"银川","固原","中卫","石嘴山","吴忠"});
        model.put("甘肃", new String[]{"兰州","白银","庆阳","酒泉","天水","武威","张掖","甘南","临夏","平凉","定西","金昌"});
        model.put("青海", new String[]{"西宁","海北","海西","黄南","果洛","玉树","海东","海南"});
        model.put("湖北", new String[]{"武汉","宜昌","黄冈","恩施","荆州","神农架","十堰","咸宁","襄樊","孝感","随州","黄石","荆门","鄂州"});
        model.put("湖南", new String[]{"长沙","邵阳","常德","郴州","吉首","株洲","娄底","湘潭","益阳","永州","岳阳","衡阳","怀化","韶山","张家界"});
        model.put("浙江", new String[]{"杭州","湖州","金华","宁波","丽水","绍兴","雁荡山","衢州","嘉兴","台州","舟山","温州"});
        model.put("江西", new String[]{"南昌","萍乡","九江","上饶","抚州","吉安","鹰潭","宜春","新余","景德镇","赣州"});
        model.put("福建", new String[]{"福州","厦门","龙岩","南平","宁德","莆田","泉州","三明","漳州"});
        model.put("贵州", new String[]{"贵阳","安顺","赤水","遵义","铜仁","六盘水","毕节","凯里","都匀"});
        model.put("四川", new String[]{"成都","泸州","内江","凉山","阿坝","巴中","广元","乐山","绵阳","德阳","攀枝花","雅安","宜宾","自贡","甘孜州","达州","资阳","广安","遂宁","眉山","南充"});
        model.put("广东", new String[]{"广州","深圳","潮州","韶关","湛江","惠州","清远","东莞","江门","茂名","肇庆","汕尾","河源","揭阳","梅州","中山","德庆","阳江","云浮","珠海","汕头","佛山"});
        model.put("广西", new String[]{"南宁","桂林","阳朔","柳州","梧州","玉林","桂平","贺州","钦州","贵港","防城港","百色","北海","河池","来宾","崇左"});
        model.put("云南", new String[]{"昆明","保山","楚雄","德宏","红河","临沧","怒江","曲靖","思茅","文山","玉溪","昭通","丽江","大理"});
        model.put("海南", new String[]{"海口","三亚","儋州","琼山","通什","文昌"});
        model.put("新疆", new String[]{"乌鲁木齐","阿勒泰","阿克苏","昌吉","哈密","和田","喀什","克拉玛依","石河子","塔城","库尔勒","吐鲁番","伊宁"});
    }
}

2. Define the method of obtaining provinces, create a Map collection, assign the mapping collection obtained in the previous step to it, and use the keySet() method of the Map collection to obtain the items in the collection. The Set collection composed of all key objects is the province collection. Create a one-dimensional array of Object type, use the toArray() method of the Set interface to convert the Set collection into an array, and return this array as the parameter of the province selection drop-down list.

3. Use the setModel() method of the JComboBox class to add province information to the province drop-down list. The parameter is the method to get the province in the previous step.

4. Define the method of obtaining cities/counties based on provinces, create a Map collection, assign the mapping collection obtained in step 1 to it, and use the get() method of the Map collection to obtain the value of the specified key, that is For the city/county collection, create a one-dimensional array of String[] type and assign the city/county collection to the array.

5. Define the option status change event of the province drop-down list. In this event, obtain the selected province through the getSelectedItem() method of the JComboBox class. The default is the first value in the province collection, and then use the JComboBox class The removeAllItems() method clears the city/county list, obtains the city/county array based on the selected province, and finally uses the setModel() method of JComboBox to re-add the value of the city/county list.

import java.awt.Graphics;
import java.awt.Image;
 
import javax.swing.JPanel;
 
/**
 * 带背景的面板组件
 *
 * @author ZhongWei Lee
 */
public class BackgroundPanel extends JPanel {
 
