Java方法参考在这里不应该 [英] Java Method reference not expected here

问题描述

您如何精确地链接Java 8实例的方法引用?示例:

How exactly do you chain method references for instances with Java 8? Example:

Collections.sort(civs,Comparator.comparing(Civilization::getStrategy.getStrategLevel));

Civilization实例的

getStrategy返回具有实例方法getStrategyLevel的Strategy对象实例.

getStrategy of a Civilization instance returns a Strategy object instance which has the instance method getStrategyLevel.

为什么Comparator.comparing方法不返回带有由lambda表达式实现的功能接口的比较器?

Why doesn't the Comparator.comparing method return a comparator with it's functional interface implemented by the lambda expression?

推荐答案

在这种情况下，您应该使用lambda，不能直接应用方法引用:

In that case, you should use a lambda, you can't apply a method reference directly:

Collections.sort(civs, Collectors.comparing(c -> c.getStrategy().getStrategLevel()));

但是，这里有一种使用方法引用的方法.假设您有类似的课程

Though, there is a way to use a method reference here. Assuming that you have a class like

class CivilizationUtils {
    public static Integer getKeyExtractor(Civilization c) {
        return c.getStrategy().getStrategLevel();
    }
}

问题可以像

Collections.sort(civs, Collectors.comparing(CivilizationUtils::getKeyExtractor));

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