Java Data Structure How to - Sort List by element count

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Question

We would like to know how to sort List by element count.

Answer

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
/*  w w  w.j av  a 2  s  .  c o  m*/
public class Main {
  public static void main(final String[] args) {
    final List<String> asu = new ArrayList<String>();
    asu.add("2");
    asu.add("11");
    asu.add("7");
    asu.add("10");
    asu.add("7");
    asu.add("12");
    asu.add("2");
    asu.add("11");
    asu.add("11");
    asu.add("7");
    asu.add("7");
    asu.add("7");

    List<String> list = new ArrayList<String>();
    Map<String, Integer> counts = new HashMap<String, Integer>();
    list.addAll(asu);
    for (String item : list) {
      Integer count = counts.get(item);
      if (count == null) {
        count = 1;
      } else {
        count = count + 1;
      }
      counts.put(item, count);
    }
    Collections.sort(asu, new Comparator<String>() {
      @Override
      public int compare(final String left, final String right) {
        int result = counts.get(left).compareTo(counts.get(right));
        if (result == 0) {
          result = left.compareTo(right);
        }
        return result;
      }
    });
    System.out.println(asu);
  }
}

The code above generates the following result.

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