How do I sort two ArrayLists and put them in a Map?

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My program calculates the digit sums of all values entered into a text file. The entered values and their according digit sums are stored in two seperate ArrayLists.

Both ArrayLists are combined into a LinkedHashMap in the end which should be ordered by the digit sum in descending order. If you enter multiple values with the same digit sum, it's supposed to order those (and only those) in descending order by their original value, not the digit sum this time (the rest stays the same as before).

How do I achieve this with Comparators?

My lists and the map:

String filePath = args[0];

LineNumberReader br = new LineNumberReader(new FileReader(filePath));
LinkedHashMap<BigInteger, BigInteger> unsortedMap = new LinkedHashMap<BigInteger, BigInteger>();
List<BigInteger> inputList = new ArrayList<>();
List<BigInteger> DSList = new ArrayList<>();

     while (true) {
        String line = br.readLine();
        if (line == null) {

        BigInteger input = new BigInteger(line);


for(int i = 0; i < inputList.size(); i++){
    unsortedMap.put(inputList.get(i), DSList.get(i));

for(BigInteger key : unsortedMap.keySet()){
    System.out.println(new BigDecimal(key).toPlainString() + " (Digit Sum: " + unsortedMap.get(key) + (")"));


public static BigInteger digitSum(BigInteger number) {

        String digits = number.toString();
        int sum = 0;

        for(int i = 0; i < digits.length(); i++) {
            int digit = (int) (digits.charAt(i) - '0');
            sum = sum + digit;

        return BigInteger.valueOf(sum);


Output has to look like this:

x (digit sum: y) x (digit sum: y) ... x = entered value y = digit sum of x

If you need any further information, feel free to ask.

Here is a solution with a simple class and a Comparator

class Values {
    BigInteger number;
    BigInteger digitSum;

    Values(BigInteger number, BigInteger sum) {
        this.number = number;
        this.digitSum = sum;

    public String toString() {
        return number + " (digit sun:" + digitSum + ")";

And then create a list with this class

 List<Values> inputList = new ArrayList<>();

and add objects of Values to the list using the constructor when reading the file

For sorting you can create a Comparator object like this

Comparator<Values> compareSum = (Values v1, Values v2) -> {
   int result = v1.digitSum.compareTo(v2.digitSum);
   return result != 0 ? result : v1.number.compareTo(v2.number);           

and sort your list in descending order


How to Sort Array, ArrayList, String, Map and Set in Java? Edureka, Here you will learn how to sort Array, ArrayList, String, List, Map and Set in Java. It has various features that make it easy! This article will help you unfold int [] arr = { 52 , 12 , 2 , 72 , 4 }; // array of 5 elements. Arrays.sort(arr);. Unsorted ArrayList: [sorting, java, arraylist, in] Sorted ArrayList in Ascending order : [arraylist, in, java, sorting] Moving ahead with sorting in Java article, let’s see how you can sort integers. Let’s try to implement sorting using a different method i.e using Collections.sort() method. Sort ArrayList in Java Using Collections (Integers)

As there are duplicate keys with different values, you cannot use LinkedHashMap or any other Java Map implementations to store the same key with different value.

You can either create your custom Map or use Apache's Common Map Implementations. The following code shows a solution using MultiValueMap and a custom comparator that sorts by key and then by value in descending order:

  MultiValuedMap<BigInteger, BigInteger> unsortedMap = new ArrayListValuedHashMap<>();
     while (true) {
        String line = br.readLine();
        if (line == null) {
        //Use a single map to put both values
        unsortedMap.put(new BigInteger(line), new BigInteger(methods.digitSum(line)));

  //Do the sorting using custom comparator

  List<Map.Entry<BigInteger, BigInteger>> list = new LinkedList<>(unsortedMap.entries());
  // Sort the list
  Collections.sort(list, new Comparator<Map.Entry<BigInteger, BigInteger> >() {
     public int compare(Map.Entry<BigInteger, BigInteger> o1,
                               Map.Entry<BigInteger, BigInteger> o2) {
        int c = o1.getKey().compareTo(o2.getKey());
        if (c==0){
           c = o1.getValue().compareTo(o2.getValue());
        return c * -1; //descending

  //Place the sorted List into another Map that retains the insert order
  Multimap<BigInteger, BigInteger> sortedMap = LinkedHashMultimap.create();
  for (Map.Entry<BigInteger, BigInteger> entry : list) {
    sortedMap.put(entry.getKey(), entry.getValue());

  for(BigInteger key : sortedMap.keySet()){
    for (BigInteger bi: sortedMap.get(key)) {
       System.out.println("x: " + new BigDecimal(key).toPlainString() + " (Digit Sum: " + bi + (")"));