    /**
     *
     */
    private static final long serialVersionUID = 7758689434195492602L;
    /**
     * 背景图片
     */
    private Image image;
 
    /**
     * 构造方法
     */
    public BackgroundPanel() {
        super();
        setOpaque(false);
        setLayout(null);
    }
 
    /**
     * 设置图片的方法
     */
    public void setImage(Image image) {
        this.image = image;
    }
 
    @Override
    protected void paintComponent(Graphics g) {// 重写绘制组件外观
        if (image != null) {
            int width = getWidth();// 获取组件大小
            int height = getHeight();
            g.drawImage(image, 0, 0, width, height, this);// 绘制图片与组件大小相同
        }
        super.paintComponent(g);// 执行超类方法
    }
}

  import java.awt.Image;
import java.awt.Toolkit;
import java.io.BufferedInputStream;
import java.io.ByteArrayOutputStream;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.util.HashMap;
import java.util.Iterator;
import javax.swing.ImageIcon;
 
/**
 * Utility class for managing resources such as colors, fonts, images, etc.
 *
 * This class may be freely distributed as part of any application or plugin.
 * <p>
 * Copyright (c) 2003 - 2004, Instantiations, Inc. <br>All Rights Reserved
 *
 * @author scheglov_ke
 */
public class SwingResourceManager {
     
    /**
     * Maps image names to images
     */
    private static HashMap<String, Image> m_ClassImageMap = new HashMap<String, Image>();
     
    /**
     * Returns an image encoded by the specified input stream
     * @param is InputStream The input stream encoding the image data
     * @return Image The image encoded by the specified input stream
     */
    private static Image getImage(InputStream is) {
        try {
            ByteArrayOutputStream baos = new ByteArrayOutputStream();
            byte buf[] = new byte[1024 * 4];
            while (true) {
                int n = is.read(buf);
                if (n == -1)
                    break;
                baos.write(buf, 0, n);
            }
            baos.close();
            return Toolkit.getDefaultToolkit().createImage(baos.toByteArray());
        } catch (Throwable e) {
            return null;
        }
    }
     
    /**
     * Returns an image stored in the file at the specified path relative to the specified class
     * @param clazz Class The class relative to which to find the image
     * @param path String The path to the image file
     * @return Image The image stored in the file at the specified path
     */
    public static Image getImage(Class<?> clazz, String path) {
        String key = clazz.getName() + '|' + path;
        Image image = m_ClassImageMap.get(key);
        if (image == null) {
            if ((path.length() > 0) && (path.charAt(0) == '/')) {
                String newPath = path.substring(1, path.length());
                image = getImage(new BufferedInputStream(clazz.getClassLoader().getResourceAsStream(newPath)));
            } else {
                image = getImage(clazz.getResourceAsStream(path));
            }
            m_ClassImageMap.put(key, image);
        }
        return image;
    }
     
    /**
     * Returns an image stored in the file at the specified path
     * @param path String The path to the image file
     * @return Image The image stored in the file at the specified path
     */
    public static Image getImage(String path) {
        return getImage("default", path); //$NON-NLS-1$
    }
     
    /**
     * Returns an image stored in the file at the specified path
     * @param section String The storage section in the cache
     * @param path String The path to the image file
     * @return Image The image stored in the file at the specified path
     */
    public static Image getImage(String section, String path) {
        String key = section + '|' + SwingResourceManager.class.getName() + '|' + path;
        Image image = m_ClassImageMap.get(key);
        if (image == null) {
            try {
                FileInputStream fis = new FileInputStream(path);
                image = getImage(fis);
                m_ClassImageMap.put(key, image);
                fis.close();
            } catch (IOException e) {
                return null;
            }
        }
        return image;
    }
     
    /**
     * Clear cached images in specified section
     * @param section the section do clear
     */
    public static void clearImages(String section) {
        for (Iterator<String> I = m_ClassImageMap.keySet().iterator(); I.hasNext();) {
            String key = I.next();
            if (!key.startsWith(section + '|'))
                continue;
            Image image = m_ClassImageMap.get(key);
            image.flush();
            I.remove();
        }
    }
     
