• 0

[JAVA] Sorting a set of dates


Question

Hi,

I have a hashmap with filenames as the keys and the related text as its values.

For example:-

Key - mar_2007

Value - March 2007

Key - jun_2008

Value - June 2008

And more like this including variations like may_apr_2008...

How can I sort this data in reverse chronological order i.e latest first...

Please help me with your suggestions.

Link to comment
https://www.neowin.net/forum/topic/681522-java-sorting-a-set-of-dates/
Share on other sites

14 answers to this question

Recommended Posts

  • 0

I think you're gonna have to convert the texts into proper Date vales in order to sort chronologically.

Things like "June 2008" are easy (use SimpleDateFormat), but you will need to code something yourself to cope with "may_apr_2008" (whatever that means!).

  • 0

I'd create a date structure, out it in an ArrayList and then create a comparator and the do Collection.sort();

do a google search on java comparator and collection.sort

public class MyDate implements Comparator{

private int year;

private int month;

... getters and setters, constructor, eqauls()

}

MyDate myDate= new MyDate(1,2006);

myArray.add(myDate);

... etc

myArray.sort(myArray);

  • 0
  _kane81 said:
I'd create a date structure, out it in an ArrayList and then create a comparator and the do Collection.sort();

Date implements Comparable, so you can sort them without having to create a Comparator (unless you want something other than a strictly chronological sort)

  • 0
  _kane81 said:
true, but he isnt specifying a day, guess you could set it to 1... he wants it reversed ... so maybe extend date and override compare and reverse the compare value?

Yes. SimpleDateFormat allows you to parse dates that have things (eg day) missing, so that's OK.

As for the reversed sort... I like your idea - it's almost a one-liner

public int compareTo(Date d) { return - super.compareTo(Date d)}

Its the parsing of the "more like this including variations like may_apr_2008..." that worries me!

  • 0

changed mind :)

my above suggestion is not really good design at all :( - poor seperation of behaviour. You should take a mix of my advice and James.

so here is some example code - seperate out sort behaviour from the object

public class ReverseDateComparator implements Comparator {

	public int compareTo(Date a, Date b) { 
		return - a.compareTo(b)
	}
}

your main
{
   ArrayList<Date> dateList = new ArrayList()

  .. add dates to the list
   dateList.add(new Date());
   .....

  Collection.sort(dateList, new ReverseDateComparator());
}

  • 0

Thanks JamesCherrill and _kane81 :)

I used your ideas and found another solution(may sound wierd)...

My requirement was to get a map with actual filenames as the key and the clean formatted text as the value which is sorted in the chronological order.

for example:-

key = may_2008

value = May 2008

key = mar_16_23_2008

value = May 16-23 2008

key = aug_sep_2007

value = August-September 2007

This must be sorted so that latest docs will be on top. The factor that worried me is the different combinations that can come in the filename part.

Using your suggestions, I extracted a string out of the filename. If the day was specified,I'll use it. Or else I'll put 1 as the day. For month, I took the first month appearing in the name.

Then I parsed it to create a Date object from this string.

I used a TreeMap to store the dates so that it'll be sorted

TreeMap dateList = new TreeMap(Collections.reverseOrder());

The keys were the Date objects and values were the filenames.

I used a LinkedHashMap to retrieve the filenames from the TreeMap.Using a function I formatted the filenames as text to be displayed.

Now the LinkedHashMap contains keys as the filenames and values as the text to be displayed.

Is this a good solution? Or any other optimized solutions are available?

Please put your suggestions.

  • 0

^

hadnt seen "TreeMap(Collections.reverseOrder());" before...

not sure what you are doing there....

I think your solutions sounds fine... however why do you keep using a map? maps are good/quick for lookups on a key. if you just want an ordered list, an arraylist (vector if thread safety is req) would be a better choice as it is more efficent in sorting/ordered stuff.

edit: ok so your keeping a file name link as key... guess thats ok... either that or create a class that encapsulates a date and file name or maybe an actual link to the file....

ie

public class MyFile implements comparable{

File file;

Date date;

public MyFile(File file) {

setFile(file);

}

public void setFile(File file) {

this.file = file;

do some code to parse file name to date

this.date = .....

}

public int compareTo(MyFile file) {

return this.file.getDate().compareTo(file.getDate());

}

}

Edited by _kane81
  • 0

Thanks _kane81 for the valuable inputs.

