Question

我有一个带有以下内容的java 8流循环：

    void matchSellOrder(Market market, Order sellOrder) {
        System.out.println("selling " + market.pair() + " : " + sellOrder);

        market.buyOrders()
                .stream()
                .filter(buyOrder -> buyOrder.price >= sellOrder.price)
                .sorted(BY_ASCENDING_PRICE)
                .forEach((buyOrder) -> {
                    double tradeVolume = Math.min(buyOrder.quantity, sellOrder.quantity);
                    double price = buyOrder.price;

                    buyOrder.quantity -= tradeVolume;
                    sellOrder.quantity -= tradeVolume;

                    Trade trade = new Trade.Builder(market, price, tradeVolume, Trade.Type.SELL).build();
                    CommonUtil.convertToJSON(trade);

                    if (sellOrder.quantity == 0) {
                        System.out.println("order fulfilled");
                        // break loop there
                    }
                });
    }

如果满足某些条件，我怎么能摆脱循环？什么是关闭流的正确方法？

更新

我错误地使用了流tecnique，假设它是一个循环，它不是为此而设计的。以下是我使用以下答案提供的代码：

        List<Order> applicableSortedBuyOrders = market.buyOrders()
                .stream()
                .filter(buyOrder -> buyOrder.price >= sellOrder.price)
                .sorted(BY_ASCENDING_PRICE)
                .collect(toList());

        for(Order buyOrder : applicableSortedBuyOrders){
            double tradeVolume = Math.min(buyOrder.quantity, sellOrder.quantity);
            double price = buyOrder.price;

            buyOrder.quantity -= tradeVolume;
            sellOrder.quantity -= tradeVolume;

            Trade trade = new Trade.Builder(market, price, tradeVolume, Trade.Type.SELL).build();
            CommonUtil.printAsJSON(trade);

            if (sellOrder.quantity == 0) {
                System.out.println("order fulfilled");
                break;
            }
        }

Answer 1

Stream.forEach不是循环，它不是设计用break之类的东西终止的。如果流是并行流，则lambda body可以同时在不同的线程上执行（不容易破坏，并且很容易产生不正确的结果）。

最好使用带有while循环的迭代器：

Iterator<BuyOrderType> iter = market.buyOrders() // replace BuyOrderType with correct type here
            .stream()
            .filter(buyOrder -> buyOrder.price >= sellOrder.price)
            .sorted(BY_ASCENDING_PRICE).iterator();
while (iter.hasNext()) {
    BuyOrderType buyOrder = iter.next()  // replace BuyOrderType with correct type here
    double tradeVolume = Math.min(buyOrder.quantity, sellOrder.quantity);
    double price = buyOrder.price;

    buyOrder.quantity -= tradeVolume;
    sellOrder.quantity -= tradeVolume;

    Trade trade = new Trade.Builder(market, price, tradeVolume, Trade.Type.SELL).build();
    CommonUtil.convertToJSON(trade);

    if (sellOrder.quantity == 0) {
        System.out.println("order fulfilled");
        break;
    }
}

Answer 2

嗯，在流api中没有办法做到这一点，（据我所知）。

但如果您确实需要，则可以使用例外。

编辑：对于给出这个答案-1的人而言，我不会将此作为一个应该遵循的方法做广告，它只是您需要的选项的一个选项它确实回答了这个问题。

public class BreakException extends RuntimeException {...}

try {
    market.buyOrders()
            .stream()
            .filter(buyOrder -> buyOrder.price >= sellOrder.price)
            .sorted(BY_ASCENDING_PRICE)
            .forEach((buyOrder) -> {
                double tradeVolume = Math.min(buyOrder.quantity, sellOrder.quantity);
                double price = buyOrder.price;

                buyOrder.quantity -= tradeVolume;
                sellOrder.quantity -= tradeVolume;

                Trade trade = new Trade.Builder(market, price, tradeVolume, Trade.Type.SELL).build();
                CommonUtil.convertToJSON(trade);

                if (sellOrder.quantity == 0) {
                    System.out.println("order fulfilled");
                    throw new BreakException()
                }
            });
} catch (BreakException e) {
    //Stoped
}

终止或破坏java 8流循环

2 个答案: