CODEWITHSUNDEEP
javagroovycollections
kandarp
kandarp

Reputation: 1101

Difference between MAP in Groovy and Java

Currently, we are using Groovy as frontend and Java Spring as backend.

In groovy we define a property Map parameters = [:] which will assign to private Map<String, Object> parameters; in Java.

I have a question regarding the instance of this MAP interfaces in both languages. As I read groovy create by default instance of LinkedHashMap and Java create by default instance of HashMap is it true?

My overall requirement is to preserve the order of data, which LinkedHashMap does but HashMap not.

So as frontend is already LinkedHashMap, it will pass ordered data into the backend.

public void setParameters(Map<String, Object> parameters) {
    this.parameters = parameters;
}

Is it true? Do I need to change model in JAVA (backend) from Map to LinkedHashMap?

Upvotes: 1

Views: 1588

Answers (2)

cfrick
cfrick

Reputation: 37008

Map is an interface. So if you demand a Map as argument or parameter, you are only requesting those guarantees.

If you demand further guarantees (e.g. that LinkedHashMap preserve insertion order), then you are better off requesting that explicitly.

Since you are talking "backend" and "frontend" there is also the matter of transport between the two. If you are using transports (and not direct calls), that are no able to hold order in maps (e.g. JSON), then you are better off to not rely on the different data types. E.g. use a list of key-value tuples instead.

Side note about the defaults

Groovy has a literal to quickly create maps ([:] or forms with keys like [a: 42]). Those maps are LinkedHashMap as you stated.

groovy:000> [:].getClass()
===> class java.util.LinkedHashMap

Since Java as of up to 15 has no literal for maps there is no "default" -- the default is what you make it.

In general it's best to always think about the data type you are actually in need of. This also means, that the map literal of Groovy can be the wrong choice.

Upvotes: 1

ernest_k
ernest_k

Reputation: 45319

As I read groovy create by default instance of LinkedHashMap and Java create by default instance of HashMap is it true?

Java, in fact, doesn't create any kind of map by default. The developer picks which Map implementation they instantiate (almost always). Java doesn't have a counterpart for Groovy's map literal [:], so there's no "default" type to instantiate in Java. As for Groovy, it's true that the map literal creates a LinkedHashMap:

groovy:000> [:].getClass()
===> class java.util.LinkedHashMap

So as frontend is already LinkedHashMap, it will pass ordered data into the backend. [...] is it true?

Yes. During runtime, the Map object that's passed to setParameters() will be as generated by your "front-end" code. The call would simply behave the same way as though you'd created a LinkedHashMap from your Java code and passed it to the method. The runtime won't re-shape the object into a HashMap (even if it had to do something like that, making it a HashMap would be curiously arbitrary). All that matters here is that the types are compatible, and LinkedHashMap is a Map.

Upvotes: 3

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