使用Java 8获取属性的最大值 [英] Getting the max of a property using Java 8

问题描述

我想使用Stream库重写下面的代码（ allPeople 是一个 List< Person> ）。

I want to rewrite the below code using the Stream library (allPeople is a List<Person>).

int maxYear = Integer.MIN_VALUE;
Person oldest = null;
for (Person p : allPeople) {
    if (p.getDateOfDeath() > maxYear) {
        oldest = p;
        maxYear = p.getDateOfDeath();
    }
}

我试图找到列表中最老的人人（假设Person对象上没有Age属性，这只是一个例子）。

I am trying to find the oldest person in a list of people (assuming there is no Age property on the Person object, it's just an example).

如何使用Java 8重写它？

How can I rewrite this using Java 8?

推荐答案

Person oldest = allPeople.stream().max(comparingInt(Person::getDateOfDeath)).orElse(null);

此代码创建一个人流，并在比较死亡日期时选择最大元素。这是通过使用 Comparator.comparingInt（keyExtractor） ，密钥提取器是对人员死亡日期的方法参考。

This code creates a Stream of Person and selects the max element when comparing the date of death. This is done by using Comparator.comparingInt(keyExtractor) with the key extractor being a method-reference to the date of death of the person.

如果列表为空，则返回 null 。

If the list was empty, null is returned.

如上所述注释，您也可以使用 Collections.max 但请注意这会抛出 NoSuchElementException 如果列表为空，那么我们需要采取在此之前照顾：

As noted in the comments, you could also use Collections.max but note that this throws a NoSuchElementException if the list is empty so we need to take care of that before:

Person oldest = allPeople.isEmpty() ? null : Collections.max(allPeople, comparingInt(Person::getDateOfDeath));

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