How to create a Map in java with two keys and a list of values

Question

Wants to create a map with two keys and values as a list. Could you please help me with a sample code for the same

Possible duplicate of [HashMap with multiple values under the same key](https://stackoverflow.com/questions/4956844/hashmap-with-multiple-values-under-the-same-key) — tobsob, Oct 25 '19 at 06:38
It is not clear if you want a map with two objects as key or one with two keys, which would mean just two entries... What is it? — deHaar, Oct 25 '19 at 06:44
two keys == two maps ?? or do you mean a key with two values/fields? — user85421, Oct 25 '19 at 07:23
I guess you want something like this: https://stackoverflow.com/questions/14677993/how-to-create-a-hashmap-with-two-keys-key-pair-value — sanastasiadis, Oct 25 '19 at 07:31

score 1 · Answer 1 · edited Oct 25 '19 at 07:29

I think you need something like this:

Firstly you need a POJO which contains your composite key, and to avoid messing up the KeySet inside the map, that pojo must implements equals and hashcode

import java.util.Objects;

public class MyKey {  
    private final String firstKeyAttr;
    private final Integer secondKeyAttr;

    public MyKey(String firstKeyAttr, Integer secondKeyAttr) {
        this.firstKeyAttr = firstKeyAttr;
        this.secondKeyAttr = secondKeyAttr;
    }

    public String getFirstKeyAttr() {
        return firstKeyAttr;
    }

    public Integer getSecondKeyAttr() {
        return secondKeyAttr;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        MyKey myKey = (MyKey) o;
        return Objects.equals(firstKeyAttr, myKey.firstKeyAttr) &&
                Objects.equals(secondKeyAttr, myKey.secondKeyAttr);
    }

    @Override
    public int hashCode() {
        return Objects.hash(firstKeyAttr, secondKeyAttr);
    }
}

And then, you can create a map in this way:

public static void main(String[] args) {
   Map<MyKey, List<Object>> myMap = new HashMap<>();
   myMap.put(new MyKey("key1", 1), Collections.singletonList(1));
   ...
}

How to create a Map in java with two keys and a list of values

1 Answers1