Cast ConcurrentHashMap to ConcurrentHashMap when B implements A

Question

I have an interface called SerializableL that is implemented by 3 different classes:

I started refactoring and wanted to replace multiple paragraphs with multiple method calls.

public void load(ConcurrentHashMap<String, SerializableL> map, 
ArrayList<SerializableForL> preparedList)

I've written the following code and get the following error.

Code:

ConcurrentHashMap<String, SerializableForL> test = DBStore.Cache.get(tag);

Error:

Type mismatch: cannot convert from ConcurrentHashMap<String,Banner> to 
    ConcurrentHashMap<String,SerializableForL>

How can I do a workaround?

I want a way to cast (ConcurrentHashMap<String,Banner> to ConcurrentHashMap<String,SerializableForL>) .

A banner IS a SerializableForL.

The error is correct. The compiler doesn't think that is a safe operation for good reason. If you know it shouldn't be a problem you can use type erasure and cast it to a `(ConcurrentHashMap)` — Peter Lawrey, Feb 13 '14 at 16:39
`ConcurrentHashMap test = (ConcurrentHashMap) DBStore.Cache.get(tag);` — Peter Lawrey, Feb 13 '14 at 16:41

score 4 · Accepted Answer · edited May 23 '17 at 12:23

4

You can't assign a Map<String,Banner> to a Map<String,SerializableForL> even if Banner implements SerializableForL.

However, if you only care about the values being SerializableForL you should be able to write:

ConcurrentMap<String, ? extends SerializableForL> test = DBStore.Cache.get(tag);

edited May 23 '17 at 12:23

Community

answered Feb 13 '14 at 16:40

assylias

1

+1 This is seriously some dark sorcery.... Sometimes problems like these make me want to go be a stripper heh. – Menelaos Feb 13 '14 at 16:53

1 Answers1