@Override
public void saveState(String prefix, Properties properties) {
    if (hiddenColumnIndexes.size() > 0) {
        StringBuilder strBuilder = new StringBuilder();
        for (Integer index : hiddenColumnIndexes) {
            strBuilder.append(index);
            strBuilder.append(',');
        }
        properties.setProperty(prefix + PERSISTENCE_KEY_HIDDEN_COLUMN_INDEXES, strBuilder.toString());
    }
    
    super.saveState(prefix, properties);
}

@Override
public void loadState(String prefix, Properties properties) {
    String property = properties.getProperty(prefix + PERSISTENCE_KEY_HIDDEN_COLUMN_INDEXES);
    if (property != null) {
        hiddenColumnIndexes.clear();
        
        StringTokenizer tok = new StringTokenizer(property, ","); //$NON-NLS-1$
        while (tok.hasMoreTokens()) {
            String index = tok.nextToken();
            hiddenColumnIndexes.add(Integer.valueOf(index));
        }
    }
    
    super.loadState(prefix, properties);
}