How do you know which class is being created in DI

[John Strzempa]

I'm from a C# background so new to jira and java. I'm creating a custom field and I see some classes being injected into this method like Issue issue. Looking at the API docs, I see this is an interface so I'm wondering how do I know which class is being created for each interface. I'm assuming it's configured somewhere but not sure where

public Map<String, Object> getVelocityParameters(final Issue issue,
                                                     final CustomField field,
                                                     final FieldLayoutItem fieldLayoutItem)