Question

if i have a type stored in a variable

(def ta java.util.Vector)

how can I initialise a new Vector type with the symbol stored in a?

eg.
(initialize ta params) => #Vector <params>

Answer 1

Well your ta is an instance of java.lang.Class, so you can just use the newInstance method directly:

(.newInstance ta)
=> #<Vector []>

If you want to use parameters to the constructor, you can go via the getConstructor method with something like:

(defn build-constructor [klass & types]
  "Construct a new class instance dynamically at runtime"
  (let [constructor (.getConstructor klass (into-array java.lang.Class types))]
    (fn [& args]
      (.newInstance constructor (object-array args)))))

((build-constructor ta java.util.Collection) [1 2 3 4])
=> #<Vector [1, 2, 3, 4]>

Although this can be a bit more fiddly as you need to exactly match the parameter types in order to obtain the right constructor….