How to sort the earliest time stamp in the list in java?

Question

package collectionCollections;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.Iterator;
import java.util.List;
import java.util.ListIterator;
import java.util.concurrent.SynchronousQueue;

public class TestCollections {

 public static void main(String[] args) {

  String a = "9:50 PM,12:25 PM,3:55 PM,10:15 PM,1:15 PM";
  ArrayList al2 = new ArrayList();
  ArrayList al3 = new ArrayList();
  String arg[] = a.split(",");
  // System.out.println(arg);
  // Collections.sort(list);
  List < String > al = new ArrayList < String > ();
  al = Arrays.asList(arg);
  for (String s: al) {
   System.out.println(s);
   al2.add(s.substring(0, 5).replace(':', '.'));
  }
  System.out.println(al2);
  Iterator li = al2.iterator();
  while (li.hasNext()) {
   String s = (String) li.next();
   float no = Float.parseFloat(s);
   al3.add(no);
  }
  Collections.sort(al3);
  int add = 0;
  float ff = 0;
  ListIterator lit = al3.listIterator();
  while (lit.hasNext()) {

   float f = (Float) lit.next();
   int intno = (int) f;
   if (intno == 12) {
    add = intno;
    ff = f - add;
    System.out.println(ff);
    lit.remove();
   }
  }
  al3.add(0, add + ff);
  System.out.println(al3);
 }
}

(`I am trying to Sort the below Array list:

my Timestamps = [12:40 PM, 4:00 PM, 7:20 PM, 10:40 PM, 12:00 PM, 3:25 PM, 6:50 PM, 10:15 PM, 6:35 PM, 9:50 PM, 12:20 PM, 3:45 PM, 7:15 PM, 10:40 PM, 11:45 AM, 3:10 PM, 6:35 PM, 10:25 PM, 12:50 PM, 4:10 PM, 7:30 PM, 10:40 PM]

Expected result to display the earliest 11:45 AM in the zeroth index.

I have tried converting above list into integer and when there is unique time (AM/PM)in particular hour(12:35 PM) i was able to sort it but when there are multiple time stamp in particular hour(12:35 PM, 12:05 PM) i am unable to sort.

score 0 · Answer 1 · answered Oct 20 '19 at 13:22

One problem is that a time like 4 PM will show up as 4.0 in your list, thus preceding a time like 11:45 AM (which shows up as 11.45). I suggest taking a look at class like java.util.Date and friends and find a function that converts these times to another format like seconds since midnight or 24 hours notation and then sort on this format.

g.momo · Accepted Answer · 2019-10-20T14:51:13.370

One of the most simple solution for you is the code below with few changes from yours :

convert 12:mm AM/PM by 00:mm AM/PM before sorting
transform hh:mm AM into hh.mm and hh:mm into (hh+12).mm
sort the list

convert hh.mm into hh:mm AM/PM

package collectionCollections;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.Iterator;
import java.util.List;
import java.util.ListIterator;
import java.util.concurrent.SynchronousQueue;

public class TestCollections {

public static void main(String[] args) {

    //String a = "9:50 PM,12:25 PM,3:55 PM,10:15 PM,1:15 PM";
    String a = "9:50 PM,12:25 PM,3:55 PM,10:15 PM,1:15 PM,1:00 AM, 12:25 AM, 10:13 AM";
    List<String> al2 = new ArrayList<>();
    List<Float> al3 = new ArrayList<>();
    List<String> al4 = new ArrayList<>(); // list of final results to display
    String arg[] = a.split(",");
    // System.out.println(arg);
    // Collections.sort(list);
    List<String> al = new ArrayList<String>();
    al = Arrays.asList(arg);
    for (String s : al) {
        System.out.println(s);
        s  = s.trim(); // remove leading and trailing spaces, otherwise the conversion to float will fail
        s = s.replace("12:", "00:"); // do not forget 12:00 is like 00:00 and 12:00 AM/PM is least than 1:00 AM/PM
        String[] t = s.split(" ");
        String ampm = t[1]; // extract AM/PM
        System.out.println("ampm "+ ampm );
        if( ampm.toUpperCase().equals("PM")) {
            String h = t[0].split(":")[0]; // extract hours
            int hh = 12 + Integer.parseInt(h); // add 12 for PM
            t[0] = t[0].replace(h+":", hh+":");
        }

        al2.add(t[0].replace(":", "."));
    }
    System.out.println(al2);
    Iterator li = al2.iterator();
    while (li.hasNext()) {
        String s = (String) li.next();
        float no = Float.parseFloat(s);
        System.out.println(" s -> no : "+ s +" -> "+ no);
        al3.add(no);
    }

    Collections.sort(al3);
    ListIterator lit = al3.listIterator();
    while (lit.hasNext()) {

        float f = (Float) lit.next();
        int intno = (int) f;
        if(intno < 12 ) {
            int hour12 = intno == 0 ? 12 : intno; // replace 00:xx am by 12:xx am
            al4.add(hour12 +":"+ ((int)((f-intno)*100)) +" AM");
        }
        else {
            al4.add((intno-12)+":"+ ((int)((f-intno)*100)) +" PM");
        }
    }
    System.out.println(al4);
}
}

With the list

String a = "9:50 PM,12:25 PM,3:55 PM,10:15 PM,1:15 PM,1:00 AM, 12:25 AM, 10:13 AM";

the result is :

[12:25 AM, 1:0 AM, 10:13 AM, 0:25 PM, 1:14 PM, 3:55 PM, 9:50 PM, 10:14 PM]

A more efficient code is coming in a later edit.

