Java 相当于 C# Linq 中的 Where 子句
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Java equivalent of Where Clause in C# Linq
提问by jason
I can do this in C# :
我可以在 C# 中做到这一点：
int CheetahNumber = 77;
Animal Cheetah = Model.Animals
.Where(e => e.AnimalNo.Equals(CheetahNumber))
.FirstOrDefault();
For example in Java I have ArrayList<Animal> Animals
例如在Java中我有 ArrayList<Animal> Animals
How can I query such an ArrayList? Thanks.
如何查询这样的 ArrayList？谢谢。
采纳答案by Nick Holt
Java 8 introduces the Stream APIthat allows similar constructs to those in Linq.
Java 8 引入了Stream API，它允许类似于 Linq 中的构造。
Your query for example, could be expressed:
例如，您的查询可以表示为：
int cheetahNumber = 77;
Animal cheetah = animals.stream()
.filter((animal) -> animal.getNumber() == cheetahNumber)
.findFirst()
.orElse(Animal.DEFAULT);
You'll obviously need to workout if a default exists, which seems odd in this case, but I've shown it because that's what the code in your question does.
如果存在默认值，您显然需要进行锻炼，在这种情况下这看起来很奇怪，但我已经展示了它，因为这就是您问题中的代码所做的。
回答by kuhajeyan
Even though there Java does not provide you with LINQ equal constructs but you can achieve some level what LINQ operations with Java 8 stream constructs.
尽管 Java 没有为您提供 LINQ 相等构造，但您可以使用 Java 8 流构造实现某种程度的 LINQ 操作。
such as one
比如一个
List<String> items = new ArrayList<String>();
items.add("one");
items.add("two");
items.add("three");
Stream<String> stream = items.stream();
stream.filter( item -> item.startsWith("o") );
Take a look at java8 stream
看看java8流
回答by Denis Lukenich
You can try it by using streams:
您可以通过使用流来尝试：
public String getFirstDog(List<Animal> animals) {
Animal defaultDog = new Dog();
Animal animal = animalNames.stream(). //get a stream of all animals
filter((s) -> s.name.equals("Dog")).findFirst(). //Filter for dogs and find the first one
orElseGet(() -> defaultDog ); //If no dog available return an default animal.
//You can omit this line.
return animal;
}
