Clojure Koans 20 Interop Notebook

{:hello (clojure-version)}

;; "You may have done more with Java than you know"

(= java.lang.String (class "warfare")) ; hint: try typing (javadoc "warfare") in the REPL

;; question 20001: Do Clojure strings have any differences from Java strings, and if yes, what are they?

;; skill 20001: Find out the class of a thing in Clojure by using the `class` function

;; skill 20002: Find out more information about a thing (and its underlying implementation?) in Clojure by using the `javadoc` function

;; "The dot signifies easy and direct Java interoperation"

(= "SELECT * FROM" (.toUpperCase "select * from"))

;; skill 20003: Use a native Java function via Java interop

;; "But instance method calls are very different from normal functions"

(= ["SELECT" "FROM" "WHERE"] (map clojure.string/upper-case ["select" "from" "where"]))

;; question 20002: Why can the `map` function only take Clojure functions (not Java interop) ? For example, passing a Java interop for the `toUpperCase()` function to the `map` function results in the following error: "Unable to resolve symbol: .toUpperCase in this context"

;; "Constructing might be harder than breaking"

(= 10 (let [latch (java.util.concurrent.CountDownLatch. 10)]

         (.getCount latch)))

;; question 20003: What exactly is happening here???

;; question 20004: What relevant/pertinent Clojure skill are here to take away?

;; "Static methods are slashing prices!"

(== (reduce * (repeat 10 2)) (Math/pow 2 10))

;; question 20005: Does the Math library in Clojure come from Java?

;; question 20006: How can one determine programmatically where libraries come from? See 20005

;; question 20007: What is the significance of static methods in Clojure?