java 根据其中一个字段对对象列表进行排序
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/11775980/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
Sorting a List of Objects Based on 1 of its Fields
提问by user1549672
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!
你好 stackoverflow 社区！我是这些论坛的新手，对 java 和 android 编程也很陌生——这恰好是我的问题的对象——所以提前为任何错误道歉！
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:
我的问题是排序。我正在寻找一种方法来根据我选择的字段对对象进行排序（不是根据第一个字段排序，然后是下一个字段，等等，以比较器链接为例）。我相信我已经找到了解决问题的方法：
https://stackoverflow.com/a/5113108/1549672
https://stackoverflow.com/a/5113108/1549672
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!
但我在实际使用它时遇到了麻烦。我怀疑由于我缺乏 Java 经验，我可能遗漏了一些东西，所以欢迎任何帮助！
Here is what I am trying:
这是我正在尝试的：
As my class-
作为我的班级-
public class ItemLocation {
String title;
int id;
}
As my function-
作为我的功能-
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;
}
});
}
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.
使用这些，有人可以举一个使用这种方法的例子吗？我试图填充一个 ArrayList 并对其进行排序，但无济于事。
Thanks for the help!
谢谢您的帮助！
回答by dacwe
You should not return 0from the Comparator.comparemethod if they are not equal. It's "okey" by the contract, but not exactly encouraged, from the API documentation:
如果它们不相等，则不0应从该Comparator.compare方法返回。从 API 文档来看，合同是“好的”，但并不完全鼓励：
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."
通常是这种情况，但并不严格要求 (compare(x, y)==0) == (x.equals(y))。一般而言，任何违反此条件的比较器都应清楚表明这一事实。推荐的语言是“注意：这个比较器强加了与 equals 不一致的排序。”
In my opinion you should return a specific Comparatorfor each field instead:
在我看来，您应该Comparator为每个字段返回一个特定的：
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);
}
回答by Martin
Can you post the calling code that is not working? I can't see anything clearly wrong with the code you've provided.
您可以发布不起作用的调用代码吗？我看不出你提供的代码有什么明显的错误。
Firstly, you might try is putting an extra else case like so:
首先，您可以尝试放置一个额外的 else 案例，如下所示：
else {
throw new IllegalArgumentException("Unrecognised field name");
}
At the moment, if you had a typo in your calling code, the comparator would always return 0, which would leave the list unsorted.
目前，如果您的调用代码中有拼写错误，比较器将始终返回 0，这将使列表未排序。
A more robust way of passing the field would be to declare an enum:
传递该字段的更强大的方法是声明一个枚举：
enum ItemLocationField {
TITLE,
ID
}
Then your conditions would become:
那么你的条件就会变成：
if (field == ItemLocationField.TITLE)
and so on. That would reduce the chances of making a typo (the compiler will tell you if you do).
等等。这将减少打错字的机会（编译器会告诉你如果你这样做了）。
回答by amicngh
I don't see anything wrong except returning 0and comparing parameter with equals. you can improve it by throwing RuntimeExceptionrather than returning 0and use equalsIgnoreCaserather than equalsmethod , better to ignore the case of parameter.
除了returning 0将参数与equals. 您可以通过throwing RuntimeException而不是returning 0使用equalsIgnoreCase而不是equals方法来改进它，最好忽略参数的情况。
public static void sort(final String field, List<ItemLocation> itemLocationList) {
Collections.sort(itemLocationList, new Comparator<ItemLocation>() {
@Override
public int compare(ItemLocation o1, ItemLocation o2) {
if(field.equalsIgnoreCase("title")) {
return o1.title.compareTo(o2.title);
} else if(field.equalsIgnoreCase("id")) {
return Integer.valueOf(o1.id).compareTo(o2.id);
}else
throw new IllegalArgumentException("Invalid Parameter .");
}
});
}
回答by Kumar Vivek Mitra
1.If you want to Sort object on the basis of only one attribute, then go for java.lang.ComparableInterface along with Collections.sort(List<T> list)
1.如果你只想根据一个属性对对象进行排序，那么就选择java.lang.ComparableInterface 和Collections.sort(List<T> list)
2.If you want to Sort the object on the basis of more than one attributes, then go for
java.util.ComparatorInterface along with Collections.sort(List<T> list, Comparator<? super T> c)
2.如果要根据多个属性对对象进行排序，请选择
java.util.ComparatorInterface 以及Collections.sort(List<T> list, Comparator<? super T> c)
