Removing Values

As our third main functionality, we will implement the ability to remove values from a MyHashMap based on their corresponding key.

However, before we implement the remove method, we need to create one final helper method that will simplify our implementation.

removeEntry Method

Since we are using SimpleEntry<K, V> objects to represent a key/value pair, we also want to be able to remove a SimpleEntry<K, V> object from our hashtable (the reverse of our insert helper method from Part 3).

For this, we will implement a private removeEntry helper method that takes a SimpleEntry<K, V> entry as a parameter and behaves as follows:

  1. Gets the key for the entry using its getKey() method and calculates the appropriate index as in Step 1 of the find method from Part 2 of the lab.

  2. Gets the appropriate LinkedList from the hashtable using the index calculated in Step 1.

  3. Removes the given entry from the LinkedList found in Step 2 by using the LinkedList class’s remove() method.

Here, we assume that the key of the given SimpleEntry<K, V> is already in the hashtable.

remove Method

In Java, removing a key/value pair is accomplished through the method:

public V remove(K key)

If the key was already in the MyHashMap, then the method returns the previous value stored for that key, else it returns null. The pseudocode for this method is:

  1. Use the find method developed above to look up whether key was already in the MyHashMap

  2. If find returns a SimpleEntry<K, V> object because key was already in the HashMap, save the previous value from the SimpleEntry<K, V>. Then call our removeEntry helper method to remove that entry from the hashtable. Next, reduce the size of the MyHashMap since we removed a key. Finally, return the previous value.

  3. If find instead returned null because key was not already in the HashMap, then we have nothing to remove and can simply return null.

Testing the remove Method

Do not forget to write unit tests verifying that the remove method works. It should return the correct values, actually remove key/value pairs (which can be verified using your working get method), and it should appropriately update the size of the MyHashMap.

Committing Your Progress

Don’t forget to frequently save your progress to GitHub using the add/commit/push commands with git.