What causes hash code collisions among different objects and how to handle them?

Hash code collisions occur when different objects return the same hash function value. This is related to the limited size of the hash code (for example, a 32-bit integer) and the large number of possible objects.

Reasons for collisions:

• Limited range of hash code values.
• Poor implementation of the hashCode() method, which does not consider all significant fields of the object.

How to handle them:

• Properly implement hashCode() and equals(): consider all fields affecting the object's uniqueness.
• Use good hash functions: that distribute values evenly.
• In hash-based collections (e.g., HashMap), collisions are handled automatically: through chaining or trees.
• During testing: verify that objects with different values have different hash codes, as much as possible.

Example of a correct hashCode() implementation in Java:

@Override
public int hashCode() {
    return Objects.hash(field1, field2, field3);
}