java - 终止或中断 java 8 流循环

Question

这个问题在这里已经有了答案:

Limit a stream by a predicate (19 个回答)

关闭 8年前。

我有一个包含以下内容的 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
                    }
                });
    }

满足某些条件时如何跳出循环？无论如何，关闭流的正确方法是什么？

更新

我误用了流技术，假设它是一个循环，它不是为此而设计的。这是我最终使用下面提供的答案的代码:

        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 不是一个循环，也不是为使用 break 之类的东西终止而设计的。如果流是并行流，则 lambda 主体可以同时在不同的线程上执行(不容易破坏它，而且很容易产生错误的结果)。

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;
    }
}