CODEWITHSUNDEEP
javasortingcollectionsstring-comparisontreemap
d0pe
d0pe

Reputation: 583

Sort Map<String, Object> by keys with IgnoreCase?

Well, I tested TreeMap but it doesn't take in account IgnoreCase on string comparision. I need to order lexicographically and ignoring case. Is there any other way?

Thanks, that works (TreeMap (Comparator c)). However, I have another question:

public final Comparator<Object> STR_IGN_CASE_COMP = new Comparator<Object>() {

    public int compare(Object h1, Object h2) {
            String s1 = h1.getId();
            String s2 = h2.getId();
            return s1.compareToIgnoreCase(s2);
    }
}; //STR_IGN_CASE_COMP

How can I universialize the comparator to work with different objects? assuming all have the getId() method.

Thanks, Martin

Upvotes: 10

Views: 11442

Answers (7)

Jeff Paquette
Jeff Paquette

Reputation: 7127

I suspect that you should construct your TreeMap with a custom comparator. 

import java.text.Collator;
import java.util.Comparator;

class IgnoreCaseComp implements Comparator<String> {
  Collator col;

  IgnoreCaseComp() {
    col = Collator.getInstance();

    col.setStrength(Collator.PRIMARY);
  }

  public int compare(String strA, String strB) {
    return col.compare(strA, strB);
  }
}

Upvotes: 0

camickr
camickr

Reputation: 324147

How can I universialize the comparator to work with different objects? assuming all have the getId() method.

You should be able to use a BeanComparator.

Upvotes: 1

Michael Brewer-Davis
Michael Brewer-Davis

Reputation: 14276

You want to use a Comparator in the TreeMap constructor. In particular, look at String.CASE_INSENSITIVE_ORDER.

TreeMap map = new TreeMap(String.CASE_INSENSITIVE_ORDER);

Using Collator or a custom Comparator may work better for you in a non-English locale or if you need more complex ordering.

Upvotes: 37

dustmachine
dustmachine

Reputation: 10824

Yes, what you want is to use the TreeMap constructor that takes a Comparator. Make a comparator that uses compareToIgnoreCase.

Upvotes: 0

Chi
Chi

Reputation: 23174

The best way would be to use a Collator. A collator is a built in class, which also implements Comparable, and therefore you can use it for your TreeMap.

With a collator, you can also control the strength of the comparision, for example, if you want to be accent-insensitive as well.

Collator stringCollator = Collator.getInstance();
stringCollator.setStrength(Collator.PRIMARY); 
new TreeMap<String, String>(stringCollator)

Upvotes: 8

shoover
shoover

Reputation: 3140

If you had a list, I would say try Collections.sort() with a Comparator. You may have to roll your own Comparator that uses String.equalsIgnoreCase() instead of equals().

public static <T> void sort(List<T> list,
                        Comparator<? super T> c)

But I was on the right track. Try the TreeMap constructor that takes a Comparator:

public TreeMap(Comparator<? super K> comparator)

Upvotes: 0

Murali VP
Murali VP

Reputation: 6427

Provide it a Comparator that compares strings case ignored.

TreeMap(Comparator c)

Upvotes: 1

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