Re: A suitable container that can sort -- please help!

Eric Sosman <>
Tue, 07 Jul 2009 10:58:48 -0400
<1246978728.712629@news1nwk> wrote:

On Jul 7, 2:52 pm, Simon <> wrote:

   I need an object that can contain several hundred: Point objects and
their a corresponding double. I then need to be able to sort on the
double and then jump accross and grab the Point.

Any implementation of SortedSet [1], e.g TreeSet [2], together with a
suitable implementation of Comparator that compares your Point instances
should do the job. You can use the last() of a headSet() or the first()
of a tailSet() to jump close to a particular point.

Just as an aside: For sorting points you have to define some relation,
e.g. "left-of" or "above" or "has greater norm". In Java, this is done
by the Comparator. I'm not sure what you mean by "corresponding double",
but it might be that none of the above is useful in your case and you
might be better off using a specialized geometric data structue, which
you probably have to implement yourself or take from a library.



Hi Simon,

   You mean something liek:

SortedSet set = new TreeSet();

set.add(SomePoint, somedouble)

     This won't work. The SortedSet contains instances of "something,"
not pairs of instances. If you need to associate a Point with a double,
one straightforward approach is to make yourself a "holder" class that
contains the Point and its associated double, and to put instances of
the "holder" into the set:

    class Holder {
        final Point point;
        final double value;
        Holder(Point point, double value) {
            this.point = point.clone();
            this.value = value;
    set.add(new Holder(somePoint, someDouble));


then extract first object?

     If all you want is the first Point/double pair in sorted order,
keeping the entire collection sorted is a lot of wasted work. Some

     - If you want only the extreme Point/double pair, just dump all
       the pairs into any convenient collection without regard to their
       order. Then when you want the extreme, just sweep once over the
       collection to find the pair with minimum (or maximum) value.

     - If you gather all the Point/double pairs and then want to process
       them in sorted order, begin by putting them in a List without
       regard to order. When you've gathered them all, sort the List
       with Collections.sort(), and then traverse the sorted List.

     - If Point/double pairs are coming and going all the time and you
       need to keep them in sorted order all the time, the extra work
       of a SortedSet makes sense. Note that a SortedSet is a Set and
       thus allows no duplicates; you can skirt this issue if need be
       by letting your Holder class inherit the equals() method from
       Object (so no two Holders will be "equal" even if they happen
       to have equal Points and doubles).


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