Can we sort HashMap by values?

Can we sort HashMap by values?

In Java, sorting HashMap by values is complicated because there is no direct method available. If we need to sort the HashMap by values, we should create a Comparator. It compares two elements based on the values. After that get the Set of elements from the Map and convert Set into the List.

Can you sort a Hashtable?

Before moving forward, we need to understand that it is not possible to sort a Hashtable since the data is stored by the hashcode of the key, not by the index . So to sort the data of a Hashtable, we need to have a sortable object like an array or an ArrayList. Sorting has to be done on Key or Value.

How will you sort HashMap with one single object?

You can't sort a HashMap , but you can sort its entries obtained with entrySet() . After sorting you can put back your entries in a map that supports ordering, for example LinkedHashMap.

Can we get key from value in HashMap?

If your hashmap contain unique key to unique value mapping, you can maintain one more hashmap that contain mapping from Value to Key. In that case you can use second hashmap to get key. Iterate through the entrySet() and to find the keys which match the value.

Why HashMap is used in Java?

Maps are used for when you want to associate a key with a value and Lists are an ordered collection. ... HashMap are efficient for locating a value based on a key and inserting and deleting values based on a key. The entries of a HashMap are not ordered. ArrayList and LinkedList are an implementation of the List interface.

Which is faster HashMap or ArrayList?

While the HashMap will be slower at first and take more memory, it will be faster for large values of n. The reason the ArrayList has O(n) performance is that every item must be checked for every insertion to make sure it is not already in the list.

What is difference between HashMap and ArrayList?

The difference between ArrayList and HashMap is that ArrayList is an index-based data-structure supported by array, while the HashMap is a mapped data structure, which works on hashing to retrieve stored values. Although both are used to store objects, they are different in their implementation, function, and usage.

What is difference between HashSet and HashMap?

Hashmap is the implementation of Map interface. Hashset on other hand is the implementation of set interface. Hashmap internally do not implements hashset or any set for its implementation. Hashset internally uses Hashmap for its implementation.

Which is faster HashSet or HashMap?

HashMap is faster/ than HashSet because values are associated with a unique key. HashSet is slower than HashMap because the member object is used for calculating hashcode value, which can be same for two objects.

Does HashMap allow duplicates?

HashMap does not allow duplicate keys however it allows to have duplicate values. HashSet permits to have a single null value. HashMap permits single null key and any number of null values.

Why HashMap is fast?

HashMap is faster than HashSet because the values are associated to a unique key. In HashSet , member object is used for calculating hashcode value which can be same for two objects so equals() method is used to check for equality. If it returns false , that means the two objects are different.

Will TreeMap allow duplicates?

A TreeMap cannot contain duplicate keys. TreeMap cannot contain the null key. However, It can have null values.

What is difference between TreeMap and HashMap?

HashMap allows a single null key and multiple null values. TreeMap does not allow null keys but can have multiple null values. HashMap allows heterogeneous elements because it does not perform sorting on keys. TreeMap allows homogeneous values as a key because of sorting.

What are similarities and differences between ArrayList and vector?

ArrayList is non-synchronized. Vector is synchronized. ArrayList increments 50% of its current size if element added exceeds its capacity. Vector increments 100% of its current size if element added exceeds its capacity.