private void constrain() {
   BigInteger offset = new BigInteger(Integer.toString(addressSize * (numUsableRows)));
   BigInteger endVal = startVal.add(offset);
   if (endVal.compareTo(scrollBar.getMaximumHP()) > 0) {
     startVal = scrollBar.getMaximumHP().subtract(offset);
     endVal = scrollBar.getMaximumHP();
     scrollBar.setValueHP(startVal);
     model.fireTableDataChanged();
   }
 }
 /** Makes the given address visible somewhere in the window */
 public void makeVisible(Address addr) {
   BigInteger bi = addressToBigInt(addr);
   scrollBar.setValueHP(bi);
 }