Bug 128317 group header and footer checkboxes
UI/org.eclipse.birt.report.designer.ui/src/org/eclipse/birt/report/designer/ui/dialogs/GroupDialog.java
* 
	 */
	private void resetInterval( )
	{
		String currentKeyExpression = keyChooser.getText( );
		if ( previoiusKeyExpression.equals( currentKeyExpression ) )
			return;
		if ( ExpressionUtility.isColumnExpression( currentKeyExpression ) )
			intervalChoices = getSubIntervalChoice( );
		else
			intervalChoices = intervalChoicesAll;
		resetIntervalType( intervalChoices );
		previoiusKeyExpression = currentKeyExpression;
	}
	/**
	 * Get subIntervalChoice, could be String,Date,Numeric or All
	 * 
	 * @return
	 */
	private IChoice[] getSubIntervalChoice( )
	{
		Class columnType = getColumnType( );
		if ( columnType == null )
			return intervalChoicesAll;
		if ( String.class.isAssignableFrom( columnType ) )
		{
			return intervalChoicesString;
		}
		else if ( Date.class.isAssignableFrom( columnType ) )
		{