Hash Maps

Question 1

What is a Hash Map?

Answer 1

A Hash Map is a data structure that provides fast look-ups and inserts into specific locations, similar to an array, but it does not use integer keys as indexes.

Question 2

How is a Hash Map typically expressed in memory?

Answer 2

A Hash Map is typically expressed as a large array in memory.

Question 3

What types of keys can a Hash Map accept?

Answer 3

A Hash Map can accept a variety of key types, including strings, doubles, dates, and even custom classes.

Question 4

What are the key characteristics of a Hash Map?

Answer 4

The key characteristics of a Hash Map are fast access and overwrite of elements, non-integer keys, and the ability to store key-value pairs.

Question 5

Is recursion involved in the operations of a Hash Map?

Answer 5

No, recursion is not involved in the operations of a Hash Map.

Question 5

What is the approach to implementing a Hash Map?

Answer 5

The approach to implementing a Hash Map involves creating a big array called buckets and writing a hashing function for the non-integer keys.

Question 6

What is the purpose of the hashing function in a Hash Map?

Answer 6

The hashing function in a Hash Map is used to convert non-integer keys into integers for determining the storage location in the array.

Question 7

How is the modulo operator used in a Hash Map?

Answer 7

The modulo operator (%) is used to determine which bucket in the array to look into based on the hashed key.

Question 8

Can collisions occur in a Hash Map?

Answer 8

Yes, collisions can occur in a Hash Map, where two different keys hash to the same index in the array.

Question 9

How does the Java API handle collisions in a Hash Map?

Answer 9

The Java API handles collisions in a Hash Map by using a technique called chaining.

Question 10

What is the advantage of using chaining to handle collisions in a Hash Map?

Answer 10

The advantage of using chaining for collision resolution in a Hash Map is that it can handle an arbitrary number of collisions efficiently.

Question 11

What happens when there are many collisions in a Hash Map?

Answer 11

When there are many collisions in a Hash Map, it can result in degraded performance and increased lookup time.

Question 12

Is it possible for a key to be stored in multiple buckets in a Hash Map?

Answer 12

No, in a Hash Map with chaining, each key is stored in a single bucket, even if there are collisions.

Question 13

How can you retrieve data from a Hash Map?

Answer 13

Data can be retrieved from a Hash Map using the get method.

Question 14

How can you declare your own Hash Map in Java?

Answer 14

In Java, you can declare your own Hash Map using the HashMap class provided by the Java API.

Question 15

What are the requirements for keys and values in a Hash Map?

Answer 15

In a generic Hash Map, both the key and value must be class types.

Question 16

Do you have to write a hash function for a Hash Map?

Answer 16

No, you don’t have to write a hash function for a Hash Map as many hash functions are pre-implemented in the API for common data types such as String, Double, etc.

Question 17

Why would you consider overriding the hashCode method for a class used as a key in a Hash Map?

Answer 17

You might consider overriding the hashCode method for a class used as a key in a Hash Map to achieve a better spread of keys and improve the efficiency of the Hash Map.

Question 18

What is the benefit of adding the hash codes of non-static attributes in the hashCode implementation?

Answer 18

Adding the hash codes of non-static attributes in the hashCode implementation can help improve the uniqueness and spread of keys in a Hash Map.