Arvind Kumar Avinash · Answer 3 · 2021-05-16T21:23:48.580

java.time

I recommend you do it using the modern date-time API^*.

import java.time.LocalTime;
import java.time.format.DateTimeFormatter;
import java.time.format.DateTimeFormatterBuilder;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;
import java.util.Locale;

public class Main {
    public static void main(String args[]) {
        String[] timeStrArr = { "12:40 PM", "4:00 PM", "7:20 PM", "10:40 PM", "12:00 PM", "3:25 PM", "6:50 PM",
                "10:15 PM", "6:35 PM", "9:50 PM", "12:20 PM", "3:45 PM", "7:15 PM", "10:40 PM", "11:45 AM", "3:10 PM",
                "6:35 PM", "10:25 PM", "12:50 PM", "4:10 PM", "7:30 PM", "10:40 PM" };
        
        List<String> timeList = Arrays.asList(timeStrArr);
        
        DateTimeFormatter timeFormat = new DateTimeFormatterBuilder()
                                        .parseCaseInsensitive()
                                        .appendPattern("h:m a")
                                        .toFormatter(Locale.ENGLISH);
        Collections.sort(timeList,
                (s1, s2) -> LocalTime.parse(s1, timeFormat).compareTo(LocalTime.parse(s2, timeFormat)));
        
        System.out.println(timeList);
        
        System.out.println("Earliest time in the list: " + timeList.get(0));
    }
}

Output:

[11:45 AM, 12:00 PM, 12:20 PM, 12:40 PM, 12:50 PM, 03:10 PM, 03:25 PM, 03:45 PM, 04:00 PM, 04:10 PM, 06:35 PM, 06:35 PM, 06:50 PM, 07:15 PM, 07:20 PM, 07:30 PM, 09:50 PM, 10:15 PM, 10:25 PM, 10:40 PM, 10:40 PM, 10:40 PM]
Earliest time in the list: 11:45 AM

Update: posting the code with non-lamda expression for sorting (requested by OP in comments section)

import java.time.LocalTime;
import java.time.format.DateTimeFormatter;
import java.time.format.DateTimeFormatterBuilder;
import java.util.Arrays;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;
import java.util.Locale;

public class Main {
    public static void main(String args[]) {
        String[] timeStrArr = { "12:40 PM", "4:00 PM", "7:20 PM", "10:40 PM", "12:00 PM", "3:25 PM", "6:50 PM",
                "10:15 PM", "6:35 PM", "9:50 PM", "12:20 PM", "3:45 PM", "7:15 PM", "10:40 PM", "11:45 AM", "3:10 PM",
                "6:35 PM", "10:25 PM", "12:50 PM", "4:10 PM", "7:30 PM", "10:40 PM" };

        List<String> timeList = Arrays.asList(timeStrArr);

        DateTimeFormatter timeFormat = new DateTimeFormatterBuilder()
                                        .parseCaseInsensitive()
                                        .appendPattern("h:m a")
                                        .toFormatter(Locale.ENGLISH);

        Collections.sort(timeList, new Comparator<String>() {
            public int compare(String s1, String s2) {
                return LocalTime.parse(s1, timeFormat).compareTo(LocalTime.parse(s2, timeFormat));
            }
        });

        System.out.println(timeList);
        System.out.println("Earliest time in the list: " + timeList.get(0));
    }
}

Learn more about the modern date-time API from Trail: Date Time.

^{* For any reason, if you have to stick to Java 6 or Java 7, you can use ThreeTen-Backport which backports most of the java.time functionality to Java 6 & 7. If you are working for an Android project and your Android API level is still not compliant with Java-8, check Java 8+ APIs available through desugaring and How to use ThreeTenABP in Android Project.}

It will be great if you could change it into non Lambda expression, i am not that well versed with Lambda expression. — chandu2798, Oct 22 '19 at 06:36

score 0 · Answer 4 · answered Oct 20 '19 at 17:22

Try using this code. It is compact. Uses Java8 to define a comparator that will do our job for sorting the time in the way. `

  String arg[] = a.split(",");
  List < String > al = new ArrayList < String > ();
  al = Arrays.asList(arg);


  Collections.sort(al, (x,y)->{ 
  int result ;
  String[] splitx = x.trim().split("\\s+");
String[] splity = y.trim().split("\\s+");
if(splitx[1].equals("AM") && splity[1].equals("PM")) {
      result= -1;
  }else if (splitx[1].equals("PM") && splity[1].equals("AM")) {
      result= 1;
  }else {
      result= x.compareTo(y);
  }

  return result;
  });

  System.out.println(al);

`

For input
String a = "12:40 PM, 4:00 PM, 7:20 AM, 10:40 PM, 12:00 PM, 3:25 AM, 6:50 PM, 10:15 PM, 6:35 PM, 9:50 PM, 12:20 PM, 3:45 PM, 7:15 PM, 10:40 PM, 11:45 AM, 3:10 PM, 6:35 PM, 10:25 PM, 12:50 PM, 4:10 PM, 7:30 PM, 10:40 PM";

the output will be :
[ 11:45 AM, 3:25 AM, 7:20 AM, 10:15 PM, 10:25 PM, 10:40 PM, 10:40 PM, 10:40 PM, 12:00 PM, 12:20 PM, 12:50 PM, 3:10 PM, 3:45 PM, 4:00 PM, 4:10 PM, 6:35 PM, 6:35 PM, 6:50 PM, 7:15 PM, 7:30 PM, 9:50 PM, 12:40 PM] Hope it solves your issue.

How to sort the earliest time stamp in the list in java?

4 Answers4

java.time