How do I sort an ArrayList include Date and String?

Question

I want to sort my ArrayList by Date. My ArrayList as:

10 June - name
15 April - name
23 July - name
03 March - name

It has day, month and string name. How do I sort by Date?

Thanks

Answer 1

As pointed out by @The Elite Gentleman, you should use a custom comparator. Here's a complete example:

import java.text.*;
import java.util.*;
public class Test {
    public static void main(String[] args) {
        List<String> list = new ArrayList<String>(
                Arrays.asList("10 June - name", 
                              "15 April - name", 
                              "23 July - name", 
                              "03 March - name"));

        // Print list before sorting.
        System.out.println(list);

        // Sort list according to date.
        Collections.sort(list, new Comparator<String>() {
            DateFormat df = new SimpleDateFormat("dd MMM");
            @Override
            public int compare(String s1, String s2) {
                try {
                    Date d1 = df.parse(s1.split("-")[0].trim());
                    Date d2 = df.parse(s2.split("-")[0].trim());
                    return d1.compareTo(d2);
                } catch (ParseException pe) {
                    System.out.println("erro: " + pe);
                    return 0;
                }
            }
        });

        // Print list after sorting
        System.out.println(list);
    }
}

Output:

[10 June - name, 15 April - name, 23 July - name, 03 March - name]
[03 March - name, 15 April - name, 10 June - name, 23 July - name]

( A better idea may however be encapsulate the date/name pairs into a separate class. This would avoid the need to parse the string each time it needs to be used for these type of purposes.)

Answer 2

You can write your own date Comparator and pass sort it using Collections.sort(List<T>, Comparator<? super T> c); method.

Answer 3

Look at Comparator and Comparable .

Answer 4

In the Collections class there is a static method called sort(...) where you can pass a list and a comparator.

Create a comparator that compares the values from the list and return the appropriate value.

Answer 5

Here you an example:

List<Date> dates=new ArrayList<Date>();
dates.add(new Date(System.currentTimeMillis()));
dates.add(new Date(System.currentTimeMillis()+231892738));
dates.add(new Date(System.currentTimeMillis()-742367634));
for(Date d:dates)
    System.out.println(d);
Collections.sort(dates);
for(Date d:dates)
    System.out.println(d);

Or you can use custom comparator

Collections.sort(dates,customComparator);

Answer 6

Try using the Collections.sort method for your case:

Collections.sort(myList, new Comparator<String>(){

    @Override
    public int compare(String s1, String s2) {
          // perform the comparison here and returns a negative integer,
          // zero, or a positive integer as the first argument is less than,
          // equal to, or greater than the second 
    }
    });

Answer 7

create a function which turns that date string into an int? ie

str2int("name 10 June") => 610
str2int("name 15 Jan")  => 115

int str2int(String s){
    String[] elms = s.split("\\s+");
    // ignore first argument which is name
    int day = Integer.parseInt(elms[1]);
    int month = month2int(elms[2]);
    return day + month;
}

// month2int("Jan") => 100
// month2int("Feb") => 200
// .
// .
// month2int("Dec") => 1200

// you get the idea :-)

use a comparator which compares those Strings like that..