ui/src/main/java/ucar/util/prefs/ui/Field.java
protected boolean acceptIfDifferent(Object newValue) {
    // System.out.println("isDifferent "+newValue+" "+value);
    if ((newValue == null) && (validValue == null)) return false;
    if ((validValue != null) && validValue.equals( newValue)) return false;
    previousValue = getValue();
    validValue = newValue;
    return true;
  }
protected boolean acceptIfDifferent(Object newValue) {
    // System.out.println("isDifferent "+newValue+" "+value);
    if ((newValue == null) && (validValue == null)) return false;
    if ((validValue != null) && validValue.equals( newValue)) return false;
    previousValue = getValue();
    validValue = newValue;
    return true;
  }
See if this value is different from current accepted value (using equals());
If so, set old value to accepted value, then accepted value to this value.
@return true if its different.