如何使用自己的比较器按类字段排序?

问题描述

我有一个示例课程，例如 Country :

I have a sample class, say Country:

class Country {
    public String name;
    public int population;
    public Flag flag;  
    ...                                                                        
}

我在其他地方定义了这个 Flag 类

I have this Flag class defined somewhere else

class Flag {
    String id;
    int pixel;
    ...
}

现在，我创建一个单独的比较器DefaultFlagRankingComparator()，可以按ID对Flag进行排序.如何使用此DefaultFlagRankingComparator()按标记ID对国家/地区列表进行排序?

Now I create a separate comparator DefaultFlagRankingComparator() that can sort Flag by id. How can I sort a list of Country by Flag id, using this DefaultFlagRankingComparator()?

推荐答案

您可以使用每个国家/地区的标志字段调用 Comparator 的compare方法.

You can invoke the compare method of the Comparator with the flag field of each country.

DefaultFlagRankingComparator flagComparator =
        new DefaultFlagRankingComparator();
Collections.sort(countries, (a, b) ->
        flagComparator.compare(a.getFlag(), b.getFlag()));

您还可以使用 Comparator.comparing 使用键提取功能和 Comparator 创建 Comparator 比较这些密钥的代码(如 Louis Wasserman 所建议).

You could also use Comparator.comparing to create a Comparator using a key extracting function and a Comparator that compares those keys (as suggested by Louis Wasserman).

DefaultFlagRankingComparator flagComparator =
        new DefaultFlagRankingComparator();
Collections.sort(countries,
        Comparator.comparing(Country::getFlag, flagComparator));

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