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README.md

Store Lab

  • Purpose - to understand HashMap, objects and data encapsulation.

  • Objective - A map/associative array is a data type that allow users to search for a value. The objective of this lab is to understand how to create map and see how we store data affects how its performance.

Part 1 - Equals & HashCode

By default, every Java object has an equals and a hashCode method. Java uses the object's address to calculate the hashCode. By default, two objects are equal if they have the same address. We don't want this. Two objects are equal if they are the same class and have the same values. Your task is to add the equals and hashCode to the User and Cart class.

  1. User
    1. Add an equals method to the User class. The equal method should return true only if the id and name are the same. It return false otherwise.
    2. Add a hashCode method by calling Objects.hash() and gives it the id and name (e.g. Objects.hash(id, name))
  2. Cart
    1. Add an equals and hashCode methods with IntelliJ shortcut
      1. Click Command + N and select equals and hashCode. Follow the wizard to generate the code.

Map

Details instructions on what each method should do and return is in MyMap class.

Part 2 - ListMap

maybe some more on WHERE to uncomment things? tests or code? A list map stores every entry in a list. Every time the user calls put, create a new Entry and add it to the list. Your task is to make all the test pass.

  1. Uncomment line 178 - 196. Notice how long the test takes to run.

BONUS: Uncomment the remove method and add the code to pass the tests.

Part 3 - MyHashMap

are there any writted descriptions of hashtables as well? If you still have no idea what a HashMap is, watch this video. Notice I add the bucketIndex to help you determine where to store the entry. The bucketIndex uses the hashCode to try to evenly distribute the entries.

  1. put - find which bucket it belongs to, then add it to the list of that bucket
  2. get - find which bucket it belongs to, then loop through the list to find the entry corresponding to the key
  3. Uncomment line 178 - 196. Notice how fast it takes to run.

BONUS: Uncomment the remove method and add the code to pass the tests.

Performance

Notice how long the ListMap takes to store and find 70,000 items. Notice how much faster a HashMap is. In the MyHashMap class, change the BUCKET_SIZE to 100. Run the MyHashMapTest again. Notice how much faster it is. That's the power of designing and using a good data structure. It can speed up your program significantly.