Java Hashmap Duplicate Keys

When adding a duplicate key the old value (for the same key, as keys must be unique) is simply replaced; If you try to insert the duplicate key, it will replace the element of the corresponding key. Subclass | teacher class java public class teacher {

This logic we will implement in the equals () method of the teacher class. Here we will see how to count duplicate values in hashmap using stream api. If the map previously contained a mapping for the key, the old value is replaced.

A hashmap is a data structure that stores 4 elements key, value, hashvalue and a reference/pointer to the next hash map object storing the same thing arraylist;

Once you do so you can retrieve the values of the respective keys but, the values we use for keys should be unique duplicate values As we know hashmap does not allow duplicate keys. I have two ideas to resolve my issue: Associates the specified value with the specified key in this map (optional operation).