[英]method reference vs lambda expression
I want to replace lambda expression by method reference in the below example : 我想通过以下示例中的方法引用替换lambda表达式:
public class Example {
public static void main(String[] args) {
List<String> words = Arrays.asList("toto.", "titi.", "other");
//lambda expression in the filter (predicate)
words.stream().filter(s -> s.endsWith(".")).forEach(System.out::println);
}
}
I want to write a something like this : 我想写一下这样的东西:
words.stream().filter(s::endsWith(".")).forEach(System.out::println);
is it possible to transform any lambda expression to method reference. 是否可以将任何lambda表达式转换为方法引用。
There is no way “to transform any lambda expression to method reference”, but you can implement a factory for a particular target type, if this serves recurring needs: 没有办法“将任何lambda表达式转换为方法引用”,但您可以为特定目标类型实现工厂,如果这样可以满足重复需求:
public static <A,B> Predicate<A> bind2nd(BiPredicate<A,B> p, B b) {
return a -> p.test(a, b);
}
with this, you can write 有了这个,你可以写
words.stream().filter(bind2nd(String::endsWith, ".")).forEach(System.out::println);
but actually, there's no advantage. 但实际上,没有优势。 Technically, a lambda expression does exactly what you want, there's the minimum necessary argument transformation code, expressed as the lambda expression's body, compiled into a synthetic method and a method reference to that synthetic code. 从技术上讲,lambda表达式完全符合您的要求,它是最小的必要参数转换代码,表示为lambda表达式的主体,编译为合成方法和对该合成代码的方法引用。 The syntax 语法
s -> s.endsWith(".")
also is already the smallest syntax possible to express that intent. s -> s.endsWith(".")
也是表达该意图的最小语法。 I doubt that you can find a smaller construct that would still be compatible with the rest of the Java programming language. 我怀疑你能找到一个仍然与Java编程语言的其余部分兼容的小构造。
You can use selectWith()
from Eclipse Collections . 您可以使用Eclipse Collections中的 selectWith()
。 selectWith()
takes a Predicate2 which takes 2 parameters instead of a Predicate
. selectWith()
接受一个Predicate2 ,它接受2个参数而不是Predicate
。 The second parameter to selectWith()
gets passed as the second parameter to the Predicate2
every time it's called, once per item in the iterable. 每次调用时, selectWith()
的第二个参数作为第二个参数传递给Predicate2
,每个项目在iterable中传递一次。
MutableList<String> words = Lists.mutable.with("toto.", "titi.", "other");
words.selectWith(String::endsWith, ".").each(System.out::println);
By default Eclipse Collections is eager, if you want to iterate lazily then you can use asLazy()
默认情况下,Eclipse Collections是急切的,如果你想懒惰地迭代,那么你可以使用asLazy()
words.asLazy().selectWith(String::endsWith, ".").each(System.out::println);
If you can't change from List
: 如果您无法从List
更改:
List<String> words = Arrays.asList("toto.", "titi.", "other");
ListAdapter.adapt(words).selectWith(String::endsWith, ".").each(System.out::println);
Eclipse Collections' RichIterable has several other *With methods which work well with method references, including rejectWith()
, partitionWith()
, detechWith()
, anySatisfyWith()
, allSatisfyWith()
, noneSatisfyWith()
, collectWith()
Eclipse Collections的RichIterable还有其他几个* With方法可以很好地处理方法引用,包括rejectWith()
, partitionWith()
, detechWith()
, anySatisfyWith()
, allSatisfyWith()
, noneSatisfyWith()
, collectWith()
Note: I am a contributor to Eclipse Collections. 注意:我是Eclipse Collections的贡献者。
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