The existing scenario resembles something like this - in a jsp page, function call is made to get the filenames and the display text. The function is written in a java file and it will return the data in a map.

Now this sorting problem came up and I had to find a solution that will not disrupt the existing system very much.

I used hashMap because I thought it was the best solution. Anyways I need the filenames and the display text built from this filename. By using a Map I can get both with just a single function call.

TreeMap(Collections.reverseOrder()); --> This is a quick solution to reverse the order in Tree Map. As you know, TreeMap sorts in the natural ordering of keys or ascending order. Collections.reverseOrder() will reverse it easily...so I get reverse sorted filename list. Ofcourse it can be done using Comparable interface but this is a very easy and handy solution :) and its working fine...

And I used LinkedHashMap so that the order is preserved as in TreeMap. Thus I can use filenames as keys and display text as values and can be sure that the order is same as the sorted order in TreeMap...

  • 0

Sorry to ressurect this thread but i have a similar problem and wonder if anyone can give me some advices or suggestions.

I am using this method to create a date.

  Quote
public String getDate() {

Calendar cal = Calendar.getInstance();

SimpleDateFormat sdf = new SimpleDateFormat("dd/MM/yyyy");

return sdf.format(cal.getTime());

}

Then i store the DATE as the key and a USER object as the value in a Hashmap. Now i will like to sort the KEY (which is the date) with the latest date at the top.

How can i do this? please advice..

Thanks~

  • 0

Oh no! I just realised that i can't do that. Because the date MAY NOT be unique hence cannot be used as a key!

Anyone can give me some suggestions please? Actually the USER object does contain the date. So is there a way i can sort the USER OBJECT according to the dates but calling user.getDate() from the USER OBJECT and maybe store in an arraylist of USER object?

  • 0

i want to sort set of csv files named with dates

like my filename is

beno_hawai_enc_01-Aug-2009.csv

beno_hawai_enc_03-Aug-2009.csv

beno_hawai_enc_02-Aug-2009.csv

how to read these files in sorted order based on filename please give me some ide its very urgent my email id is deepu.bhanu@gmail.com

