具有多个字段的Collections.sort [英] Collections.sort with multiple fields

问题描述

我有一个包含三个字段（所有字符串类型）的报表对象列表 -

I have a list of "Report" objects with three fields (All String type)-

ReportKey
StudentNumber
School

我有一个排序代码像 -

I have a sort code goes like-

Collections.sort(reportList, new Comparator<Report>() {

@Override
public int compare(final Report record1, final Report record2) {
      return (record1.getReportKey() + record1.getStudentNumber() + record1.getSchool())                      
        .compareTo(record2.getReportKey() + record2.getStudentNumber() + record2.getSchool());
      }

});

由于某种原因，我没有排序顺序。一个建议在字段之间放置空格，但为什么？

For some reason, I don't have the sorted order. One advised to put spaces in between fields, but why?

你看到代码有什么错误吗？

Do you see anything wrong with the code?

推荐答案

您看到代码有什么问题吗？

Do you see anything wrong with the code?

是。为什么要在比较之前将三个字段添加到一起？

Yes. Why are you adding the three fields together before you compare them?

我可能会这样做：（假设字段是按照您希望排序的顺序）

I would probably do something like this: (assuming the fields are in the order you wish to sort them in)

@Override public int compare(final Report record1, final Report record2) {
    int c;
    c = record1.getReportKey().compareTo(record2.getReportKey());
    if (c == 0)
       c = record1.getStudentNumber().compareTo(record2.getStudentNumber());
    if (c == 0)
       c = record1.getSchool().compareTo(record2.getSchool());
    return c;
}

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