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how to sort ArrayList based on its objects? (Read 798 times)

Eric F. Junior Member Offline Posts: 56	how to sort ArrayList based on its objects? Feb 22^nd, 2009, 8:13am I have an ArrayList with custom objects in them. How do I sort the list by the contents of one variable in the objects? e.g. objects are of class TimePoint() with properties .time and .type. i want to sort the ArrayList of TimePoints by time.
	http://www.ericforman.com

bootleg

Re: how to sort ArrayList based on its objects?
Reply #1 - Feb 22^nd, 2009, 9:28am

There are several ways to do this:

(1) Override the compateTo method or and use Collections.sort(<List>)

(2) Write a Comparator [1] and override the equals method and use Collections.sort(<List>, <Comparator>) [2]

If you want to use data types, which uses the hashCode method (like HashSet/HashMap), you should take care to be consistent with the hashCode method [3].

Some links:
[1] http://java.sun.com/javase/6/docs/api/java/util/Comparator.html
[2] http://java.sun.com/j2se/1.4.2/docs/api/java/util/Collections.html#sort%28java.util.List,%20java.util.Comparator%29
[3] http://www.geocities.com/technofundo/tech/java/equalhash.html

PhiLho YaBB Moderator Offline Posts: 4190 Near Paris (France)	Re: how to sort ArrayList based on its objects? Reply #2 - Feb 22^nd, 2009, 10:26am See also sort array of objects by String inside variable thread. Principles are the same for arrays and collections.

Eric F. Junior Member Offline Posts: 56	Re: how to sort ArrayList based on its objects? Reply #3 - Feb 23^rd, 2009, 2:08am thanks both, option 1 and that referenced thread did the job quickly. will read those docs someday...
	http://www.ericforman.com

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