java HashMap 元素到 Array 的 ArrayList
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ArrayList of HashMap elements to Array
提问by Medeiros
How can I get an array of elements in a ArrayListof HashMaps? I have an HashMap with url key on it. The value is a url address. Several HashMapsare stored in a ArrayList. What I want is an arraywith all url strings. I'm not happy with the solution I found because I think it could be extracted from ArrayListwith some manipulation.
如何获取 a ArrayListof 中的元素数组HashMaps？我有一个带有 url 键的 HashMap。该值是一个 url 地址。有几个HashMaps存储在一个ArrayList. 我想要的是array包含所有 url 字符串的。我对找到的解决方案不满意，因为我认为可以通过ArrayList一些操作来提取它。
// Hashmap for ListView
ArrayList<HashMap<String, String>> itemsList = new ArrayList<HashMap<String, String>>();
// Creating JSON Parser instance
JSONParser jParser = new JSONParser();
jParser.execute(url);
try {
JSONObject json = jParser.get();
items = json.getJSONArray(TAG_ITEMS);
//This is the solution that I want to optimize
urls = new String[items.length()];
// looping through All items
for(int i = 0; i < items.length(); i++){
JSONObject c = items.getJSONObject(i);
// Storing each json item in variable
String title = c.getString(TAG_TITLE);
String description = c.getString(TAG_DESCRIPTION);
String author = c.getString(TAG_AUTHOR);
// Media is another JSONObject
JSONObject m = c.getJSONObject(TAG_MEDIA);
String url = m.getString(TAG_URL);
// creating new HashMap
HashMap<String, String> map = new HashMap<String, String>();
// adding each child node to HashMap key => value
map.put(TAG_TITLE, title);
map.put(TAG_DESCRIPTION, description);
map.put(TAG_AUTHOR, author);
map.put(TAG_URL, url);
// Solution
urls[i] = url;
// adding HashList to ArrayList
itemsList.add(map);
}
} catch (JSONException e) {
e.printStackTrace();
} catch (InterruptedException e) {
e.printStackTrace();
} catch (ExecutionException e) {
e.printStackTrace();
}
回答by Cooper
From what I can deduce from your question, it sounds like you're trying to do the following
根据我从您的问题中推断出的，听起来您正在尝试执行以下操作
// Assuming previously declared and instantiated urls ArrayList with populated values in the nested HashMaps.
ArrayList<HashMap<String, String>> urls;
// Create a new List using HashMap.values from urls.
List<String> urlList = new ArrayList<String>(urls.get(index).values());
urls.get(index).values()will return a Collectionview of the values contained in the HashMapat the specified ArrayListindex, which will be used to instantiate and populate a new ArrayList.
urls.get(index).values()将返回Collection包含在HashMap指定ArrayList索引处的值的视图，该视图将用于实例化和填充新的ArrayList.
If you want to obtain allof the values within eachof the nested HashMapsor urls, you can do so in a similar manner, but you will need to iterate through the entire urls ArrayList
如果您想获取每个嵌套or 中的所有值，您可以以类似的方式进行，但您需要遍历整个HashMapsurlsurls ArrayList
for (HashMap<String, String> urlValues : urls) {
urlList.addAll(urlValues.values());
}
P.S. Forgive my bad variable names!
PS 原谅我糟糕的变量名！
回答by CaTalyst.X
It looks like you are building a table. If you can add the Google Guava Library, you could just use the following:
看起来您正在构建一张桌子。如果你可以添加谷歌番石榴库，你可以只使用以下内容：
Table<Integer, String, String> Table = HashedBasedTable.create()
See the JavaDoc:
请参阅 JavaDoc：
http://docs.guava-libraries.googlecode.com/git/javadoc/com/google/common/collect/Table.html
http://docs.guava-libraries.googlecode.com/git/javadoc/com/google/common/collect/Table.html
