一、需求：创建一个ArrayList集合，存储三个元素，每一个元素都是HashMap,每一个HashMap的键和值都是String,并遍历
分析：
ArrayList集合HashMap集合键和值都是StringHashMap作为元素添加到ArrayList中public static void main(String[] args) {
//创建ArrayList集合
ArrayList<HashMap<String,String>> al=new ArrayList<HashMap<String,String>>();
//创建HashMap集合
HashMap<String,String>hm=new HashMap<String,String>();
//添加键值对
hm.put("01","张三");
hm.put("03","王五");
hm.put("02","李四");
//创建HashMap集合
HashMap<String,String>hm1=new HashMap<String,String>();
//添加键值对
hm1.put("05","张");
hm1.put("04","王");
hm1.put("07","李");
//将HashMap放入ArrList中
al.add(hm);
al.add(hm1);
//遍历
for (HashMap<String,String> ss : al) {
//内层依旧是HashMap的遍历方法
Set<String> key = ss.keySet();
for (String key1 : key) {
String value = ss.get(key1);
System.out.println(key1 + "," + value);
}
}
}二、需求：创建一个HashMap集合，存储三个键值对元素，每一个键值对元素的键都是String,值是ArrayList
分析：
HashMap集合，键是String，值是ArrayListArrayList集合并添加元素ArrayList作为值添加到HashMap集合中public class HashMapInculdingArrayLis {
public static void main(String[] args) {
//创建HashMap集合
HashMap<String, ArrayList<String>> hm=new HashMap<String, ArrayList<String>>();
//创建ArrayList集合对象
ArrayList<String> al=new ArrayList<String>();
al.add("张三");
ArrayList<String> al1=new ArrayList<String>();
ArrayList<String> al2=new ArrayList<String>();
al2.add("王五");
al1.add("李四");
hm.put("01",al);
hm.put("02",al1);
hm.put("03",al2);
//遍历
Set<String>keySet =hm.keySet();
for (String key:keySet){
System.out.print(key+",");
ArrayList<String> strings = hm.get(key);
for (String value:strings){
System.out.println(value);
}
}
}
}
