**Contents**show

## How does HashMap differs from Java 7 & 8?

2 Answers. In Java 7 after calculating hash from hash function if more then one element has same hash than they are searched by linear search so it’s complexity is (n). In Java 8 that search is performed by binary search so the complexity will become **log(n)**.

## What is K and V in HashMap?

**value put**(Key k, Value v): Inserts key value mapping into the map. Used in the above example. int size(): Returns the size of the map – Number of key-value mappings. Collection values(): It returns a collection of values of map. Value remove(Object key): It removes the key-value pair for the specified key.

## Why HashMap get is O 1?

To be very precise, **The amortized/average case performance of Hashmap** is said to be O(1) for put and get operation. Remember, hashmap’s get and put operation takes O(1) time only in case of good hashcode implementation which distributes items across buckets.

## Is a HashMap efficient?

HashMap, being a hashtable-based implementation, internally uses an array-based data structure to organize its elements according to the hash function. HashMap provides expected constant-time performance O(1) for most operations like add(), remove() and contains(). Therefore, it’s **significantly faster than a TreeMap**.

## What is Treeify_threshold?

In Java 8, HashMap replaces the linked list with another useful data structure i.e. **binary tree on breaching a certain threshold**, which is known as TREEIFY_THRESHOLD . Once this threshold is reached the linked list of Entries is converted to the TreeNodes which reduces the time complexity from O(n) to O(log(n)) .

## Is HashMap thread safe?

HashMap is non-synchronized. It **is not thread-safe** and can’t be shared between many threads without proper synchronization code whereas Hashtable is synchronized.

## Why HashMap is called HashMap?

HashMap is known as HashMap because **it uses a technique called Hashing**. Hashing is a technique of converting a large String to small String that represents the same String. A shorter value helps in indexing and faster searches. HashSet also uses HashMap internally.

## Can we iterate HashMap?

There is a numerous number of ways to iterate over HashMap of which 5 are listed as below: **Iterate through a HashMap EntrySet using Iterators**. Iterate through HashMap KeySet using Iterator. Iterate HashMap using for-each loop.

## Are dictionaries O 1?

If a dictionary/map is implemented as a HashMap , it has a best **case complexity** of O(1) , since i best case it requires exactly the calculation of the hash-code of the key element for retrieval, if there are no key collisions.

## What is the difference between HashMap and HashSet?

Basically, Map Interface has two implementation classes HashMap and TreeMap the main difference is TreeMap maintains an order of the objects but **HashMap will not**. HashMap allows null values and null keys. Both HashSet and HashMap are not synchronized.

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Difference between HashMap and HashSet.

Basic | HashSet | HashMap |
---|---|---|

Insertion Method | Add() | Put() |

## Does HashMap maintain insertion order?

**HashMap does not maintains insertion order** in java. Hashtable does not maintains insertion order in java. LinkedHashMap maintains insertion order in java.

## When HashMap increase its size?

As soon as 13^{th} element (key-value pair) will come into the Hashmap, it will increase its size from default 2^{4} = 16 buckets to 2^{5} = 32 buckets. Another way to calculate size: **When the load factor ratio (m/n) reaches 0.75 at** that time, hashmap increases its capacity.

## How does hashCode work in HashMap?

In HashMap, hashCode() is **used to calculate the bucket and therefore calculate the index**. equals method is used to check that 2 objects are equal or not. … HashMap uses equals() to compare the key whether the are equal or not. If equals() method return true, they are equal otherwise not equal.