Can Java's hashCode produce same value for different strings?

Question

Is it possible to have same hashcode for different strings using java\'s hashcode function?or if it is possible then what is the % of its possibility?

Answer 1

Yes, it is entirely possible. The probability of a string (or some other object type -- just assuming you'll be using strings in this example) having the same hashcode as some other string in a collection, depends on the size of that collection (assuming that all strings in that collection are unique). The probabilities are distributed as follows:

• With a set of size ~9,000, you'll have a 1% chance of two strings colliding with a hash in the set
• With a set of size ~30,000, you'll have a 10% chance of two strings colliding with a hash in the set
• With a set of size ~77,000, you'll have a 50% chance of two strings colliding with a hash in the set

The assumptions made, are:

• The hashCode function has no bias
• Each string in the aforementioned set is unique

This site explains it clearly: http://eclipsesource.com/blogs/2012/09/04/the-3-things-you-should-know-about-hashcode/ (Look at "the second thing you should know")