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Sort list of complex objects alphabetically

Posted on 2009-12-16
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Last Modified: 2012-05-08
Hi,

I need to sort a list of complex objects. Looks like this:

  class Farm {
     String name;
     Data mLotsOfData;
  }

  List<Farm> farms = getAllFarms();

  // Now i want to build a new alphabetical list.
  TreeMap<String, Farm> alpha = new TreeMap<String, Farm>();
  for (all farms) {
      alpha.put(farms.get(i).name, farms.get(i));
  }

  // Back to a list.
  ArrayList<Farm> alphaFarms = new ArrayList<Farm>();
  for (all in alpha) {
      alphaFarms.add(it.getValue());
  }

but it seems to not do anything -what's the right way to do this?

Thanks
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Question by:DJ_AM_Juicebox
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Author Comment

by:DJ_AM_Juicebox
ID: 26068378
Nevermind, that does work (was using package names or something for Farm.name).

But is there a more efficient way?

Thanks
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LVL 23

Expert Comment

by:cmalakar
ID: 26068382
You need to pass a comparator to the TreeMap object constructor.
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LVL 23

Expert Comment

by:cmalakar
ID: 26068395
Sorry... didn't check String is key..

Thats the right way
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LVL 23

Accepted Solution

by:
cmalakar earned 2000 total points
ID: 26068406
>>   // Back to a list.

Can be done directly like..

treeMap.keySet( ), will give you a Set Object with all the keys.
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LVL 23

Expert Comment

by:cmalakar
ID: 26068417
Moreover .. if you have getAllForms() source code..

You can modify directly that to return a Map.. (an instance of TreeMap)
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