But what if the values of two different keys are the same? As per the example given in the problem statement, such a scenario can definitely arise. Whenever we insert an element into the list, the comparator function will compare the new object inserted against the elements and decide whether to swap its position, thus maintaining the desired sorted order.įor our use case, we simply need to compare the values of the keys. 0 → denotes that object1 is greater than object2.The 'compare” method returns three categories of values based on object comparison: Syntax: public int compare ( Object object1, Object object2 ) How a Comparator Works in JavaĪ comparator object is used for comparing two objects of a user-defined class. The advantage of LinkedHashMap is that elements can be accessed in their insertion order, and thus we return a map that will contain all key-value pairs sorted by value. (Read on for details on how a comparator works in Java).įinally, we copy the elements from the sorted list into a LinkedHashMap.

Next, we sort the list and pass a custom comparator to define our way of ordering the elements. We use ArrayList because it’s dynamic, and we do not need to specify the list size at the time of creation. Step 3: Copy the list items into a LinkedHashMapįirst, we copy the key-value pairs present inside the HashMap into an ArrayList. Step 2: Sort the list using any sorting algorithm of choice Step 1: Copy the elements of hashmap into an ArrayList Finally, get the sorted list and convert it back to a map while maintaining its order.Sort the ArrayList based on values present in each key-value pair.So we choose an ArrayList, where each index of the list contains a key-value pair.Hence, we want to save the key-value pairs in a different data structure to sort them based on their value and maintain order. As we know, the key-value pairs stored in a HashMap do not have an order.In the first solution, the key idea is to store each entry of the HashMap in a list and then sort the list and finally store the list elements in a LinkedHashMap. Solution #1: Sorting a HashMap Using a LinkedHashMap We can assume the number of superheroes is at max 106, and all superhero names are unique. If two superheroes have the same strength, we arrange them based on the alphabetical order of their names and hence the above output. For example, let’s say we are given a list of superheroes and their strengths. We are provided a HashMap of key-value pairs, and we are required to sort this HashMap based on its values. The rest of this article is dedicated to solving this problem. It gets tricky when we want to order the key-value pairs of the HashMap based on values. We can also define a custom comparator and assign it to the TreeMap constructor to define our custom ordering of elements. Ordering by key is easy, as Java supports TreeMap, where every key-value pair is inserted into the HashMap by the natural order of keys. Some programming challenges involve ordering elements that are present in a HashMap. Both read and access are O(1) operations. We're just concerned about the speed at which we can read an element and gain access to the value using the element (if it's present in the cache). In caching, we're not concerned with the order of the elements. The behavior of a HashMap can be thought of as a caching mechanism. If a match is found, override the value else, add a new entry to the List. Now, we check if any key present in the entries of the List matches the key.Ħ. If a List is present, we create a new Node and add it to the end of the List otherwise, we create a new list.ĥ. Next, we check if there is a List of nodes present corresponding to the bucket.Ĥ. In the above image, let’s assume the hashcode for IronMan is 002 - it’ll be stored in the second bucket that maintains a pointer to a List, where each node contains a key and its corresponding value.ģ.Using the hashcode, we check in which bucket the key is to be stored. We compute the hashcode for each of the keys being inserted.Ģ.

Java sorted map