Hashmap is also known as Hash table. It is a data structure that matches keys to values. It preserves these match pairs. It helps to carry out a fixed abstract data type. HashMap is used in the Programming paradigm.There are two ways HashMap can be sorted using Java. HashMap is to be sorted. let us know more about that the Sort Hashmap-Know More.
Sorting HashMap is based on values and keys. HashMap is simple to use in solving many problems in software engineering. To solve these problems, the user of HashMap should first understand the use cases of the hashtable. A Hash table uses a hash code to compute an index into a series of slots from where the required value is located. Every single key is attached to a specific bucket. Although sometimes collisions can occur as a result of the imperfect hash function. This causes one index to be generated over one key.
In this article, we clearly explained all you need to know.
Sorting of HashMap
Two Important ways are necessary to sort HashMap. They include sorting by keys and values. Nonetheless, these ways are only effective when there is a grounded understanding of the internal workings.
Let’s examine them.
Internal Workings
The following steps can be followed
- The computation of hashcode for each key to be inserted.
- The hashcode can be employed to identify the specific bucket for the critical storage.
- Check for the presence of a list of corresponding nodes to the bucket.
- Once the List is available, create a new node which should be attached to the end of the List. However, a new list should be created if the first List is not accessible.
- Check for keys in the list entries that match the key.
- If a match exists, the value is overridden, and a new entry is added to the List.
With a break in the flow of adequate information, uncertainty on what next step to take arises. Although, when selecting what data structure to implement, one needs to consider what they need it for. HashMaps are not created explicitly for sorting – but they are for easy retrieval. So, when carrying this out, the user has to extract every element from the hashmap and place them into a data structure highly suitable for sortings, such as a set or a heap, and then sort them there.
Let’s look at the different ways of sorting.
1. Sorting HashMap by Keys
Sorting by keys can be done in two ways:
– Using LinkedHashMap
– Using TreeMap
A. Process using LinkedHashMap
The first thing to know is that the key-value pairs are not In any particular order, and they aře to be sorted based on their value. This type of sorting is done in the following steps:
– Obtain set keys.
– Then, convert them into a list.
– Once converted, the List should be sorted.
– After sorting, copy the List into LinkedHashMap.
B. Process Using TreeMap
Based on their values, a custom comparator compares all key-value pairs. This is done by following four simple steps.
– Using Java, create a TreeMap with a custom comparator.
– Initiate the comparison based on values and keys
– Collate all key-value pairs and transfer them into the TreeMap
– Return the Treemap.
Is HashMap always mandatory?
If your only interest is in the Map Interface, it is strongly advised to use a TreeMap.
If a person only deems it fit to sort through comparing values, then there happens to be a need for a code to be written. If the only intention is to do it once, then it is ok to sort the values of the HashMap:
Map<String, Person> people = new HashMap<>();
Person jim = new Person(“Jim”, 25);
Person scott = new Person(“Scott”, 28);
Person anna = new Person(“Anna”, 23);
people.put(jim.getName(), jim);
people.put(scott.getName(), scott);
people.put(anna.getName(), anna);
// not yet sorted
List<Person> peopleByAge = new ArrayList<>(people.values());
Collections.sort(peopleByAge, Comparator.comparing(Person::getAge));
for (Person p : peopleByAge) {
System.out.println(p.getName() + “\t” + p.getAge());}
If you want to access this sorted List often, you could insert your elements into a HashMap<TreeSet<Person>>, though the semantics of sets and lists are slightly different.
2. Sorting HashMap by Values
Using a Comparator to Sort HashMap by Value
There is no particular direct method for carrying out this type of sorting. To carry out
In this process, there is a need for the elements to be compared based on the values by using a Comparator.
After using the map, collect the set of elements and convert them into the List. Now, to sort the List, a custom comparator should be used in addition to the Collections sort[List) the method that must be applied sorts these elements by values by passing the comparator.
After then, copy the sorted elements into the new LinkedHashMap, which you create.
These automatically a HashMap with values sorted in order.
Application of Hashing
1. Cache
These supplementary data tables accelerate access to data stored in slower media. Erasing old colliding entries and havìng them replaced with newer ones can help solve collisions that result from two different keys mapped to the exact location.
2. Associative Arrays
HashMaps effectively execute varied types of in-memory tables that carry out associative arrays.
3. Transposition Table
It helps to store information about each previous search section accurately.
4. Database Indexing
HashMaps are used as database indices and data structures that are disk-based.
5. Sets
Set data structure stores particular values in no specific order. A value’s membership in a sample is tested using a set. Set is not mainly used for retrieval of element(s).
Advantages Of Hashing
Speed is one of the significant merits of hashing. It offers access to an element in the record time which becomes more effective when the number of entries is ascertained ahead of time.
Conclusion
Sorting HashMap is carried out in two relatively accurate methods. It brings order and assigns particular keys to specific values.
Frequently Asked Questions
1 What Properties Must A Good Hash Function Have?
Imperfect hash functions can cause collisions, described as when two identical keys are mapped to the same place. A hash function must be uniform, deterministic, and not expensive to reduce collisions.
2 Does HashMap Sort Values?
Well, HashMap sorts according to values. It sorts based on values. It is carried out this way: A list is used to store the first set of entries. Keys and values are then obtained from the List and put in a new hashmap.
3 Can HashMap Be Sorted In Descending Order?
Sorting HashMap in descending order is possible. Using collections, one can reverse the order of comparators.
4 Is HashSet Sorted In Java?
It is not possible to sort HashSet in Java. Although, this can be done indirectly by converting the HashSet elements into TreeSet or List. This helps to keep the elements in the target type.
