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Sorting an array by date/time

Posted on 2004-07-31
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Last Modified: 2012-05-05
I'm fairly new to Java, so I'll try and explain what I need properly.

I've got a frame, which reads a text containing log entries.  However, the log entries will not be in any kind of order, but when I display them, I'd like them to be in date/time order.

An example entry would be:-

31/07/2004-10:00-Log entry.
15/07/2004-09:00-Another log entry.

So, how can I display those entries (note the log file could contain an infinate number of entries) in a list box in my frame? You may need to supply all of the code for the frame/file reading bit - although I can do it myself, it could cause problems inserting code into the mess I've already created!

Finally, this will be inside another program, so I already have a main function. The screen will be called from other methods in other java files.

Hope I've explained it properly. If not, just let me know.

Thanks,

Adrian Johnson
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Question by:adrianjohnson
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13 Comments
 
LVL 92

Expert Comment

by:objects
ID: 11683246
Use Arrays.sort() method to sort your array, using a custom Comparator that does the date/time comparison (or Collections.sort() if in a collection)
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Accepted Solution

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CEHJ earned 200 total points
ID: 11683467
You need to parse your file into classes that can be made into entries in a List model. Run this - the entries have been hard-coded. You will supply yours from file:

import java.text.SimpleDateFormat;
import java.util.Date;

public class LogEntry implements Comparable {
      private final static String DATE_FORMAT_STRING = "dd/MM/yyyy-HH:mm";
      private final static int DATE_PARSE_OFFSET = 16;
      private String datePart;
      private String entry;
      private Date date;
      private SimpleDateFormat format;

      public LogEntry(String entry) {
            format = new SimpleDateFormat(DATE_FORMAT_STRING);
            parse(entry);
      }

      public void setDatePart(String datePart) {
            this.datePart = datePart;
      }

      public String getDatePart() {
            return datePart;
      }

      public void setEntry(String entry) {
            this.entry = entry;
      }

      public String getEntry() {
            return entry;
      }

      public Date getDate() {
            return date;
      }

      public String toString() {
            return entry;
            // or the following for just the date
            //return datePart;
      }

      private void parse(String entry) {
            this.entry = entry;
            datePart = entry.substring(0, DATE_PARSE_OFFSET);
            try {
                  date      = format.parse(datePart.trim());
            }
            catch(Exception e) {
                  e.printStackTrace();
                  System.out.println("Date part is: " + datePart);
            }
      }

      public int compareTo(Object other) {
            LogEntry otherEntry = (LogEntry)other;
            return date.compareTo(otherEntry.getDate());
      }

      // TESTING PURPOSES ONLY!
      public static void main(String[] args) {

            String entry1 = "31/07/2004-10:00-Log entry";
            String entry2 = "15/07/2004-09:00-Another log entry";
            String entry3 = "15/07/2004-08:15-Another log entry from earlier the same day";

            java.util.Vector v = new java.util.Vector();
            v.add(new LogEntry(entry1));
            v.add(new LogEntry(entry2));
            v.add(new LogEntry(entry3));

            java.util.Collections.sort(v);
            System.out.println(v);

            javax.swing.JFrame frame = new javax.swing.JFrame();
            frame.setDefaultCloseOperation(javax.swing.JFrame.EXIT_ON_CLOSE);
            javax.swing.DefaultComboBoxModel model = new javax.swing.DefaultComboBoxModel(v);
            javax.swing.JList list = new javax.swing.JList(model);
            frame.getContentPane().add(list, java.awt.BorderLayout.CENTER);
            frame.setSize(100, 100);
            frame.setVisible(true);

      }

}
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Author Comment

by:adrianjohnson
ID: 11684376
Thanks for the entries so far. I'm a little busy at the moment, but will try them and see what happens.

Adrian Johnson
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Expert Comment

by:Mayank S
ID: 11687579
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Author Comment

by:adrianjohnson
ID: 11706822
I'm working through your code, CEHJ, and changed the name of the main function to DisplayLog.  Having problems calling it, though, from another class:

LogEntry logscreen = new LogEntry();
logscreen.DisplayLog();

The error I get is "The contructor LogEntry is undefined". Is it something I'm missing/doing wrong? It's probably my understanding (it's very hot here in the UK, and I can't concentrate!).

Thanks,

Adrian Johnson
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LVL 92

Expert Comment

by:objects
ID: 11710579
try:

LogEntry.DisplayLog();

You can sort your entries with or without using a seperate class to represent an entry.
The key is using the sort() method and providing a method to handle xomparing two entries.
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Expert Comment

by:Mayank S
ID: 11712838
If you have provided a parameterized constructor in the LogEntry class, then you will need to give a default constructor (with no parameters) too, otherwise you cannot instantiate it without arguments, like:

LogEntry logscreen = new LogEntry () ;

If the DisplayLog () method is still static, you don't need an object for calling it and you can do it directly using the class-name, like objects has shown.
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Expert Comment

by:Mayank S
ID: 11712848
objects, are you still listening to: http://www.experts-exchange.com/Programming/Programming_Languages/Java/Q_21080150.html ?

CEHJ, can I have some inputs from you on that one please, if you want to say something?
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Author Comment

by:adrianjohnson
ID: 11713669
Now I'm getting confused, as it appears I'm getting two different methods of calling the class (and neither of them work).  I renamed the main function DisplayLog(), so it looks like:

public void DisplayLog() {

          String entry1 = "31/07/2004-10:00-Log entry";
          String entry2 = "15/07/2004-09:00-Another log entry";
          String entry3 = "15/07/2004-08:15-Another log entry from earlier the same day";

          java.util.Vector v = new java.util.Vector();
          v.add(new ScreenDisplay(entry1));
          v.add(new ScreenDisplay(entry2));
          v.add(new ScreenDisplay(entry3));

          java.util.Collections.sort(v);
          System.out.println(v);

          javax.swing.JFrame frame = new javax.swing.JFrame();
          frame.setDefaultCloseOperation(javax.swing.JFrame.EXIT_ON_CLOSE);
          javax.swing.DefaultComboBoxModel model = new javax.swing.DefaultComboBoxModel(v);
          javax.swing.JList list = new javax.swing.JList(model);
          frame.getContentPane().add(list, java.awt.BorderLayout.CENTER);
          frame.setSize(100, 100);
          frame.setVisible(true);

     }

How Do I call it from another function in another class?  If I use mayankealges code, I get "The Constructor LogEntry is undefined".  If I use objects code, I get "The method DisplayLog is not static".

Remember, I'm fairly new to Java (and baking hot here in the UK), so you need to be really specific.

Thanks,

Adrian Johnson
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LVL 92

Assisted Solution

by:objects
objects earned 100 total points
ID: 11713683
> public void DisplayLog() {

make it static:

public static void DisplayLog() {
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Author Comment

by:adrianjohnson
ID: 11713703
D'oh!

Thanks Objects.  Sorry I'm so dim, but that worked a treat!


Adrian Johnson
0
 
LVL 86

Expert Comment

by:CEHJ
ID: 11716067
8-)
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LVL 92

Expert Comment

by:objects
ID: 11722332
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