Clojure: Call Java Method

Create Java Object

(new classname arg1 arg2 …)

Return a Java object of class classname, with its args feed to its constructor. 〔see Java Tutorial: Constructor〕

;; creating Java string object from Clojure
(new String)

;; creating Java java.util.Date object from Clojure
(new java.util.Date)

clojure.core/new

Another way to create a object is by this syntax:

(class_name. arg1 arg2 …)

Note the period immediately following the class name.

example:

;; creating Java string object from Clojure
(new String) ; ⇒ ""

;; equivalent to
(String.)

;; creating Java java.util.Date object from Clojure
(new java.util.Date) ; #inst "2014-11-19T21:06:03.072-00:00"

;; equivalent to
(java.util.Date.)

Call Java Instance Method/Field

To call a Java instance method, use this syntax:

(. object_name method_name args)

is Java's object_name.method_name(args)

It is also equivalent to:

(.method_name object_name args)

example:

;; 2 ways to call Java's string method named codePointAt

(.codePointAt "abc" 0)                  ; 97

(. "abc" codePointAt  0)                 ; 97

;; the unicode codepoint for character a is 97

Call Java Static Method/Field

To call a static method, or get value of a static field, you can use the syntax:

(class_name/method_name args)

example:

;; call Java static method named floor in class Math
(Math/floor 1.7) ; ⇒ 1.0

〔see Java: static〕

Set Java Instance Field

(set! var-symbol expr)

(set! (. instance-expr instanceFieldName-symbol) expr)

(set! (. Classname-symbol staticFieldName-symbol) expr)

Used to set thread-local-bound vars, Java object instance fields, and Java class static fields.

clojure.core/set!

Java Basics

For review of Java Basics, see:

• Java Tutorial
• Java: static
• Java Tutorial: Constructor

Reference

http://clojure.org/reference/java_interop