What is the purpose and main functions of a hash function in programming?

A hash function in programming is designed to transform input data (such as a string or object) into a fixed-size value — a hash code. The main functions of a hash function are:

• Fast indexing and data retrieval (e.g., in hash tables).
• Data integrity verification (checksums).
• Used in cryptography for creating digital signatures and authenticity verification.

Example in Java:

String s = "example";
int hash = s.hashCode();
System.out.println(hash);

Here, the hashCode() method returns an integer hash code of the string, which can be used for quick comparison or storage in collections.