To use the above Maps you should include the apache commons collections dependency


How to sort array, list, map and set in Java, Learn to sort array or collection in Java. we will learn to sort set, list and map of 2. Sort a List. Lists can be sorted in Java using Collections.sort() API. It uses a  The best and most effective a sort a map by keys is to add all map entries in TreeMap object. TreeMap store the entry sets in sorted order by keys. Java sort map by key HashMap<Integer, String> map = new HashMap<> ();

You can refer to below code to sort your map by value in descending order (in case of same values, sort in descending order of keys). In your case, the keys of the map (passed in parameter) are the inputs from text file and respective values in map are the digit sum.

public static LinkedHashMap<BigInteger, BigInteger> sortByValue(LinkedHashMap<BigInteger, BigInteger> hm)
    List<Map.Entry<BigInteger, BigInteger> > list =
            new LinkedList<Map.Entry<BigInteger, BigInteger> >(hm.entrySet());

    Collections.sort(list, new Comparator<Map.Entry<BigInteger, BigInteger> >() {
        public int compare(Map.Entry<BigInteger, BigInteger> o1,
                           Map.Entry<BigInteger, BigInteger> o2)
            // To handle same value case
            if(o1.getValue().compareTo(o2.getValue()) == 0) {
                return (o2.getKey()).compareTo(o1.getKey());

            return (o2.getValue()).compareTo(o1.getValue());

    LinkedHashMap<BigInteger, BigInteger> temp = new LinkedHashMap<BigInteger, BigInteger>();
    for (Map.Entry<BigInteger, BigInteger> aa : list) {
        temp.put(aa.getKey(), aa.getValue());
    return temp;

The compareTo method is called on object o2 rather than object o1 to get the result in descending order. As mentioned in comment of above code snippet, the if condition will handle your requirement of comparing the keys and sort in descending order of keys when the values are same.

The list of Entry objects is sorted as as per your requirement and these sorted Entry objects are added to LinkedHashMap to maintain the insertion order into the map.

Java 2 Primer Plus, Linked List | | Array List | | Vector | | Hash Set | O-| Sorted Set] a collection of values, so you can think of maps as a composite of two collection implementations. Furthermore, it can be initialized with the values contained in another java.util. The sort () method accepts an instance of Comparator implementing class which must be able to compare the elements contained in the arraylist. Internally, the sort () method uses Arrays.sort () method to compare and sort the elements in the list. ArrayList sort () method implementation public void sort (Comparator<? super E> c)

Sun Certified Programmer For Java 6 Scjp, Exam 310-065, Study , As a result we can store an arraylist in this map by commenting the lines marked as 3 and 4 . Option C is incorrect as it will not work if the lines marked as 2 and 3 are A . Elements in a set are sorted and are in their insertion order in List . In this tutorial we have shared the examples of sorting an String ArrayList and Integer ArrayList. Also Read: Sort ArrayList in descending order; Sort ArrayList of Objects using Comparable and Comparator; Example 1: Sorting of ArrayList<String> Here we are sorting the ArrayList of String type. We are doing it by simply calling the Collections

How to sort a Java HashMap by value, entrySet() ) and input them into an ArrayList (has elements of type Map.Entry<​String Entry<String, Integer> , we need to write our own Comparator code to sort the elements: Comparator<Map. linkedMap.put(e.getKey(), e. 1. import java.util.ArrayList;. 2. import java.util.Collections;. 3. import java.util.Comparator;. 4. In this tutorial we will see how to join (or Combine) two ArrayLists in Java.We will be using addAll() method to add both the ArrayLists in one final ArrayList.. Example: In this example we are merging two ArrayLists in one single ArrayList and then displaying the elements of final List.

Difference between ArrayList and HashMap in Java, ArrayList and HashMap are two commonly used collection classes in Java. //​String value stored along with the key value in hash map hmap.put(123, "Test String"); any order, the returned key-values pairs are not sorted in any kind of order. but HashMap doesn't allow duplicate keys (It does allow duplicate values). Implement your own sort that swaps elements in both ArrayLists. Define a new class to hold a word and its pronunciation. Then define a new Comparable that takes two objects of the new class and compares just the words. Before sorting, use the two ArrayLists to populate a HashMap.