读取txt文件并将行作为对象放入列表

Question

Lets say that we have a text file like this:

what i am trying to do is produce a list in descending order with using a DatePeople and DateComparator classes (using collection.sort)

what i couldnt really understand is after reading txt file how do i put them in correct way into arraylist as DatePeople object ??

List<DatePeople> list = new ArrayList();
        Scanner filenamereader = new Scanner(System.in);
        System.out.println("Enter file name(input.txt): ");
        String fileName = filenamereader.next();
        System.out.println(fileName);
        filenamereader.close();
        try{
            Scanner s = new Scanner(new File(fileName));

            while (s.hasNext()){
                list.add()); ??
        //list.add(new DatePeople(name,year,month,day)); something like this i guess ?
            }
            s.close();

        }catch(IOException io){

            io.printStackTrace();
        }

DatePeople:

public class DatePeople
{

    DatePeople(){

    }
        private String name;
        private int day;
        private int month;
        private int year;


    }

DateComparator:

public class DateComparator implements Comparator<DatePeople> {
public DateComparator(){

    }

    @Override
    public int compare(DatePeople o1, DatePeople o2) {




        return 0;
    }
}

Answer 1

You will need to create an object for each line before you can add it to the list of objects

 while (s.hasNext()){
//create your DatePeople object here
// then add it to the list
DatePeople obj = new DatePeople(name,year,month,day); 
                list.add(obj); 
        //list.add(new DatePeople(name,year,month,day)); something like this i guess ?
            }
            s.close();

You also need to create a constructor in your DatePeople class that takes the name,year,month,day arguments.

As it stands you have three variable for your year,month and day. Not sure if that is intentional. Or you could just have name and date variables in your class.

Answer 2

If you know that the data is standardized, then you can parse it based on the known rules.

String line = s.nextLine();
String[] bits = line.split(" ", 2);
String name = bits[0];
String[] dateBits = bits[1].split("-", 3);
int year = Integer.parseInt(dateBits[0]);
int month = Integer.parseInt(dateBits[1]);
int day = Integer.parseInt(dateBits[2]);

list.add(new DatePeople(name, year, month, day));

Then you'll need a constructor where you pass values in DatePeople, ie:

DatePeople(String n, int y, int m, int d) {
    this.name = n;
    this.year = y;
    this.month = m;
    this.day = d;
}

Alternatively, you could have a parseDatePerson(String line) {} method in DatePeople that contains my first code segment, and then you simply put

list.add(new DatePeople(s.nextLine()));

This would call a constructor in DatePeople that looks like:

DatePeople(String line) {
    parseDatePerson(line);
}

Answer 3

DateComparator

import java.util.*;
import java.io.File;
class DateComparator implements Comparator<DatePeople> {
    @Override
    public int compare(DatePeople o1, DatePeople o2) {
        if(o1.year>o2.year)
        {
          return -1;
        }
        else if(o1.year<o2.year){
          return 1;
        }
        else
        {
          if(o1.month>o2.month)
          {
            return -1;
          }
          else if(o1.month<o2.month){
            return 1;
          }
          else{
            if(o1.day>o2.day)
            {
              return -1;
            }
            else if(o1.day<o2.day){
              return 1;
            }
            else{
              return 0;
            }
          }
        }
    }
}

DatePeople

class DatePeople
{
         String name;
         int day;
         int month;
         int year;

    DatePeople(String name,int year,int month,int day){
      this.name=name;
      this.day=day;
      this.month=month;
      this.year=year;
    }

    }

Main

class Main {
  public static void main(String[] args) {
    List<DatePeople> list = new ArrayList();
        Scanner filenamereader = new Scanner(System.in);
        System.out.println("Enter file name(input.txt): ");
        String fileName = filenamereader.next();
        System.out.println(fileName);
        filenamereader.close();
        try{
            Scanner s = new Scanner(new File(fileName));
            while (s.hasNext()){
              String s1[]=s.nextLine().split(" ");
              String s2[]=s1[1].split("-");
              list.add(new DatePeople(s1[0],Integer.parseInt(s2[0]),Integer.parseInt(s2[1]),Integer.parseInt(s2[2])));
            }
            Collections.sort(list,new DateComparator());  
            for(DatePeople dp:list)
            {
              System.out.println(dp.year+"-"+dp.month+"-"+dp.day+" "+dp.name);
            }

            s.close();

        }catch(Exception io){

            io.printStackTrace();
        }
  }
}