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

if it is possible then what is the % of its possibility?

That is not a particularly meaningful question.

However, unless there is some systemic bias in the String::hashcode function or the way that you are generating the String objects, the probability that any two different (non-equal) String objects will have the same hash code will be 1 in 2³².

This assumes that the Strings are chosen randomly from the set of all possible String values. If you restrict the set in various ways, the probability will vary from the above number. (For instance, the existence of the "FB" / "Ea" collision means that the probability of a collision in the set of all 2 letter strings is higher than the norm.)

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Another thing to note is that the chance of 2³² different strings chosen at random (from a much larger unbiased set of strings) having no hash collisions is vanishingly small. To understand why, read the Wikipedia page on the Birthday Paradox.

In reality, the only way you are going to get no hash collisions in a set of 2³² different strings is if you select or generate the strings. Even forming the set by selecting randomly generated strings is going to be computationally expensive. To produce such a set efficiently, you would need to exploit the properties of the String::hashCode algorithm, which (fortunately) is specified.