need advise with calender/date specefic thing

Programming Questions

clankill3r

need advise with calender/date specefic thing

in Programming Questions • 1 years ago

I have a list of fatalities that happen during 2 years. Sometimes there are days that there happened nothing and sometimes 10 things a day.

I would like to get them by month for example. Or get them all from a certain year.

Like now i'm working like:

class Year {

ArrayList<Month> months = ...

and a class for months, and for days.

But this way if i want to move something to the next day wich happens to be the next month for example would be a hell.
On stackoverflow i read a lot of things like "extending Calendar is a bad idea". But i didn't found a good solution for what i want so does anyone have suggestions?

Replies(8)

kritzikra..

Re: need advise with calender/date specefic thing

1 years ago

first of all: sorry for my long answer.

i'm not quite sure i even understood your question properly,

but i started writing and it got very long. really hope this helps :)

so, here it is:

--- - -- - - -

sounds like you're working with a very small amount of data.

easiest strategy would then be to just keep them all in one messy list

(maybe only sorted by date) and to then formulate queries, i.e. filtering

out the ones you want.

say you have the following data structure:

class Fatality{
GregorianCalendar cal; // use this instead of Date, much more handy!
// all your other fields go here ...
}
ArrayList<Fatality> fatalities;
void setup(){
size( ... );
loadFatalities( ... );
}

now, you'll need a few helpers to work with this nicely:

public interface FatalityFilter{
public boolean matches( Fatality f );
}
public ArrayList<Fatality> filter( FatalityFilter filter ){
ArrayList<Fatality> results = new ArrayList<Fatality>();
for( Fatality f : fatalities ){
if( filter.matches( f ) ){
results.add( f );
}
}
}

so the idea is to have filters and a filter function.

you'd have an active subset which you're currently working with,

and each time you want a different dataset you'd simply run a filter against the entire dataset,

then store the result.

a very simplified example:

switch to using all fatalities that occured on a monday, when the user presses 'm' ...

import static java.util.GregorianCalendar.*; // not necessary, but makes your life a lot easier :)
ArrayList<Fatalities> fatalities; // all fatalities
ArrayList<Fatalities> activeSet; // the subset we're currently looking at
// ....
void keyPressed(){
if( key == 'm' ){
// query the entire set, filter the ones that match and store the result ...
activeSet = filter( new FatalityFilter(){
public boolean matches( Fatality f ){
return f.cal.get( DAY_OF_WEEK ) == MONDAY;
}
} );
}
}

clankill3r

Re: need advise with calender/date specefic thing

1 years ago

Answers aren't fast to long.

Since i allready have a lot of code in Eclipse i thought let's try your thing in a simple processing sketch first.

I fixed most of your code mistakes, i'm only stuck at the filter point.
This is the error:
Cannot find a class or type named "filter"

this is the code:

import java.util.GregorianCalendar.*; // no static!
ArrayList<Fatality> fatalities; // all fatalities
ArrayList<Fatality> activeSet; // the subset we're currently looking at
String[] someDates = {
"7/2/2011",
"7/3/2011",
"7/4/2011",
"7/5/2011",
"7/6/2011",
"7/6/2011",
"7/7/2011",
"7/7/2011",
"7/8/2011",
"7/8/2011",
"7/8/2011",
"7/9/2011",
"7/9/2011",
"7/10/2011",
"7/10/2011",
"7/11/2011",
"7/11/2011",
"7/11/2011",
"7/12/2011",
"7/12/2011",
"7/12/2011",
"7/12/2011",
"7/13/2011",
"7/13/2011",
"7/14/2011",
"7/14/2011",
"7/15/2011",
"5/1/2011",
"6/1/2011",
"6/9/2011",
"6/23/2011",
"7/6/2011",
"7/10/2011",
"7/12/2011"
};
void setup() {
size( 200, 200);
fatalities = new ArrayList<Fatality>();
activeSet = new ArrayList<Fatality>();
// create some fake fatalitys
for (int i = 0; i < someDates.length; i++) {
Date date = StringToDate(someDates[i], "MM/dd/yyyy");
fatalities.add(new Fatality(date));
}
}
void draw() {
}
void keyPressed() {
if ( key == 'm' ) {
// query the entire set, filter the ones that match and store the result ...
activeSet = filter( new Filter() { // Cannot find a class or type named "filter"
public boolean matches( Fatality f ) {
return f.cal.get( DAY_OF_WEEK ) == MONDAY;
}
}
);
for(int i = 0; i < activeSet.size(); i++) {
Fatality f = activeSet.get(i);
println(f.calendar);
}
}
}
class Fatality {
//GregorianCalendar cal; // use this instead of Date, much more handy!
Calendar calendar = new GregorianCalendar();
Fatality(Date date) {
calendar.setTime(date);
}
}
public interface FatalityFilter {
public boolean matches( Fatality f );
}
public ArrayList<Fatality> filter( FatalityFilter filter ) {
ArrayList<Fatality> results = new ArrayList<Fatality>();
for ( Fatality f : fatalities ) {
if ( filter.matches( f ) ) {
results.add( f );
}
}
return results;
}
public static Date StringToDate(String date, String format) {
if (date.equals("null") == false) {
DateFormat stampFormat = new SimpleDateFormat(format);
try {
return stampFormat.parse(date);
}
catch (ParseException e) {
//die("Problem with dates", e);
PApplet.println("die");
}
}
return null;
}

kritzikra..

