https://github.com/openjdk/jdk/blob/7f02f07f754c942735ba15d70858cd1661a658c0/src/hotspot/share/classfile/stringTable.cpp#L332-L342

oop StringTable::intern(oop string, TRAPS) {
  if (string == nullptr) return nullptr;
  ResourceMark rm(THREAD);
  int length;
  Handle h_string (THREAD, string);
  jchar* chars = java_lang_String::as_unicode_string(string, length,
                                                     CHECK_NULL);
  oop result = intern(h_string, chars, length, CHECK_NULL);
  return result;
}

The "chars" are used for computing the hashcode. However, we can just call java_lang_String::hash_code(oop), which will compute the hashcode for us without making the extra allocation.

==========================
Fixing this will help improve start-up time, as the following one-liner today causes about 4400 calls to String::intern().

import java.text.*;
class DateFormatTest {
  public static void main(String args[]) {
    SimpleDateFormat t = new SimpleDateFormat();
  }
}