code: private void copyArrays() {
          String[] oldSyms = mSymbols;
          int size = oldSyms.length;
          mSymbols = new String[size];
          System.arraycopy(oldSyms, 0, mSymbols, 0, size);
          Bucket[] oldBuckets = mBuckets;
          size = oldBuckets.length;
          mBuckets = new Bucket[size];
          System.arraycopy(oldBuckets, 0, mBuckets, 0, size);
      }
docs: Method called when copy-on-write is needed; generally when first
  change is made to a derived symbol table.