根据其字段之一对对象列表进行排序 [英] Sorting a List of Objects Based on 1 of its Fields

问题描述

您好stackoverflow社区！ 我是这些论坛的新手，也是Java和android编程的新手-碰巧是我的问题的对象-因此，如果有任何错误，请提前抱歉！

Hello stackoverflow community! I am new to these forums and also fairly new to java and android programming--which happen to be the objects of my question--so sorry in advance for any blunders!

我的问题是排序.我正在寻找一种根据所选字段对对象进行排序的方法(而不是根据第一个字段进行排序，然后根据下一个字段进行排序，等等，以比较器链接为例).我相信我已经找到解决问题的方法:

My issue is sorting. I am looking for a method to sort objects based on a field that I choose (not sorting based on the first field, then the next, etc. exemplified by comparator chaining). I believe I've found the solution to my problem:

https://stackoverflow.com/a/5113108/1549672

但是我很难让它正常工作.我怀疑由于缺少Java经验而可能缺少某些东西，因此欢迎您提供任何帮助！

but I am having trouble actually getting this to work. I have a suspicion that I'm probably missing something due to my lack of java experience, so any help is welcome!

这是我正在尝试的:

作为我的班级-

public class ItemLocation {
String title;
int id;
}

作为我的职责-

public void sort(final String field, List<ItemLocation> itemLocationList) {
    Collections.sort(itemLocationList, new Comparator<ItemLocation>() {
        @Override
        public int compare(ItemLocation o1, ItemLocation o2) {
            if(field.equals("title")) {
                return o1.title.compareTo(o2.title);
            } else if(field.equals("id")) {
                return Integer.valueOf(o1.id).compareTo(o2.id);
            }
            return 0;
        }
    });
}

使用这些方法，有人可以举一个使用此方法的示例吗?我试图填充ArrayList并对其进行排序，但无济于事.

using these, could someone possibly give an example of using this method? I attempted to fill an ArrayList and sort it, but to no avail.

感谢您的帮助！

推荐答案

您不应从

You should not return 0 from the Comparator.compare method if they are not equal. It's "okey" by the contract, but not exactly encouraged, from the API documentation:

通常是这种情况，但并非严格要求(compare(x， y)== 0)==(x.equals(y)).一般来说，任何比较器 违反此条件应清楚地表明这一事实.这 推荐的语言是注意:此比较器强加了以下命令: 与等式不一致."

It is generally the case, but not strictly required that (compare(x, y)==0) == (x.equals(y)). Generally speaking, any comparator that violates this condition should clearly indicate this fact. The recommended language is "Note: this comparator imposes orderings that are inconsistent with equals."

---

我认为您应该返回特定的 Comparator 而不是每个字段:

---

In my opinion you should return a specific Comparator for each field instead:

Comparator<ItemLocation> titleComparator = new Comparator<ItemLocation>() {
    @Override
    public int compare(ItemLocation o1, ItemLocation o2) {
        return o1.title.compareTo(o2.title);
    }
}

Comparator<ItemLocation> idComparator = new Comparator<ItemLocation>() {
    @Override
    public int compare(ItemLocation o1, ItemLocation o2) {
        return Integer.valueOf(o1.id).compareTo(o2.id);
    }
}

public void sort(final String field, List<ItemLocation> itemLocationList) {

    final Comparator<ItemLocation> comparator;

    if(field.equals("title")) {
        comparator = titleComparator;
    } else if (field.equals("id")) {
        comparator = idComparator;
    } else {
        throw new IllegalArgumentException("Comparator not found for " + field);
    }

    Collections.sort(itemLocationList, comparator);
}

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