如何从Arraylist中获取字符串？

Question

I have a Globals.mylist=new arraylist<hashmap<String,String>> mylist, and hashmap map1 to keep my product order before I insert them into database. this part was when I insert my product order into Globals.mylist :

if (Globals.mylist == null) { 
    Globals.mylist = new ArrayList<HashMap<String, String>>();
}
id = bun.getLong("id");
Id=String.valueOf(id);
brand = bun.getString("brand");
type = bun.getString("type");
qty = bun.getString("qty");
if (Globals.mylist.size() == 0) {
  map1.put("one", Id);
  map1.put("two", brand);
  map1.put("three", type);
  map1.put("four", qty); 
  Globals.mylist.add(map1);
} else {
  int j = Globals.mylist.size();
  map1.put("one", Id);
  map1.put("two", brand);
  map1.put("three", type);
  map1.put("four", qty); 
  Globals.mylist.add(j,map1);
}

And this part was when I try to get string from Globals.mylist into sqlite

for (int i=0; i<Globals.mylist.size();i++) {
map1=Globals.mylist.get(i);
map1.get(Id);
map1.get(qty);
orderdtl = dataSource.createorderdtl(orderid, Id, qty);
}

But I get an error. It tells me that Id=0 and qty=null . I try to search reference, but I cant implement them. How can I get string id and string qty from Globals.mylist to inserted into sqlite.

Answer 1

To retrieve a value from a Map you need it's key.

Previously in your code, you generated the map using...

map1.put("one", Id);
map1.put("two", brand);
map1.put("three", type);
map1.put("four", qty); 

Which gives you the keys. To retreieve the values, you would need to use the appropriate key, for example...

map1=Globals.mylist.get(i);
String id = map1.get("one");
String qty = map1.get("four");

You might like to take a look through The Map Interface for more details

Answer 2

使用LinkedHashMap可以简化插入顺序的设计，它会容易得多。

Answer 3

Firstly, I don't think we have enough code. But the .get(int) function returns an object, it doesn't actually do anything so you'll need to do something like System.out.println(map1.get(Id)).

Answer 4

Your problem is that you are trying to get the value of the Map using its value which is not the way it is implemented.

map1.get(Id);
map1.get(qty);

Not the right way.

---

You need to call Map#get on the key whose value you need to retrieve. You will get the value of type String as you have declared it so retrieve it in the variable of the same type.

String Id = map1.get("one");
String qty = map1.get("four");

The right way to call it.

Answer 5

While adding something to map, you use key value pair.

map.put(key, value);

when you want to get string you should use;

map.get(key);