What criteria do you use when choosing a class to insert an element into a HashMap?

When choosing a class for inserting an element into a HashMap, it is important to ensure that the key is immutable and correctly implements the hashCode() and equals() methods.

Main characteristics:

• Immutability of the key: so that the hash code does not change after insertion, otherwise the element may be lost.
• Correct implementation of hashCode() and equals(): to avoid collisions and ensure proper key comparison.

For example, it is better to use strings, numbers, or custom classes with overridden methods as keys, but not mutable objects like lists or arrays.