Hash Map with LinkedList in java

Question

Is there a built in implementation in java for hash map whose values are linked lists?

like, if I put:

 map.put(1, "A");
 map.put(1, "B");

then it automatically add A and B to the linked list. When I retrieve from the map, as:

  map.get(1)

I get back a list containing both of them?

Community · Accepted Answer · 2020-06-20 09:12:55Z

4

Java does not have it but you can use MultiMap from Google Guava.

A collection similar to a Map, but which may associate multiple values with a single key. If you call put(K, V) twice, with the same key but different values, the multimap contains mappings from the key to both values.

The methods get(K), keySet(), keys(), values(), entries(), and asMap() return collections that are views of the multimap

This article Multimaps - Google Guava gives you complete idea about how to use it and also how to do it with HashMap using List as value.

edited Jun 20, 2020 at 9:12

CommunityBot

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answered Nov 2, 2012 at 19:38

Amit Deshpande

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kosa · Accepted Answer · 2012-11-02 19:38:20Z

2

Second put will overwrite first put. You will get B as response.

As per javadoc

If the map previously contained a mapping for the key, the old value is replaced

If you want to keep both entries, you need to use thrid party library google guava MultiMap

answered Nov 2, 2012 at 19:38

kosa

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Comments

Frank · Accepted Answer · 2012-11-02 19:39:14Z

1

Nope, just build your own.

First you take a HashMap, if the key does not exist you put the linkedList in...

Simple...

answered Nov 2, 2012 at 19:39

Frank

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