Menu
I'm recently into Rest API in java and came across MultivaluedMap. I don't find the advantage MultivaluedMap over HashMap or other classes like TreeMap or LinkedHashMap.Please explain the scenario when MultivaluedMap is necessary.
772
A map cannot contain duplicate keys; each key can map to at most one value. So in a MultivaluedMap you can insert 0, 1, 2, 3 or more objects related to the same key. In a Map you can insert exactly 1 object related to a key.
A MultiValuedMap is a Map with slightly different semantics: Putting a value into the map will add the value to a Collection at that key. Getting a value will return a Collection , holding all the values put to that key.
Whereas, ConcurrentHashMap is introduced as an alternative to the HashMap. The ConcurrentHashMap is a synchronized collection class. The HashMap is non-thread-safe and can not be used in a Concurrent multi-threaded environment.
HashMap is faster than Map since it does not keep track of the order in which its components are inserted. HashMap, unlike Map, can hold duplicate values. It's feasible to use the Map interface implementing classes to implement it. HashMap, on the other hand, is all about implementing the Map interface.
A MultivaluedMap is:
A map of key-values pairs. Each key can have zero or more values.
A Map is:
An object that maps keys to values. A map cannot contain duplicate keys; each key can map to at most one value.
So in a MultivaluedMap you can insert 0, 1, 2, 3 or more objects related to the same key.
In a Map you can insert exactly 1 object related to a key.
This is the difference, it can be useful if you need to store many values related to a single key, if you have only one value they are similar.
A possibile scenario is a Dictionary where you save all the words related starting with a letter. The keys are A B C... Z and the values are the words.
A -> Acid
Apple
August
B -> Banana
Boat
C -> Car
Chain
...
Z -> Zebra
That can be coded with:
MultivaluedMap<String, String> multiMap = new MultivaluedHashMap<>();
multiMap.add("A", "Acid");
multiMap.add("A", "Apple");
multiMap.add("A", "August");
multiMap.add("B", "Banana");
multiMap.add("B", "Boat");
multiMap.add("C", "Car");
multiMap.add("C", "Chain");
multiMap.add("Z", "Zebra");
Another scenario is a Map holding all products buyed by a user. The keys are the user id and values are the products.
USER1 -> Pizza Margherita
Pizza Pepperoni
USER2 -> Pizza Margherita
USER3 -> Pizza Margherita
Pizza Pepperoni
Pizza Four Cheese
If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With
