Adding a HashMap to a HashMap as a value

Question

I am trying to add a Key(String), Value(HashMap) to another HashMap. I somehow keep jumbling up the syntax and logic here. How do I do that? I have a kmap here initialized and then I want to add a key which is a string, and a value which is another HashMap<String, List<Integer>>)

These can be seen in the parameters below:

static HashMap<String, HashMap<String, List<Integer>>> kmap = new HashMap<String, HashMap<String, List<Integer>>>();

public synchronized static void AddMapToList_ofMAP_(HashMap<String, List<Integer>> value, String key) {

    if (!kmap.containsKey(key)) {
        kmap.put(key, new HashMap<String, List<Integer>>());
    }
    HashMap<String, List<Integer>> q = kmap.get(key);

    q.put(key, value);
}

what is the problem you are experiencing? Reading the syntax is seems correct — yugo
– yugo, Commented Feb 4, 2016 at 19:53
The value you want to add with q.put( key, value) should be a List<Integer>, because q is a Map<String, List<Integer>>. — Kenney
– Kenney, Commented Feb 4, 2016 at 19:56

Erick G. Hagstrom · Accepted Answer · 2016-02-04 20:09:47Z

1

It's WAY simpler than you're making it seem. You don't need a separate method, just invoke the put(key, value) method on your kmap. Assuming you have a Map<String, List<Integer>> in a variable named value, it's just:

kmap.put(key, value);

That's all. Just one line.

answered Feb 4, 2016 at 20:09

Erick G. Hagstrom

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1 Comment

dedpo Over a year ago

you're right i made it way more complicated then it needed to be. A single put line does what i need it do THANK U

Walshy · Accepted Answer · 2016-02-04 19:57:07Z

In your parameters you have got a HashMap called value. You are then trying to add that to the HashMap inside the HashMap but the value in that needs to be a List of integers.

Fix:

static HashMap<String, HashMap<String, List<Integer>>> kmap = new HashMap<String, HashMap<String, List<Integer>>>();

public synchronized static void AddMapToList_ofMAP_(
       List<Integer> value, String key) {  

    if (!kmap.containsKey(key)) {
        kmap.put(key, new HashMap<String, List<Integer>>());
    }
        HashMap<String, List<Integer>> q = kmap.get(key);

        q.put(key, value);
    }

Also, a possible way to make this better is using an Object. I'm not sure how the code and what your putting in but an object could work.

I'm also seeing you get the HashMap by the key but you also put that key in the HashMap (The one inside), surely you could just have 1 HashMap there.

Nuwan · Accepted Answer · 2016-02-04 20:48:02Z

I'm not sure what exactly you are trying to achieve here. Here's what possibly you may want to do. Feel free to write more test cases and optimize the code. However this will give you a based structure to work on.

public class Stackoverflow {

static HashMap<String, HashMap<String, List<Integer>>> kmap = new HashMap<String, HashMap<String, List<Integer>>>();

public synchronized static void addIntegerToKmap(String kmapKey, String intMapKey, Integer value) {
    if (!kmap.containsKey(kmapKey)) {
        Map<String, List<Integer>> intMap = new HashMap<String, List<Integer>>();

        HashMap<String, List<Integer>> stringListHashMap = new HashMap<String, List<Integer>>();
        List<Integer> integerList = new ArrayList<Integer>();

        integerList.add(value);
        stringListHashMap.put(intMapKey, integerList);
        kmap.put(kmapKey, stringListHashMap);
    }
    else {
        HashMap<String, List<Integer>> stringListHashMap = kmap.get(kmapKey);
        List<Integer> integerList = stringListHashMap.get(intMapKey);
        if (integerList != null && !integerList.isEmpty()) {
            integerList.add(value);
        }
        else {
            integerList = new ArrayList<Integer>();
            integerList.add(value);
            stringListHashMap.put(intMapKey, integerList);
        }
    }
}

public static void main(String args[]) {
    addIntegerToKmap("A", "A1", 1);
    addIntegerToKmap("A", "A1", 2);

    addIntegerToKmap("A", "A2", 12);
    addIntegerToKmap("A", "A2", 22);

    addIntegerToKmap("B", "B1", 1);

    addIntegerToKmap("A", "A1", 3);
}

}

Youssef Lahoud · Accepted Answer · 2016-02-04 20:00:42Z

-1

The logic is not clear but maybe you want this

q.put(key, value.get(key));

instead of this:

q.put(key, value);

answered Feb 4, 2016 at 20:00

Youssef Lahoud

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