java map实现二级联动查询（省市区下拉列表查询）

1.Map集合可以保存键值映射关系，这非常适合本实例所需要的数据结构，所有省份信息可以保存为Map集合的键，而每个键可以保存对应的城市信息，本实例就是利用Map集合实现了省市级联选择框，当选择省份信息时，将改变城市下拉选择框对应的内容。
思路分析：
1. 创建全国（省，直辖市，自治区）映射集合，即LinkedHashMap对象，使用Map接口的put()方法向集合中添加指定的省与城市的映射关系，其中值为String型一维数组。
代码如下：
CityMap.java
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. 定义获取省份的方法，创建一个Map集合，将上一步得到的映射集合赋值给它，使用Map集合的keySet()方法获取该集合中的所有键对象组成的Set集合，即为省分集合，创建一个Object型一维数组，使用Set接口的toArray()方法将Set集合转换为数组，返回此数组作为省份选择下拉列表的参数。
3. 使用JComboBox类的setModel()方法为省份下拉列表添加省份信息，参数即为上一步中的获取省份方法。
4. 定义根据省份获取市/县的方法，创建一个Map集合，将步骤1中得到的映射集合赋值给它，使用Map集合的get()方法获取指定键的值，即为市/县集合，创建一个String[]型一维数组，将市/县集合赋值给该数组。
5. 定义省份下拉列表的选项状态更改事件，在该事件中通过JComboBox类的getSelectedItem()方法获取选中的省份，默认为省份集合中的第一个值，然后使用JComboBox类的removeAllItems()方法清空市/县列表，根据选中的省份获取市/县数组，最后使用JComboBox的setModel()方法重新添加市/县列表的值。