使用Java谓词和Lambda [英] Using Java Predicate and Lambda

问题描述

为什么下面的代码返回Predicate<String>而不返回boolean?

Why does the below code return Predicate<String> and not boolean?

我的理解是，此处的!s.isEmpty()检查与谓词boolean test(T t);背道而驰.此处的返回类型为boolean.

My understanding is that the !s.isEmpty() check here is going against the Predicate boolean test(T t); The return type here is boolean.

所以在我的lambda中，我的nonEmptyStringPredicate是否不应该是boolean类型?显然不是，我只是想了解为什么不是这样.

So in my lambda should my nonEmptyStringPredicate not be of type boolean? Obviously, it's not, I'm just trying to understand why it's not.

Predicate<String> nonEmptyStringPredicate = (String s) -> !s.isEmpty();

推荐答案

在这种情况下，Predicate得到一个String作为参数，并返回一个boolean. 如果我们不将其写为lambda，它将看起来像这样:

A Predicate gets in this case a String as parameter and returns a boolean. In case we don't write it as lambda it would look like this:

Predicate<String> somePredicate = new Predicate<String>() {
    @Override
    public boolean test(String string) {
        return !string.isEmpty();
    }
};

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