HashMap with multiple values under the same key

Question

Is it possible for us to implement a HashMap with one key and two values. Just as HashMap?

Please do help me, also by telling (if there is no way) any other way to implement the storage of three values with one as the key?

Answer 1

Yes, this is frequently called a multimap.

See: http://google-collections.googlecode.com/svn/trunk/javadoc/index.html?com/google/common/collect/Multimap.html

Answer 2

If you use Spring Framework. There is: org.springframework.util.MultiValueMap.

To create unmodifiable multi value map:

Map<String,List<String>> map = ...
MultiValueMap<String, String> multiValueMap = CollectionUtils.toMultiValueMap(map);

Or use org.springframework.util.LinkedMultiValueMap

Answer 3

The easiest way would be to use a google collection library:

import com.google.common.collect.ArrayListMultimap; import com.google.common.collect.Multimap;

public class Test {

public static void main(final String[] args) {

    // multimap can handle one key with a list of values
    final Multimap<String, String> cars = ArrayListMultimap.create();
    cars.put("Nissan", "Qashqai");
    cars.put("Nissan", "Juke");
    cars.put("Bmw", "M3");
    cars.put("Bmw", "330E");
    cars.put("Bmw", "X6");
    cars.put("Bmw", "X5");

    cars.get("Bmw").forEach(System.out::println);

    // It will print the:
    // M3
    // 330E
    // X6
    // X5
}

}

maven link: https://mvnrepository.com/artifact/com.google.collections/google-collections/1.0-rc2

more on this: http://tomjefferys.blogspot.be/2011/09/multimaps-google-guava.html

Answer 4

I use Map<KeyType, Object[]> for associating multiple values with a key in a Map. This way, I can store multiple values of different types associated with a key. You have to take care by maintaining proper order of inserting and retrieving from Object[].

Example: Consider, we want to store Student information. Key is id, while we would like to store name, address and email associated to the student.

       //To make entry into Map
        Map<Integer, String[]> studenMap = new HashMap<Integer, String[]>();
        String[] studentInformationArray = new String[]{"name", "address", "email"};
        int studenId = 1;
        studenMap.put(studenId, studentInformationArray);

        //To retrieve values from Map
        String name = studenMap.get(studenId)[1];
        String address = studenMap.get(studenId)[2];
        String email = studenMap.get(studenId)[3];

Answer 5

I prefer the following to store any number of variables without having to create a separate class.

final public static Map<String, Map<String, Float>> myMap    = new HashMap<String, Map<String, Float>>();

Answer 6

Here is THE ANSWER : ) : )

String key= "services_servicename"

ArrayList data;

for(int i = 0; i lessthen data.size(); i++){

        HashMap<String, String> servicesNameHashmap = new HashMap<String, String>();
        servicesNameHashmap.put(key,data.get(i).getServiceName());
        mServiceNameArray.add(i,servicesNameHashmap);   }

I have got the Best Results.

You Just Have to Create New HashMap Like

HashMap servicesNameHashmap = new HashMap();

in Your For Loop. It will have Same Effect Like Same Key And Multiple Values.

Happy Coding :)