Java 8 Lambda - 按另一个集合过滤集合
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Java 8 Lambda - Filter collection by another collection
提问by Shervin Asgari
I have a Set<String> usernamesand List<Player> players
我有一个Set<String> usernames和List<Player> players
I would like to filter out those players that are not in the Set.
我想过滤掉不在系列中的那些玩家。
I know how to do this in Vanilla pre Java 8
我知道如何在 Java 8 之前的 Vanilla 中执行此操作
List<Player> distinctPlayers = new ArrayList<Player>();
for(Player p : players) {
if(!usernames.contains(p.getUsername()) distinctPlayers.add(p);
}
I am trying to write this simple code with a Lambda expression, but I am struggling to get usernames.contains()to work in a filter
我正在尝试使用 Lambda 表达式编写这个简单的代码，但我正在努力usernames.contains()在过滤器中工作
players.stream().filter(!usernames.contains(p -> p.getUsername()))
.collect(Collectors.toList());
This doesn't compile. "Cannot resove method getUsername()"
这不编译。“无法解析方法 getUsername()”
回答by Jon Skeet
You've got the lambda expression in the wrong place - the whole of the argument to filtershould be the lambda expression. In other words, "Given a player p, should I filter it or not?"
你在错误的地方得到了 lambda 表达式 - 整个参数filter应该是 lambda 表达式。换句话说，“给定一个玩家p，我应该过滤它还是不过滤它？”
players.stream().filter(p -> !usernames.contains(p.getUsername()))
