Hashmap implementation

By reading info from file of text, the program saves into hashmap the words and the amount, that they were used in. As a result it prints it into console.

In this project were achieved following objectives:

• Implementaion of a hash table with collisions resolution by chaining.

• Implementation of a mechanism to dynamically expand hash tables.

• Learnining how to use inner classes to improve encapsulation.

• Implementation of an array that dynamically expands.

• Reading a text file and register in which positions appears each word.

Authors

• Daria Melnyk - Initial work - DashulyaMelnyk

Useful theory

Algorithms of hashmap's work 😕

HashMap uses multiple buckets and each bucket points to a Singly Linked List where the entries (nodes) are stored. Once the bucket is identified by the hash function using hashcode, then hashCode is used to check if there is already a key with the same hashCode or not in the bucket(singly linked list).

HashMap expansion 👻

To decide when to increase the number of buckets you should use the concept of the load factor α of the hash table: α = n / m where n is the number of elements contained in the table, and m is the number of available buckets. So we can calculate the maximum number of elements for the hash table to work properly: n = m * α

Reading a file with extention .txt :speech_balloon:

For reading from file was used the object of class BufferReader. The example of usage:

BufferedReader in = new BufferedReader(new FileReader("file.txt"));

To get the information line by line:

String line = in.readLine();

Obtaining the location of the word in line :smirk_cat:

The indexOf() method returns the position of the first occurrence of specified character(s) in a string. Search a string for the first occurrence of "planet":

String myStr = "Hello planet earth, you are a great planet.";  
System.out.println(myStr.indexOf("planet"));

Result: 6

Files processed by the program

The program processes files of txt.extention. File example:

I hate (java) hate hate
it is really good
java hate me

Result example:

me : [(3:11)]  
i : [(1:1)]  
good : [(2:14)]  
is : [(2:4)]  
it : [(2:1)]  
really : [(2:7)]  
java : [(1:8), (3:1)]  
hate : [(1:3), (1:13), (1:18), (3:6)]