how to convert list into map in java

Question

I have arrayList

List<String> li= new ArrayList<String>() ;
li.add("a");
li.add("b");

I want to convert to ArrayList to HashMap Like this

HashMap<String, List<String>> s= new HashMap<String,List<String>>();

Please help me how to convert to HashMap

A map has keys and values. Is your current list your keys or your values? — TangledUpInBlue, Jan 09 '16 at 03:46
Is there more than one Arraylist of strings being stored as values in your HashMap? — TangledUpInBlue, Jan 09 '16 at 03:55
Your key is whatever identifies the value (your ArrayList, in this case). That is up to you. — TangledUpInBlue, Jan 09 '16 at 04:00
but how we convert this list to hashmap .tell me if any other option to convert list into map @TangledUpInBlue — Nishant Singh, Jan 09 '16 at 04:02
A HashMap has keys and values. You can put the List into your HashMap as a value (i.e. map.set(key, list)), or use the values in the list as keys, or as values. It seems like you want to do the first. Is that true? — TangledUpInBlue, Jan 09 '16 at 04:04
ya bro that's why i have more confusion plz u provide any link through which i read the collection and i am able to solve my problem or provide me example @TangledUpInBlue — Nishant Singh, Jan 09 '16 at 04:10
https://docs.oracle.com/javase/7/docs/api/java/util/HashMap.html? — TangledUpInBlue, Jan 09 '16 at 04:15
If you have solved your problem, please post it as an answer to your own question so the post will be closed. — hsirkar, Jan 09 '16 at 04:28

score 3 · Answer 1 · edited May 23 '17 at 12:31

3

You need to look at this List<Item> list; Map<Key,Item> map = new HashMap<Key,Item>(); for (Item i : list) map.put(i.getKey(),i);

edited May 23 '17 at 12:31

Community

1
1

answered Jan 09 '16 at 04:16

Rahul Bhawar

450
7
17

but for this first we made the Item class after than we are able to do so. is it correct bro – Nishant Singh Jan 09 '16 at 04:18
It is depend on user needs , You can give String object or any other you want, Please View given link to more details – Rahul Bhawar Jan 09 '16 at 04:23
how plz give the example – Nishant Singh Jan 09 '16 at 04:23
public static void main(String[] args) { List list = new ArrayList(); list.add("a"); list.add("b"); Map map = new HashMap(); int keyCount = 0; for (String i : list) { map.put(keyCount++, i); } System.out.println("Data: "+map); } – Rahul Bhawar Jan 09 '16 at 04:28

score 0 · Answer 2 · answered Jan 09 '16 at 04:48

public static void main(String[] args) {

    String name;
          int  count=0; 
 List<String> li= new ArrayList<String>() ;
    li.add("a");
    li.add("d");
    li.add("b");
    li.add("e");
    Iterator i1 = li.iterator();
    while(i1.hasNext())
            {
        name = (String)i1.next();
        System.out.println(name);
            }

    HashMap <Integer,String> hm = new HashMap<Integer,String>();
    for(String i : li)
    {
    hm.put(count++,i);
    }
    System.out.println("after converting list to map ");
    System.out.println(hm);
}

score 0 · Accepted Answer · answered Jan 09 '16 at 06:06

  final List<String> originalList = Arrays.asList("a","b");
    //JAVA 8
    //Always initialize maps/collections with their Interface
    final Map<Integer, String> mapFromListJavaEight =
            IntStream.range(0,originalList.size())
            .mapToObj(index -> index)
            .collect(Collectors.toMap(Function.identity(),
                    originalList::get));
    // JAVA < 8 & JAVA >= 5
    final Map<Integer, String> mapFromListJavaSeven =
            new HashMap<>();
    for(int i = 0; i < originalList.size(); i++){
        mapFromListJavaSeven.put(i,originalList.get(i));
    }

how to convert list into map in java

3 Answers3