cast LinkedHashMap to HashMap in groovy

Question

How do I convert LinkedHashMap to java.util.HashMap in groovy?

When I create something like this in groovy, it automatically creates a LinkedHashMap even when I declare it like HashMap h = .... or def HashMap h = ...

I tried doing:

HashMap h = ["key1":["val1", "val2"], "key2":["val3"]]

and

def HashMap h = ["key1":["val1", "val2"], "key2":["val3"]]

h.getClass().getName() still comes back with LinkedHashMap.

Just curious, why do you care what implementation of `Map` it's creating? — Steve Kuo, Sep 23 '10 at 19:25

score 8 · Accepted Answer · answered Sep 23 '10 at 17:30

8

LinkedHashMap is a subclass of HashMap so you can use it as a HashMap.

Resources :

javadoc - LinkedHashMap

answered Sep 23 '10 at 17:30

Colin Hebert

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I agree. I should not matter what implementation of a HashMap it uses. – sbglasius Sep 23 '10 at 20:00

score 4 · Answer 2 · answered Oct 14 '10 at 02:31

4

Simple answer -- maps have something that looks a lot like a copy constructor:

Map m = ['foo' : 'bar', 'baz' : 'quux'];
HashMap h = new HashMap(m);

So, if you're wedded to the literal notation but you absolutely have to have a different implementation, this will do the job.

But the real question is, why do you care what the underlying implementation is? You shouldn't even care that it's a HashMap. The fact that it implements the Map interface should be sufficient for almost any purpose.

answered Oct 14 '10 at 02:31

conleym

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I came across the same issue, whereby I am trying to compare a Map in an assertEquals via `assertEquals("Checking Data Input Variable 5/9 - Define attr", ["male": 0, "female": 1], var5.define)` and the assertion fails because the actual type is `HashMap` whereas the expected type is `LinkedHashMap`. Maybe I'll write my own `assertMapEquals()` function that uses your suggestion... – Matthew Wise Mar 30 '15 at 12:30

score 2 · Answer 3 · edited Mar 19 '12 at 14:21

He probably got caught with the dreaded Groovy-Map-Gotcha, and was stumbling around in the wilderness of possibilities as I did for the entire afternoon.

Here's the deal:

When using variable string keys, you cannot access a map in property notation format (e.g. map.a.b.c), something unexpected in Groovy where everything is generally concise and wonderful ;--)

The workaround is to wrap variable keys in parens instead of quotes.

def(a,b,c) = ['foo','bar','baz']  
Map m = [(a):[(b):[(c):1]]]  
println m."$a"."$b"."$c" // 1  
println m.foo.bar.baz // also 1

Creating the map like so will bring great enjoyment to sadists worldwide:

Map m = ["$a":["$b":["$c":1]]]

Hope this saves another Groovy-ist from temporary insanity...

score 1 · Answer 4 · answered Sep 23 '10 at 17:30

1

 HashMap h = new HashMap() 
 h.getClass().getName();

works. Using the [:] notation seems to tie it to LinkedHashMap.

answered Sep 23 '10 at 17:30

hvgotcodes

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cast LinkedHashMap to HashMap in groovy

4 Answers4