提示:要否定collection.stream().anyMatch(…)，可以使用collection.stream().noneMatch(…)

根据别人的回答和个人经验:

Predicate<String> blank = String::isEmpty;
content.stream()
       .filter(blank.negate())

谓词#否定不是你要找的吗?

你可以用long emptyStrings = s.filter(s->!s. isempty ()).count();

谓词有方法和，或和否定。

然而，String::isEmpty不是一个谓词，它只是一个String ->布尔lambda，它仍然可以成为任何东西，例如Function<String，布尔>。首先需要进行类型推断。filter方法隐式地推断类型。但如果你在传递它作为参数之前对它求反，它就不再发生了。正如@axtavt提到的，显式推理可以被用作一种丑陋的方式:

s.filter(((Predicate<String>) String::isEmpty).negate()).count()

在其他答案中还有其他建议，静态而不是方法和lambda最有可能是最好的想法。tl和dr部分到此结束。

但是，如果您想更深入地理解lambda类型推断，我想通过示例更深入地解释它。看看这些，看看会发生什么:

Object obj1                  = String::isEmpty;
Predicate<String> p1         = s -> s.isEmpty();
Function<String, Boolean> f1 = String::isEmpty;
Object obj2                  = p1;
Function<String, Boolean> f2 = (Function<String, Boolean>) obj2;
Function<String, Boolean> f3 = p1::test;
Predicate<Integer> p2        = s -> s.isEmpty();
Predicate<Integer> p3        = String::isEmpty;

obj1 doesn't compile - lambdas need to infer a functional interface (= with one abstract method) p1 and f1 work just fine, each inferring a different type obj2 casts a Predicate to Object - silly but valid f2 fails at runtime - you cannot cast Predicate to Function, it's no longer about inference f3 works - you call the predicate's method test that is defined by its lambda p2 doesn't compile - Integer doesn't have isEmpty method p3 doesn't compile either - there is no String::isEmpty static method with Integer argument

另一种选择是在明确的上下文中使用lambda强制转换为一个类:

public static class Lambdas {
    public static <T> Predicate<T> as(Predicate<T> predicate){
        return predicate;
    }

    public static <T> Consumer<T> as(Consumer<T> consumer){
        return consumer;
    }

    public static <T> Supplier<T> as(Supplier<T> supplier){
        return supplier;
    }

    public static <T, R> Function<T, R> as(Function<T, R> function){
        return function;
    }

}

．.． 然后静态导入实用程序类:

stream.filter(as(String::isEmpty).negate())