How to use multiple wildcards in an API call

Question

I'm working with Anthill (an UrbanCode/IBM product) and one of the methods requires a parameter of type java.lang.Class<? extends SourceConfig<?>> sourceConfigType.

After reading the tutorial on generics I found that a class GitSourceConfig is a subclass of SourceConfig but I don't understand how the generic of SourceConfig<?> works in this context. Any ideas?

The end goal is to get a GitSourceConfig object and call the getRepositoryUrl/setRepositoryUrl methods. The Anthill Pro API is here and I'm looking at the SourceConfig class.

score 0 · Answer 1 · answered Jul 29 '14 at 16:56

0

The generic bounded wildcard type in your example java.lang.Class<? extends SourceConfig<?>> sourceConfigType specifies that sourceConfigType is any class that can be bound by the upper bound type of SourceConfig.

From the tutorial,

List<? extends Shape> is an example of a bounded wildcard. The ? stands for an unknown type, just like the wildcards we saw earlier. However, in this case, we know that this unknown type is in fact a subtype of Shape. (Note: It could be Shape itself, or some subclass; it need not literally extend Shape.)

Note SourceConfig itself is also generic, and here it is using a regular unbounded wildcard.

answered Jul 29 '14 at 16:56

Elliott Frisch

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I think OP's confusion stems from the fact that `SourceConfig` itself is generic, and has a wildcard too. – Thorn G Jul 29 '14 at 16:57
@TomG Exactly. How do you work with that? I understand `GitSourceConfig extends SourceConfig` but I don't understand how the second generic works. – Wheeler Jul 29 '14 at 17:00
@Wheeler See (unbounded) wildcards in the link in my answer. – Elliott Frisch Jul 29 '14 at 17:01

score 0 · Answer 2 · answered Jul 29 '14 at 17:04

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Class is generic -- if you invoke getClass() on a String object result will be of type Class<String>.

In this case SourceConfig<R extends Repository> itself a generic so you have nested generics.

if you check definition of GitSourceConfig

public class GitSourceConfig extends SourceConfig<GitRepository>

and

public class GitRepository extends Repository

so Class<GitSourceConfig> matches Class<? extends SourceConfig<?>>

answered Jul 29 '14 at 17:04

mzzzzb

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After a little research, it looks like I'd use this as: `Class GitSourceConfigClass = (Class) p.getSourceConfigType();` `GitSourceConfig gsc = GitSourceConfigClass.newInstance();` This will give me the default constructor for a `GitSourceConfig` object. My source is the second answer on **[this question](http://stackoverflow.com/questions/4453349/what-is-class-objectjava-lang-class-in-java)**. – Wheeler Jul 29 '14 at 17:50

How to use multiple wildcards in an API call

2 Answers2