t'as regardé la jvm?

au moins dans classpath:
http://www.google.fr/codesearch?hl=fr&q=+classpath+String.java+show:UBWIvy4f1Ws:7dr-BbDnUfg:evllEXD0CUw&sa=N&cd=4&ct=rc&cs_p=ftp://ftp.gnu.org/gnu/classpath/classpath-0.92-generics.tar.gz&cs_f=classpath-0.92-generics/java/lang/String.java#first

 /**
   * Computes the hashcode for this String. This is done with int arithmetic,
   * where ** represents exponentiation, by this formula:<br>
   * <code>s[0]*31**(n-1) + s[1]*31**(n-2) + ... + s[n-1]</code>.
   *
   * @return hashcode value of this String
   */
  public int hashCode()
  {
    if (cachedHashCode != 0)
      return cachedHashCode;

    // Compute the hash code using a local variable to be reentrant.
    int hashCode = 0;
    int limit = count + offset;
    for (int i = offset; i < limit; i++)
      hashCode = hashCode * 31 + value[i];
    return cachedHashCode = hashCode;
  }