Storing and Retrieving ArrayList values from hashmap

Question

I have a hashmap of the following type

HashMap<String,ArrayList<Integer>> map=new HashMap<String,ArrayList<Integer>>();     

The values stored are like this :

mango | 0,4,8,9,12 apple | 2,3 grapes| 1,7 peach | 5,6,11 

I want to store as well as fetch those Integers using Iterator or any other way with minimum lines of code.How can I do it?

EDIT 1

The numbers are added at random (not together) as key is matched to the appropriate line.

EDIT 2

How can I point to the arraylist while adding ?

I am getting error while adding a new number 18 in the line map.put(string,number);

Answer 1

Our variable:

Map<String, List<Integer>> map = new HashMap<String, List<Integer>>(); 

To store:

map.put("mango", new ArrayList<Integer>(Arrays.asList(0, 4, 8, 9, 12))); 

To add numbers one and one, you can do something like this:

String key = "mango"; int number = 42; if (map.get(key) == null) {     map.put(key, new ArrayList<Integer>()); } map.get(key).add(number); 

In Java 8 you can use putIfAbsent to add the list if it did not exist already:

map.putIfAbsent(key, new ArrayList<Integer>()); map.get(key).add(number); 

---

Use the map.entrySet() method to iterate on:

for (Entry<String, List<Integer>> ee : map.entrySet()) {     String key = ee.getKey();     List<Integer> values = ee.getValue();     // TODO: Do something. } 

Answer 2

Iterator it = map.entrySet().iterator(); while (it.hasNext()) {      Map.Entry pairs = (Map.Entry)it.next();       if(pairs.getKey().equals("mango"))      {         map.put(pairs.getKey(), pairs.getValue().add(18));      }       else if(!map.containsKey("mango"))      {         List<Integer> ints = new ArrayList<Integer>();         ints.add(18);         map.put("mango",ints);      }       it.remove(); // avoids a ConcurrentModificationException } 

EDIT: So inside the while try this:

map.put(pairs.getKey(), pairs.getValue().add(number)) 

You are getting the error because you are trying to put an integer to the values, whereas it is expected an ArrayList.

EDIT 2: Then put the following inside your while loop:

if(pairs.getKey().equals("mango")) {     map.put(pairs.getKey(), pairs.getValue().add(18)); }  else if(!map.containsKey("mango")) {      List<Integer> ints = new ArrayList<Integer>();      ints.add(18);      map.put("mango",ints);  } 

EDIT 3: By reading your requirements, I come to think you may not need a loop. You may want to only check if the map contains the key mango, and if it does add 18, else create a new entry in the map with key mango and value 18.

So all you may need is the following, without the loop:

if(map.containsKey("mango")) {     map.put("mango", map.get("mango).add(18)); }  else {     List<Integer> ints = new ArrayList<Integer>();     ints.add(18);     map.put("mango", ints); }