Java多级比较器 [英] Java Multi-Level Comparator
问题描述
我正在解决一个问题，我必须从输入文件中获取这些歌曲艺术家对"，并按字母顺序进行排序.排序准则如下:
I am working on a problem where I must take these "Song-artist pairs" from an input file and sort alphabetically. The guidelines to the sorting goes like so:
- 应首先按作者姓名对歌曲艺术家对进行排序.
- 按艺术家排序后，如果同一位艺术家有多首歌曲，则也应按字母顺序对其进行排序.
- 如果艺术家的名字以"The"开头，则出于排序目的将其忽略.
我的问题是，当我对这些歌曲进行排序时，我能够对它们进行正确排序，但是在他们具有相同艺术家的条件下，我无法对歌曲进行排序.
My problem is that when I am sorting these, I am able to get the artists sorted properly, but then I cannot sort the songs under the conditions that they have the same artist.
这是输入文件的外观:
Hello - Adele
Yesterday - The Beatles
Love Me Like You Do - Ellie Goulding
Hey Jude - The Beatles
Istanbul - They Might Be Giants
我已经正确阅读了输入文件，但是到目前为止，我的比较器仅按字母顺序对艺术家进行排序.这是我的比较器的外观:
I have properly read through the input file, but so far my comparator only sorts the artists alphabetically. This is what my comparator looks like:
public static class SongComparator implements Comparator<Song>{
public int compare(Song a, Song b){
return a.effectiveAuthor().compareTo(b.effectiveAuthor());
}
}
(我创建了一个类来轻松跟踪歌曲及其艺术家.有效的Author()方法返回作者的字符串，名称前没有"The")
(I have created a class to easily keep track of the songs and their artists. The effectiveAuthor() method returns the string of the author without the "The " in front of the name)
当使用Song对象和比较器的数组调用Arrays.sort()时，这是我得到的输出:
When calling Arrays.sort() with the array of Song objects and comparator, this is the output I get:
Hello - Adele
Yesterday - The Beatles
Hey Jude - The Beatles
Love Me Like You Do - Ellie Goulding
Istanbul - They Might Be Giants
这是经过正确排序的输出的样子:
This is what the output with the proper sorting would look like:
Hello - Adele
Hey Jude - The Beatles
Yesterday - The Beatles
Love Me Like You Do - Ellie Goulding
Istanbul - They Might Be Giants
我最初的想法是遍历整个数组，找到同一位艺术家的歌曲，然后找到一种对它们进行排序并将其重新插入该数组的方法，这有点复杂.有人告诉我，可以通过使用更全面的比较器来对艺术家和歌曲名称进行排序，并且只需要对所有Song对象调用一次Arrays.sort.
My original idea was to loop through the array and find the songs with the same artist, and find a way to sort them and re-insert those back into that array, which is a bit complex. I was told that I could use a more comprehensive comparator by having them sort both the artist and song names, and that I would only need to call Arrays.sort once for all of the Song objects.
有人可以告诉我如何制作一个适用于这种情况的更全面的比较器吗?我目前仅知道我可以使用比较器的两种方式，即比较数值(即，如果a> b返回-1，如果a == b，则返回0，如果a< b，则返回1)，以及字符串值(又名a.compareTo(b))，但我不知道如何制作更精细的比较器，以帮助我先按歌手然后按歌曲名称排序.
Can somebody show me how to make a more comprehensive comparator that would pertain to this situation? I currently only know two ways that I can use a comparator, which is to compare numerical values(aka if a > b return -1, if a == b, return 0, and if a < b, return 1), and String values(aka a.compareTo(b)), but I do not know how I would be able to make a more elaborate comparator to help me out with being able to sort by artist first and then the song name.
谢谢
PS:这是我提到的Java程序的pastebin，如果您想进一步了解我正在尝试解决的问题. 这是我正在解析的文本文件的样子，其中第一行是测试编号案例，然后是带有歌曲艺术家对数量的数字.
PS: This is a pastebin to the java program I mentioned, if you would like more insight on the problem I am trying to solve. This is what the text file would look like that I am parsing through, where the first line is the number of test cases, followed by a number with the amount of song-artist pairs.
推荐答案
比方说，您说成功创建的类称为SongArtistPair，它具有一个名为effectiveAuthor()的方法，该方法返回作者的姓名而没有getSongName().您可以使用Java 8 Comparator API提供的这种模式.
Let's say the class you said you managed to create is called SongArtistPair and it has a method called effectiveAuthor()which returns the author's name without the The, and a method getSongName() which returns the name of the song. You can use this pattern offered by the Java 8 Comparator API.
Comparator<SongArtistPair> comp = Comparator.comparing(SongArtistPair::effectiveAuthor).thenComparing(SongArtistPair::getSongName);
之后，只需正常使用comp
检查Comparator API文档是否有更酷的内容此处
Check Comparator API docs for more cool stuff HERE
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