Maps with multiple types of values in java

Question

I have to accomplish a strange peculiar scenario. Its described as follows:

I have to design a Map where the \'Keys\' are always of String

Answer 1

Of course there is. Pick your poison:

Map<String, Object> mixed = new HashMap<String, Object>();

Map<String, Serializable> mixed = new HashMap<String, Serializable>();

@SuppressWarnings("rawtypes")
Map mixed = new HashMap();

Answer 2

It is possible to do something like Map<String, Object>.

But: I would strongly suggest to think your design over. You should use a class for your persons instead. That way you could do: Map<String, Person> with Person having getters and setters for names, phone numbers and other information.

Example Person class:

public class Person {

    private String name;
    private List<String> phoneNumbers = Collections.emptyList();

    public void setName(String name) {
        this.name = name;
    }

    public String getName() {
        return name;
    }

    public void setPhoneNumbers(List<String> phoneNumbers) {
        this.phoneNumbers = phoneNumbers;
    }

    public void addPhoneNumber(String number) {
        phoneNumbers.add(number);
    }

    public List<String> getPhoneNumbers() {
        return phoneNumbers;
    }
}

Answer 3

I would do one of the following:

1. Use a Multimap<String, String>. The Multimap would contain one or more values associated with each key.

2. Use a Map<String, Either<String, List<String>>>. Use a Either to distinguish between a single or multiple values.

Answer 4

Well, why not make a Map<String, List<String>>? you could always just add one element to your list if there is just one value or use a common supertype of String and List, thus you would get

Map<String, Object>

Answer 5

Why not make a PhoneNumber wrapper class that exposes an API for soring either one or multipel phone numbers and then can retrieve either one or all (multiple) phone numbers and then make a map of String and PhoneNumber? Something like:

class PhoneNumber {


  private String[] phoneNumbers;


  public void storePhoneNumber(String... phoneNumbers) {
     this.phoneNumbers = phoneNumbers;
  }

  public String getPhoneNumber() {
    if(phoneNumbers.length>=1) {
      return phoneNumbers[0];
    } else {
      return null;
    }

  }

  public List<String> getPhoneNumbers() {
    if(phoneNumbers!=null) {
      return Arrays.asList(phoneNumbers);
    } else {
      return null;
    }

  }

}