Code Recipes Blog

In this post under Apache Collections, I will explain with example, the purpose of CollectionUtils “getCardinalityMap” method.

This method takes a collection as an argument and returns a map.

A map where key is an element from the collection, and value will be the number of times the element is repeated in the collection.

So if a list contain below elements.

1
2
2
3
3
3

The output will be a map with below contents

Key --> Value
1     --> 1
2     --> 2
3     --> 3

In this way CollectionUtils “getCardinalityMap” is used.

Below is the complete main code for your reference

Main class

package defaultPackage;

import org.apache.commons.collections4.CollectionUtils;

import java.util.ArrayList;
import java.util.List;
import java.util.Map;

public class Example11 {
    public static void main(String[] args) {
        List<Integer> intList = new ArrayList<>(0);

        intList.add(1);
        intList.add(2);
        intList.add(2);
        intList.add(3);
        intList.add(3);
        intList.add(3);

        Map<Integer, Integer> cardinalityMap = CollectionUtils.getCardinalityMap(intList);

        for(Map.Entry<Integer, Integer> entry : cardinalityMap.entrySet()) {
            System.out.println(entry.getKey() + ":" + entry.getValue());
        }
    }
}