There is a Java utility class called Arrays that has a sort() method that will do what you want.

http://java.sun.com/j2se/1.4.2/docs/api/java/util/Arrays.html#sort(java.lang.Object[],%20int,%20int,%20java.util.Comparator)

You would have to write the Comparator class, since it sounds like you aren't sorting by the natural order of the class.

Comparators really aren't that hard to write. You need to create a class that implements the Comparator interface.

Here's some sample code I whipped up to demonstrate.


class A {
 String str;
 // Constructor just sets the value of str
 A(String s) {
   str = s;
 }
 // Returns str
 String getStr() {
   return str;
 }
 // Override toString so the value of str is shown by println()
 String toString() {
   return str;
 }
}

class AComparator implements Comparator {
 int compare(Object o1, Object o2) {
   String str1 = ((A) o1).getStr();
   String str2 = ((A) o2).getStr();
   return str1.compareTo(str2);
 }
}

// Create an array with 3 A objects that are not sorted by the str field
A a1 = new A("abcd");
A a2 = new A("efgh");
A a3 = new A("cdef");
A[] aArray = new A[] {a1, a2, a3};

// Print the array to show array is not in sorted order
println(aArray);
println();

// Sort and print to show array is now sorted by the value of str
Arrays.sort(aArray, new AComparator());
println(aArray);

thanks so much WombatNation! I just finally implemented it and it's working just fine

here's a question about taking it further - say I have sorted my array by a certain attribute but there are other attributes which I would like to sort each of those groupings by would I need to create separate arrays from the first and do another comparator? Is there a way to split the array at the point where the attribute changes?

for a concrete example - I have 70 or so animals and I want to sort by the biome in which they're found - and I have done that easily thanks to your help - but then within each biome(my initial sorting key) within the array I want the animals to be grouped by a diet type( a second layer of sorting), how would I do this...

i tried to use a float comparison instead of the string comparison in the nested check and I got an error:

"Cannot invoke compareTo(float) on the primitive type float"

Quote:


Also, once my array is sorted how do I trigger a different behaviour for a shift in the field value - say I am cycling through my array assigning each a field value but I want something different to happen at each change in the field value I used to sort my data, how would I do this...? I think I may be going about this the wrong way...I am trying to plot out my array objects (animals) in a 2d graph but in such a way so that they do not overlap, and for that I have been using a distinct int count++ for every possible region of the graph so each animal gets neatly plotted one after the next...

how do I fix this? Thanks for your help!

Also, sorry, but I didn't quite follow your second question. Either I'm missing an important piece of context or I've just had too many glasses of Syrah tonight.

oompa_l wrote on Jan 26^th, 2009, 11:14pm:
That means that str1 is null, ie. not initialized. Are you sure all your fields are set correctly

oompa_l wrote on Jan 27^th, 2009, 12:13am:

Just invert the result of the Comparator.
You can do whatever you want here, compare a string starting at nth character or after the nth comma, comparing reversed strings or in case-insensitive way, etc. Just process the strings (or objects) before comparing them.

@Wombat - this is a very useful explanation, thanks.

Quote:


Why is that faster than compareTo?  you mean because you don't have to create objects (i.e. you can use float instead of Float)?

@TVS: curious what your exact Q1 and Q2 were, which you have replaced with "solved," i can guess from the solution update but update Q2 is cryptic.