CODEWITHSUNDEEP
javaarraysloopsdynamic
Piotr Szczepanik
Piotr Szczepanik

Reputation: 381

Creating List in a loop

Is there any way to create a loop which will be creating new List 

static Map<Integer, List> dataMap = new HashMap<>();
public static void dec_hex() {

        // Map<Integer, Integer> dataMap = new HashMap<>();
        // dataMap.put(0, 0);
        List<Integer> ls2 = new ArrayList<Integer>();
        List<Integer> ls3 = new ArrayList<Integer>();
        List<Integer> ls4 = new ArrayList<Integer>();
        List<Integer> ls5 = new ArrayList<Integer>();
        List<Integer> ls6 = new ArrayList<Integer>();
        List<Integer> ls7 = new ArrayList<Integer>();
        List<Integer> ls8 = new ArrayList<Integer>();
        List<Integer> ls9 = new ArrayList<Integer>();
        List<Integer> ls10 = new ArrayList<Integer>();

        System.out.println("Liczby");
        for (int i = 0; i < 201; i++) {
            String hex = Integer.toHexString(i);
            System.out.println("DEC: " + i + " HEX: " + hex);
            //for (int a = 2; a<11 ; a++){
            if (i % 2 == 0) {
                ls2.add(i);
                //myList.add(i);
                dataMap.put(2, ls2);
            }
            if (i % 3 == 0) {
                ls3.add(i);
                //myList.add(i);
                dataMap.put(3, ls3);
            }

            if (i % 4 == 0) {
                ls4.add(i);
                //myList.add(i);
                dataMap.put(4, ls4);
            }
            if (i % 5 == 0) {
                ls5.add(i);
                //myList.add(i);
                dataMap.put(5, ls5);
            }
            if (i % 6 == 0) {
                ls6.add(i);
                //myList.add(i);
                dataMap.put(6, ls6);
            }
            if (i % 7 == 0) {
                ls7.add(i);
                //myList.add(i);
                dataMap.put(7, ls7);
            }
            if (i % 8 == 0) {
                ls8.add(i);
            //  myList.add(i);
                dataMap.put(8, ls8);
            }
            if (i % 9 == 0) {
                ls9.add(i);
                //myList.add(i);
                dataMap.put(9, ls9);
            }
            if (i % 10 == 0) {
                ls10.add(i);
                //myList.add(i);
                dataMap.put(10, ls10);
            }
        }

        //String list = myList.toString();
        //System.out.println(list);
        dataMap.toString();
        System.out.println(dataMap);

    }

Is there any way to create a loop to check if number is divisible? If I'm going to use this

    for (int a = 2; a<11 ; a++){
 lsa.add(i); // lets say we've got one list
 dataMap.put(a, ls);
}

The program won't work correctly cause the numbers will reapeat, cause I'm using the same lsa array.

Upvotes: 0

Views: 109

Answers (3)

nafas
nafas

Reputation: 5423

you can shorten your by checking if the map contains a key, if not create a new list and add your data :

for (int i = 1; i < 201; i++) {

   for(int j=2;j<11;j++){

      if(i%j==0){

         if(dataMap.containsKey(j){

           dataMap.get(j).add(i);

         }else{

           List<Integer> list = new ArrayList<Integer>();
           list.add(i);
           dataMap.put(j,list);

        }

      }

   }
}

Upvotes: 0

Anjana
Anjana

Reputation: 883

You can create a List of Lists. 

int max = 10;
List<List<String>> listOfLists = new ArrayList<>();
for(int i=0; i<max; i++) {
             //create a new list and add it to listOfLists
    List<String> myList = new ArrayList<>();
    listOfLists.add(myList);
}

Hope this helps. :)

Upvotes: 4

JB Nizet
JB Nizet

Reputation: 691805

Yes, of course. That's what a Map is for: you give it a key, and it gives you back the value.

    Map<Integer, List<Integer>> dataMap = new HashMap<>();
    for (int i = 0; i < 10; i++) {
        dataMap.put(i, new ArrayList<>());
    }       

    for (int i = 0; i < 201; i++) {
        int key = i % 10;
        List<Integer> list = dataMap.get(key);
        list.add(i);
    }

But since your keys are integers from 0 to 9, you could also just use a List<List<Integer>>, instead of the map.

Upvotes: 1

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