Re: Re: need advise with calender/date specefic thing

1 years ago

this was of course a stupid mistake of me,

it should have meant

new FatilityFilter(){
// ...
}

instead :)

tiny remark:

many people would write

! "null".equals( date )
// instead of:
date.equals( "null" ) == false

whether you write ! .... or == false doesn't matter so much,

but putting the constant string "null" in the front works even if the

date string is null (actually null, not just for the string "null")

otherwise you get a nullpointerexception.

about the import:

nope, this was written as

import static java.util.GregorianCalendar.*;

on purpose.

with the static keyword it means: import all static constants and methods

without the static keyword it means: import all subclasses.

the first allows you to write MONDAY instead of GregorianCalendar.MONDAY,

while the second doesn't ...

doesn't really matter either, just a handy shortcut.

(if it doesn't work you're maybe still compiling for java 1.5)

best,

hansi.

(p.s. i'm on irc right now if you have any quick questions...)

clankill3r

Re: need advise with calender/date specefic thing

1 years ago

cool, it works now :)
And a few good lessons, thanks for that :) Do you reccomand any books or any?

And i think i run java 1.5.

Also monday work's fine, i only have to use it by DAY_OF_WEEK

return f.calendar.get( GregorianCalendar.DAY_OF_WEEK ) == MONDAY;

P.s. i found you filter hard to understand (as in if i had to reconstruct it myself or explain how it works).

kritzikra..

Re: need advise with calender/date specefic thing

1 years ago

cool that you got it to work :)

books: not reading many books on coding anymore. but if programming interests you: 1.) look at different languages, especially the ones that feel very distant but don't completely bemuse you; and 2.) read and modify other people's code.

a few words on the filter:

yes, it feels stupid and complicated. find an easier, but less flexible version below.
if you know sql this is the same as doing SELECT * FROM mytable WHERE someField = someValue;
if you know jquery it is like the .filter function, e.g. $( "p" ).filter( ":visible" )
filtering is a standard construct of what is called "functional programming",
in practice this means you're thinking more about sets of things than about individual things,
this usually involves passing around lots of function, like the filter function in this case
(hence the name functional programming :) ).
i'm quite certain this functionality will be included by default as soon as java 8 comes out
speaking of: please upgrade your jdk, version 1.5 is really really really really really old now.

alright, enough advice.

to make the confusion perfect, below is a snippet of code that does the same, but you might find it easier to understand:

ArrayList<Fatality> fatalities;
ArrayList<Fatality> activeSet;
// ...
void setup(){
// ... yes yes, everything normal here ...
}
void keyPressed(){
if( key == 'a' ) activeSet = filterBy( "mondays" );
if( key == 'b' ) activeSet = filterBy( "firstOfMonth" );
// ... and so on ...
}
ArrayList<Fatality> filterBy( String what ){
ArrayList<Fatality> result = new ArrayList<Fatality>();
// walk through ALL fatalities
for( Fatality f : fatalities ){
// if the criterion is monday:
if( "mondays".equals( what ) )
if( f.cal.get( DAY_OF_WEEK ) == MONDAY ) result.add ( f );
if( "firstOfMonth" ).equals( what ) )
if( f.cal.get( DAY_OF_MONTH ) == 1 ) result.add( f );
// and so on ... put all your rules here ...
}
return result;
}

good luck with your project,

it sounds dangerous :)

best,

hansi.

clankill3r

Re: need advise with calender/date specefic thing

1 years ago

thanks,

for the purpose of learning i use the complex method.

---

First of all, with what i had i had the days sorted on date. However by 06-2010 for example there is kinda a gap because a lot of data is missing.

So i prefer to loop threw every date that existed between the firstDate and lastDate i got. How can i do that? I do know those 2 dates (for loop).

p.s. i'm really tired so you meight have seen some stupid questions here before that i solved myself now.

clankill3r

Re: need advise with calender/date specefic thing

1 years ago

First i didn't want to move to Joda Time cause i like to learn java's default classes first. But Joda made things so much easier for me, i deleted 2 classes now and about 50 lines of code on other places :)

Also in case someone needs to loop with time in joda:

for(DateTime iDate = firstDate; iDate.isBefore(lastDate); iDate = iDate.plusDays(1)) {
{
...
}

(where firstDate and lastDate is a DateTime object aswell)

kritzikra..

Re: need advise with calender/date specefic thing

1 years ago

hey!

ah, looks like you solved it yourself already.

jodatime is nice i guess, but greogriancalendar has very similar functionality.

also i think you slightly missed the point of the filters, which is not having

to rewrite the same for-loops over and over :)

here's what i would have done:

// use this function from anywhere to get all fatalities within two dates
ArrayList<Fatality> filterByInterval( final GregorianCalendar start, final GregorianCalendar end ){
return filter( new FatalityFilter(){
public boolean matches( Fatality f ){
// allow an entry only if start < f.cal < end
return start.before( f.cal ) && f.cal.before( end );
}
} );
}