如何按 2 个字段对对象进行排序 Java

Question

我要读取的文件如下所示：

1995     Pokemon    Ikue Ôtani  
1940     Tom and Jerry    William Hanna 
1995     Pokemon    voice actor2
1940     Tom and Jerry    voice actor3
2000     Cartoon      voice actor

它有大约 20k 行。 我已经读取文件并将数据存储在 object 中。

        in = new BufferedReader(new FileReader(cartoonsFile));
            
        ArrayList<String> voiceActors = new ArrayList<>();  
        ArrayList<Cartoon> cartoons = new ArrayList<>();    
        
        //read each line
        String line = in.readLine();
        while (line != null) {
            String[] columns = line.split("\\t");
            String year = columns[0];
            String cartoon = columns[1];
            String voiceActor = columns[2];

            //make new object and store data

            Cartoon c = new Cartoon(Integer.parseInt(columns[0]),
                                    columns[1], columns[2]));
            cartoons.add(c); //add to the array list

Object

public class Cartoon {
  private int year;
  private String title;
  private String voiceActor;

  public Cartoon(int year, String title, String voiceActor) {
    this.year = year;
    this.title = title;
    this.voiceActor = voiceActor;
  }
};

我想在线程中读取文件并按年份排序。 谁能提供有关如何一起实现多线程和合并排序的示例代码？

我想得到的 output

1940     Tom and Jerry         William Hanna 
                               voice actor2
                               voice actor3
                               voice actor4
                               voice actor5

1995     Pokemon               Ikue Ôtani  
                               voice actor2

         A Cartoon             voice actor1
                               voice actor2
                               voice actor3

2000     Cartoon               voice actor

Answer 1

尝试这个。

List<CartoonYear> readAndSortByYear(String inFile) throws IOException {
    return Files.readAllLines(Paths.get(inFile))
        .parallelStream()
        .map(line -> line.split("\\t"))
        .map(columns -> new CartoonYear(Integer.parseInt(columns[0]), columns[1], columns[2]))
        .sorted(Comparator.comparing(CartoonYear::getYear))
        .collect(Collectors.toList());
}

Answer 2

坚持你的数据结构（只是将它从相当奇特的CartoonYear重命名为Cartoon ），并坚持使用 @saka1029 的 Java 流的好方法（而不是手动实现合并排序算法），你可以这样做：

package org.acme;

import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.util.List;
import java.util.Map;
import java.util.stream.Collectors;

public class Cartoon {
  private int year;
  private String title;
  private String voiceActor;

  public Cartoon(int year, String title, String voiceActor) {
    this.year = year;
    this.title = title;
    this.voiceActor = voiceActor;
  }

  public static Map<String, List<Cartoon>> readAndGroupByYearAndTitle(String inFile) throws IOException {
    return Files.readAllLines(Paths.get(inFile))
      .parallelStream()
      .map(line -> line.split("\\t"))
      .map(columns -> new Cartoon(Integer.parseInt(columns[0]), columns[1], columns[2]))
      .collect(Collectors.groupingBy(cartoon -> String.format("%4d %s", cartoon.year, cartoon.title)));
  }

  public static void main(String[] args) throws IOException {
    Map<String, List<Cartoon>> cartoonsGrouped = readAndGroupByYearAndTitle(args[0]);
    cartoonsGrouped.keySet()
      .parallelStream()
      .sorted()
      .forEachOrdered(group -> {
        boolean firstElement = true;
        for (Cartoon cartoonYear : cartoonsGrouped.get(group)) {
          if (firstElement) {
            System.out.printf("%4d  %-25s  %s%n", cartoonYear.year, cartoonYear.title, cartoonYear.voiceActor);
            firstElement = false;
          }
          else
            System.out.printf("%4s  %-25s  %s%n", "", "", cartoonYear.voiceActor);
        }
      });
  }
}

这只是快速而肮脏的，而不是我引以为豪的代码。 您要求每组只打印一次年份和标题也不会使if-else代码更好。 但是假设你有一个这样的输入文件：

1995    Pokemon Ikue Ôtani
1940    Tom and Jerry   William Hanna
11  Sample  foo
1995    Pokemon voice actor2
1940    Tom and Jerry   voice actor3
2000    Cartoon voice actor
11  Sample  bar

你会得到 output 像这样：

  11  Sample                     foo
                                 bar
1940  Tom and Jerry              William Hanna
                                 voice actor3
1995  Pokemon                    Ikue Ôtani
                                 voice actor2
2000  Cartoon                    voice actor