方法参考与Lambda表达式 [英] method reference vs lambda expression

问题描述

我想在下面的示例中用方法引用替换lambda表达式:

I want to replace lambda expression by method reference in the below example :

 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);
        }
   }

我想写这样的东西:

words.stream().filter(s::endsWith(".")).forEach(System.out::println);

是否有可能将任何lambda表达式转换为方法引用.

is it possible to transform any lambda expression to method reference.

推荐答案

没有办法将任何lambda表达式转换为方法引用"，但是如果可以满足经常性的需求，则可以为特定的目标类型实现一个工厂:

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:

public static <A,B> Predicate<A> bind2nd(BiPredicate<A,B> p, B b) {
    return a -> p.test(a, b);
}

有了这个，你可以写

words.stream().filter(bind2nd(String::endsWith, ".")).forEach(System.out::println);

但是实际上，没有优势.从技术上讲，lambda表达式可以完全满足您的要求，其中存在最小必要的参数转换代码，表示为lambda表达式的主体，被编译为合成方法和对该合成代码的方法引用.语法
s -> s.endsWith(".")也已经是表达该意图的最小语法.我怀疑您会找到一个较小的结构，该结构仍与其余Java编程语言兼容.

but actually, there’s no advantage. 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. The syntax
s -> s.endsWith(".") also is already the smallest syntax possible to express that intent. I doubt that you can find a smaller construct that would still be compatible with the rest of the Java programming language.

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