In some situations you need convert some data structures of clojure (like vectors, maps or sets) to java collections and vice versa.
This problem has simple solution: clojure data structures implements java.util.Collection interface and uses it constructor for make conversion to corresponding types.
As first example, you can convert clojure vector to java.util.ArrayList:
(def list1 (java.util.ArrayList. [1 2 3]))
;; list1 -> #<ArrayList [1, 2, 3]>
(.get list1 0)
;; -> 1
In same way, you can convert clojure map to java.util.HashMap:
(def map1 (java.util.HashMap. {"a" 1 "b" 2}))
;; map1 -> #<HashMap {b=2, a=1}>
(.get map1 "a")
;; -> 1
For backward conver from java to clojure data, you can use into function:
(into [] (java.util.ArrayList. [1 2 3]))
;; -> [1 2 3]
(into #{} (java.util.HashSet. #{1 2 3}))
;; -> #{1 2 3}
(into '() (java.util.LinkedList. '(1 2 3)))
;; -> (3 2 1)
(into {} (java.util.HashMap. {:a 1 :b 2}))
;; ->{:b 2, :a 1}
In clonclusion, clojure has well interoperability with java, and convert form clojure data structures to java collections is almost transparent.