Is it possible to get String value back from its hash code?

Question

Java doc for method String#hashCode() says:

Returns a hash code for this string. The hash code for a String object is computed as

 s[0]*31^(n-1) + s[1]*31^(n-2) + ... + s[n-1]

using int arithmetic, where s[i] is the ith character of the string, n is the length of the string, and ^ indicates exponentiation. (The hash value of the empty string is zero.)

Questions:

• Is it possible to have same hash code for two string objects having different values? If yes then please share some examples.
• Is it possible to get String value back from its hash code?

I am not using it any where in code. I have just asked this question to know more about Java String class.

Answer 1

Is it possible to have same hash code for two string objects having different values? If yes then please share some examples.

Here is a small sample of randomly generated examples of short strings with identical hash codes:

String 1   String 2   Common hash code
--------   --------   ----------------
VTBHKIGV - FLXCLLII        -1242944431
FPESRBAH - GNFWMYVA         1778061647
UYDHRTXL - HGCNRCBE         1509241566
VXQMFMDE - YMYXDWKK        -1553987354
VGWBSYRX - JZNQSUXK          700334696

Since multiple strings can share the same hash code, restoring the original from the hash is not possible.