thank you

This topic is now closed to further replies.
  • Recently Browsing   0 members

    • No registered users viewing this page.
  • Posts

    • I don't care about browser benchmarks. It's loads pages nearly instantly and doesn't really feel slow at all to me. Anyway I care more about features and stability and so far I'm satisfied. Plus I wouldn't use Edge if Microsoft paid me.
    • And the big problem we have seen with government organizations is the incredibly slow accountability. In the private space, the need to turn a profit forces the issue. That may not always be healthy, but it is swift. The best working example of a government organization is the USPS, but that is in part because it was created to operate like a business, with its own budget and revenue. That model may not work in every case, for example, I wouldn't want law enforcement under pressure to find revenue, but in some cases it does work.
    • Hell Let Loose, and A Little to the Left, and more join Xbox Free Play Days this weekend by Pulasthi Ariyasinghe Microsoft lets every Game Pass subscriber jump into fresh games every weekend for no extra cost, and it's time for another bunch of games to join the fray. The latest update offers Xbox Game Pass Ultimate, Standard, and Core subscribers access to three games: Dragon Ball Xenoverse 2, Hell Let Loose, and A Little to the Left. As usual, any progress made during the weekend also carries over automatically if you decide to purchase a game afterward. From the trio, Hell Let Loose is for shooter fans, offering 50 versus 50 PVP battles across various realistic World War II fronts. However, the gameplay is a much more hardcore experience compared to other shooters on the market. The title features infantry, tanks, and artillery warfare, with 14 roles available that offer different weapons and teamwork-related equipment. Next, Dragon Ball Xenoverse 2 comes in, touting its ties to the massive anime franchise. The title has players time-traveling to the past as a custom Dragon Ball character to make sure historical moments from the storyline happen just as fans remember. While the world itself is a massive one, fights happen in 3D arenas, taking cues from notable locations in the anime universe. If both those games are a bit too action-heavy, A Little to the Left is a cozy puzzle experience that aims to settle your perfectionist needs. The game has you sorting, stacking, and organizing household items from their awkward locations to more pleasing and organized placements. The controls mostly involve drag-and-drop operations, and some puzzles even have multiple solutions for neatness. Here are the three latest Free Play Days games and their supported platforms: Hell Let Loose - $24.99 (Xbox Series X|S, PC) DRAGON BALL XENOVERSE 2 - $5.99 (Xbox Series X|S, Xbox One, PC) A Little to the Left - $7.49 (Xbox Series X|S, Xbox One, PC) This Free Play Days promotion will end on Sunday, June 8, at 11:59 pm PT. Following this, expect another round of games to enter the program next Thursday.
    • AMD 25.6.1 driver out with RX 9060 XT support and a lot more FSR 4 games by Pulasthi Ariyasinghe A brand-new hardware launch is happening today for AMD, and to make sure its new GPUs are running properly, a new graphics driver has also landed right alongside it. The AMD Software: Adrenalin Edition 25.6.1 driver lands with support for the RX 9060 XT and the AMD Radeon AI PRO R9700, while also finally updating the number of games that support its AMD FidelityFX Super Resolution 4 upscaling technology. The consumer space-targeted RX 9060 XT graphics card comes in 8GB and 16GB flavors starting at $300 and $350 price points, respectively. Check out our launch coverage for this RDNA 4 GPU for more details here. At the same time, the AMD Radeon AI PRO R9700 comes in for handling professional workloads with a whopping 32GB of VRAM. While support for this card has already arrived with the latest driver, AMD is expecting to ship the product sometime in July 2025. The driver has also added official support for Onimusha 2: Samurai's Destiny Remaster as well, the Capcom-developed action game from last month. As for fixes, AMD has said that it has resolved reversed Quality and Performance selections in the Radeon Boost UI, as well as Le Mans Ultimate performance issues on RX 9070 series GPUs. There are quite a few known issues AMD is still working on: Stutter and lower than expected performance may be observed when using alt-tab and streaming to Discord with multiple monitors. Intermittent application crash or driver timeout may be observed while playing Marvel Spiderman 2 with Ray Tracing enabled on Radeon™ RX 9060 XT. Intermittent application crash may be observed when first launching The Last of Us Part 1 on Radeon™ RX 9060 XT graphics products. Stutter may be observed while playing games with some VR headsets at 80Hz or 90Hz refresh rate on some AMD Radeon™ Graphics Products such as the Radeon™ RX 7000 series. Users experiencing this issue are recommended to change the refresh rate as a temporary workaround. Intermittent system or application crash may be observed while playing Cyberpunk 2077 on some AMD Radeon™ Graphics Products such as the Radeon™ RX 7000 series. Intermittent application crash or driver timeout may be observed while playing Monster Hunter Wilds with Radeon™ Anti-Lag and Instant Replay enabled. Artifacts or corruption may appear while playing Battlefield™ V on Radeon™ RX 7000 series graphics products. Stutter may be observed while playing Call of Duty®: Warzone™ Season 03 ‘Verdansk’ map on some AMD Graphics Products. Stutter and lower than expected performance may be observed while playing 4K resolution YouTube videos in Chromium. Users experiencing this issue are recommended to play videos in full screen as a temporary workaround. Texture flickering or corruption may appear while playing The Elder Scrolls IV: Oblivion Remastered with AMD FidelityFX™ Super Resolution enabled on Radeon™ RX 9070 XT. Users experiencing this issue are recommended to disable AMD FidelityFX™ Super Resolution as a temporary workaround. As for FSR 4, these games are now supported by the popular upscaling tech for gaining more frames: Deadzone: Rogue Rem Survival F1 25 Runescape: Dragonwilds Frostpunk 2 Star Wars Outlaws Legacy: Steel & Sorcery Steel Seed Lords of the Fallen Stellar Blade Planetaries Virtua Fighter 5 R.E.V.O QANGA Wild Assault The complete list of games with FSR 4 support, as well as upcoming implementations, can be found on AMD's support page here. The WHQL-certified AMD Software: Adrenalin Edition 25.6.1 driver can now be downloaded from the AMD Software app as well as the changelog page on its official website here.
  • Recent Achievements

    • Week One Done
      jbatch earned a badge
      Week One Done
    • First Post
      Yianis earned a badge
      First Post
    • Rookie
      GTRoberts went up a rank
      Rookie
    • First Post
      James courage Tabla earned a badge
      First Post
    • Reacting Well
      James courage Tabla earned a badge
      Reacting Well
  • Popular Contributors

    1. 1
      +primortal
      406
    2. 2
      +FloatingFatMan
      181
    3. 3
      snowy owl
      176
    4. 4
      ATLien_0
      170
    5. 5
      Xenon
      135
  • Tell a friend

    Love Neowin? Tell a friend!