Ok, I think I know how to work with streams now. The code in the old post is a mess and I'm not proud of it. So, thank you for you help for directing me in the right direction. I wrote a supplier class , which provides me with items and used static filters and mapper functions:
final TradeSupplier tradeSupplier = new TradeSupplier();
Stream.generate(tradeSupplier).map(TradeSupplier::getPrice)
.map(TradeSupplier::getTradePartner)
.map(TradeSupplier::getTradeInfo)
.filter(TradeSupplier::validateInfo)
.map(TradeSupplier::getPartnerAssetId)
.filter(TradeSupplier::validatePartnerAssetId).forEach(t -> {
if (trade.sendTrade(t)) {
tradeSupplier.finishedItem();
TradeCache.save(t);
}
});
With this design, I don't need flatMap
, because it's just an one by one mapping. Additional information is filed into the item, which is just in the stream I hope, this code is better than the code below... What do you think? I'm appreciative for any help to improve my understanding of streams :)
I'm looking for help for the "new" stream api of java 8: first I get a list of items, for every item I collect a list of strings and after that, i want to combine the string with their corresponding item:
Is the following code the right way to use this api?
// input is a list of items
analyst.getInRange(wantMinValue, wantMaxValue)
.stream()
.filter(i -> !haveItem.getName().contains(i.getName())
|| (!haveItem.getModel().contains(i.getModel()) && haveItem
.getQuality() > i.getQuality()))
// get extra information and add it to a list (key: item; value: string)
.collect(Collectors.toMap(s -> s, s -> lounge.getItemId(s)))
.entrySet()
.stream()
// delete all null and empty strings
.filter(e -> e.getValue() != null && !e.getValue().isEmpty())
// for every entry in list, create an list and add to result
.forEach(
e -> {
lounge.getListOfValue(e.getValue(), 1)
.stream()
.filter(s -> s != null && !s.isEmpty())
.map(s -> lounge.getStringFromOldString(s))
.filter(s -> s != null && !s.isEmpty())
.collect(
Collectors
.toCollection(HashSet::new))
// add list to resulting list
.forEach(
s -> {
result.add(new TradeLink(s,
haveItem, e.getKey()));
});
});
First thing: .filter(s -> s != null && !s.isEmpty())
Don't include these things unless these are actually things that can happen. Are empty strings or null strings actually going to come up in your application? (If so, that probably reflects a design flaw in the first place. It may be better to let your application crash, because nulls generally shouldn't be in your program in ways like this.)
Second: don't do the mutable thing you're doing here:
.forEach(
e -> {
lounge.getListOfValue(e.getValue(), 1)
.stream()
.filter(s -> s != null && !s.isEmpty())
.map(s -> lounge.getStringFromOldString(s))
.filter(s -> s != null && !s.isEmpty())
.collect(
Collectors
.toCollection(HashSet::new))
// add list to resulting list
.forEach(
s -> {
result.add(new TradeLink(s,
haveItem, e.getKey()));
});
});
Instead, do something like:
.flatMap(e ->
lounge.getListOfValue(e.getValue(), 1)
.stream()
.map(lounge::getStringFromOldString)
.distinct()
.map(s -> new TradeLink(s, haveItem, e.getKey()))
.collect(toList())
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