Java 8 Stream - Syntax error on token "(", Expression expected after this token

Bandita Pradhan :

I have not used any Java 8.

Here is the code that I wrote below Java 8 Version.

List<GetOrderResponseType> orders = findOrderResponseType.getOrder();       
List<GetOrderResponseType> openOrders = new ArrayList<GetOrderResponseType>();

if (!CollectionUtils.isEmpty(orders)) { 
            for(GetOrderResponseType order : orders ) {     
                if ( order != null) {
                    if (order.getOrderSummary() != null) {
                        if ( order.getOrderSummary().getState() != null) {

                            if (order.getOrderSummary().getState().toString().toLowerCase().startsWith("open")) {
                                openOrders.add(order);
                            } 
                        }
                    }
                }
            }
        }       
        return openOrders;  

Now, I am trying to change to Java 8 using Streams.

openOrders = orders.stream()
                        .filter(order -> Objects.nonNull(order))
                        .map(order -> order.getOrderSummary())
                        .filter(orderSummary -> Objects.nonNull(orderSummary))
                        .map(orderSummary -> orderSummary.getState())
                        .filter(orderSummaryState -> Objects.nonNull(orderSummaryState))
                        .map(orderSummaryState -> orderSummaryState.toString())
                        .filter(orderSummaryStateStr -> Objects.nonNull(orderSummaryStateStr))
                        .filter(orderSummaryStateStr -> orderSummaryStateStr.toLowerCase().startsWith("open"))
                        .collect(Collectors.toList<GetOrderResponseType>());

on the last statement I am getting Syntax error on token "(", Expression expected after this token.

Thanks, Bandita Pradhan

Andrew Mairose :

The .map() function changes the type of object stored in the stream. For instance, when you do .map(order -> order.getOrderSummary()) you are changing the stream from Stream<GetOrderResponseType> to Stream<OrderSummary>. So on your last step when you try to collect the stream back to a List<GetOrderResponseType>, you can't because you have a Stream<String>, which is the string order summary state, rather than Stream<GetOrderResponseType>.

What you are trying to accomplish may be better done with a single filter, and passing in a method reference that does your filtering, like this:

List<GetOrderResponseType> openOrders = orders.stream()
    .filter(this::isOpenOrder)
    .collect(Collectors.toList());

And then define an isOpenOrder method as such:

private boolean isOpenOrder() {
    if (order == null) {
        return false;
    }
    if (order.getOrderSummary() == null) {
        return false;
    }
    if (order.getOrderSummary().getState() == null) {
        return false;
    }
    return order.getOrderSummary().getState().toString().toLowerCase().startsWith("open");
}