Java之HashMap.values()转List时的错误和正确演示

List<AreaItemOpt> areaItemOpts = (List<AreaItemOpt>) areaItemOptMap.values();
return areaItemOpts;

public Collection<V> values() {
      Collection<V> vs = values;
      return (vs != null ? vs : (values = new Values()));
  }

public ArrayList(Collection<? extends E> c) {
        elementData = c.toArray();
        if ((size = elementData.length) != 0) {
            // c.toArray might (incorrectly) not return Object[] (see 6260652)
            if (elementData.getClass() != Object[].class)
                elementData = Arrays.copyOf(elementData, size, Object[].class);
        } else {
            // replace with empty array.
            this.elementData = EMPTY_ELEMENTDATA;
        }
    }

List<AreaItemOpt> areaItemOpts = new ArrayList<>(areaItemOptMap.values());
return areaItemOpts;

 List<T> list=(List<T>) Arrays.asList(map.values().toArray());//先转数组再转list

public class Map转List {
    public static void main(String[] args) {
        //开辟空间
        HashMap<Integer,String> hashMap = new HashMap<Integer,String>();
        //存入数据
        hashMap.put(1,"张三");
        hashMap.put(2,"李四");
        hashMap.put(3,"王五");
        //使用Collection类型接收HashMap的Value值
        Collection<String> collection = hashMap.values();
        //把Collection对象作为参数传入ArrayList构造方法完成类型转换
        ArrayList<String> arrayList = new ArrayList<String>(collection);
        //输出测试
        System.out.println(arrayList.toString());
    }
}