    /**
     * Returns an icon stored in the file at the specified path relative to the specified class
     * @param clazz Class The class relative to which to find the icon
     * @param path String The path to the icon file
     * @return Icon The icon stored in the file at the specified path
     */
    public static ImageIcon getIcon(Class<?> clazz, String path) {
        return getIcon(getImage(clazz, path));
    }
     
    /**
     * Returns an icon stored in the file at the specified path
     * @param path String The path to the icon file
     * @return Icon The icon stored in the file at the specified path
     */
    public static ImageIcon getIcon(String path) {
        return getIcon("default", path); //$NON-NLS-1$
    }
     
    /**
     * Returns an icon stored in the file at the specified path
     * @param section String The storage section in the cache
     * @param path String The path to the icon file
     * @return Icon The icon stored in the file at the specified path
     */
    public static ImageIcon getIcon(String section, String path) {
        return getIcon(getImage(section, path));
    }
 
    /**
     * Returns an icon based on the specified image
     * @param image Image The original image
     * @return Icon The icon based on the image
     */
    public static ImageIcon getIcon(Image image) {
        if (image == null)
            return null;
        return new ImageIcon(image);
    }
}

  import java.awt.EventQueue;
import java.awt.event.ItemEvent;
import java.awt.event.ItemListener;
import java.util.Map;
import java.util.Set;
 
import javax.swing.DefaultComboBoxModel;
import javax.swing.JButton;
import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JTextField;
import javax.swing.SwingConstants;
import javax.swing.UIManager;
import javax.swing.border.TitledBorder;
 
 
public class MainFrame extends JFrame {
 
    /**
     *
     */
    private static final long serialVersionUID = -4595347311922711984L;
    private JTextField textField_3;
    private JTextField textField_1;
    private JComboBox comboBox_1;
    private JTextField textField;
    private JComboBox cityComboBox;
    private JComboBox comboBox;
 
    /**
     * Launch the application
     *
     * @param args
     */
    public static void main(String args[]) {
        EventQueue.invokeLater(new Runnable() {
            public void run() {
                try {
                    UIManager.setLookAndFeel("com.sun.java.swing.plaf.nimbus.NimbusLookAndFeel");
                    MainFrame frame = new MainFrame();
                    frame.setVisible(true);
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        });
    }
 
    /**
     * Create the frame
     */
    public MainFrame() {
        getContentPane().setLayout(null);
        setBounds(100, 100, 518, 379);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        //获取默认的市/县
        String province=(String)getProvince()[0];
        setTitle("输入指定省/直辖市查询对应的市县");
 
        final BackgroundPanel backgroundPanel = new BackgroundPanel();
        backgroundPanel.setImage(SwingResourceManager.getImage(MainFrame.class, "/images/background.jpg"));
        backgroundPanel.setBounds(0, 0, 510, 380);
        getContentPane().add(backgroundPanel);
 
        final JPanel panel = new JPanel();
        panel.setOpaque(false);
        panel.setBounds(36, 126, 438, 70);
        backgroundPanel.add(panel);
        panel.setLayout(null);
        panel.setBorder(new TitledBorder(null, "居住地", TitledBorder.DEFAULT_JUSTIFICATION, TitledBorder.DEFAULT_POSITION, null, null));
        cityComboBox = new JComboBox();
        cityComboBox.setBounds(245, 25, 124, 27);
        panel.add(cityComboBox);
         
        cityComboBox.setModel(new DefaultComboBoxModel(getCity(province)));
 
        comboBox = new JComboBox();
        comboBox.setBounds(25, 25, 124, 27);
        panel.add(comboBox);
        comboBox.addItemListener(new ItemListener() {
            public void itemStateChanged(final ItemEvent e) { // 选项状态更改事件
                itemChange();
            }
        });
        comboBox.setModel(new DefaultComboBoxModel(getProvince())); // 添加省份信息
 
