实例059 - Map映射集合实现省市级联选择框

心法领悟059：掌握各种Map集合。

Map集合的具体实现有很多，应该根据需要来选择。其中HashMap是最常用的映射集合，它只允许一条记录的键为null，但是却不限制集合中值为null的数量。HashTable实现了一个映射，它不允许任何键值为空，TreeMap集合将对集合中的键值排序，默认排序方式为升序。

   public static Map<String,String[]> model=new LinkedHashMap();
    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"});
//.....


	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
	}
	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
    }