        final JLabel label = new JLabel();
        label.setText("省/直辖市");
        label.setBounds(155, 30, 66, 18);
        panel.add(label);
 
        final JLabel label_1 = new JLabel();
        label_1.setText("市/县");
        label_1.setBounds(375, 30, 37, 18);
        panel.add(label_1);
 
        final JLabel label_2 = new JLabel();
        label_2.setBounds(36, 43, 65, 18);
        backgroundPanel.add(label_2);
        label_2.setHorizontalAlignment(SwingConstants.RIGHT);
        label_2.setHorizontalTextPosition(SwingConstants.LEADING);
        label_2.setText("姓    名：");
 
        textField = new JTextField();
        textField.setBounds(113, 38, 154, 28);
        backgroundPanel.add(textField);
 
        final JLabel label_3 = new JLabel();
        label_3.setBounds(36, 84, 65, 18);
        backgroundPanel.add(label_3);
        label_3.setHorizontalAlignment(SwingConstants.RIGHT);
        label_3.setHorizontalTextPosition(SwingConstants.LEADING);
        label_3.setText("性    别：");
 
        comboBox_1 = new JComboBox();
        comboBox_1.setBounds(113, 81, 66, 25);
        backgroundPanel.add(comboBox_1);
        comboBox_1.setModel(new DefaultComboBoxModel(new String[] {"男", "女"}));
 
        final JLabel label_4 = new JLabel();
        label_4.setBounds(36, 212, 65, 18);
        backgroundPanel.add(label_4);
        label_4.setHorizontalAlignment(SwingConstants.RIGHT);
        label_4.setHorizontalTextPosition(SwingConstants.LEADING);
        label_4.setText("详细地址：");
 
        textField_1 = new JTextField();
        textField_1.setBounds(113, 208, 367, 28);
        backgroundPanel.add(textField_1);
 
        final JLabel label_4_1 = new JLabel();
        label_4_1.setBounds(36, 252, 65, 18);
        backgroundPanel.add(label_4_1);
        label_4_1.setHorizontalTextPosition(SwingConstants.LEADING);
        label_4_1.setHorizontalAlignment(SwingConstants.RIGHT);
        label_4_1.setText("E-mail：");
 
        textField_3 = new JTextField();
        textField_3.setBounds(113, 248, 367, 27);
        backgroundPanel.add(textField_3);
 
        final JButton button = new JButton();
        button.setBounds(159, 289, 75, 28);
        backgroundPanel.add(button);
        button.setText("保存");
 
        final JButton button_1 = new JButton();
        button_1.setBounds(265, 289, 75, 28);
        backgroundPanel.add(button_1);
        button_1.setText("重置");
        //
    }
 
    /**
     * 获取省、直辖市，自治区
     *
     * @return
     */
    public Object[] getProvince() {
        Map<String, String[]> map = CityMap.model;// 获取省份信息保存到Map中
        Set<String> set = map.keySet(); // 获取Map集合中的键，并以Set集合返回
        Object[] province = set.toArray(); // 转换为数组
        return province; // 返回获取的省份信息
    }
 
    /**
     * 获取指定省对应的市/县
     *
     * @param selectProvince
     * @return
     */
    public String[] getCity(String selectProvince) {
        Map<String, String[]> map = CityMap.model; // 获取省份信息保存到Map中
        String[] arrCity = map.get(selectProvince); // 获取指定键的值
        return arrCity; // 返回获取的市/县
    }
 
    private void itemChange() {
        String selectProvince = (String) comboBox.getSelectedItem();
        cityComboBox.removeAllItems(); // 清空市/县列表
        String[] arrCity = getCity(selectProvince); // 获取市/县
        cityComboBox.setModel(new DefaultComboBoxModel(arrCity)); // 重新添加市/县列表的值
    }
 
}

The effect is as shown:

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