Question

In Clojure how can I read a public member variables of an instance of a Java class? I want something like:

 (. instance publicMemberName)

I also tried:

instance/publicMemberName 

but this only works with static methods

Answer 1

In Java, the class java.awt.Point has public fields x and y. See the javadocs here http://download.oracle.com/javase/6/docs/api/java/awt/Point.html.

In Clojure the dot macro works for fields and methods. This worked for me:

user=> (let [p (new java.awt.Point 2 4)] (.x p))
2

EDIT: The following also works (note the space between the dot and the p):

user=> (let [p (new java.awt.Point 2 4)] (. p x))
2

EDIT: I decided to make a complete example given that java.awt.Point has methods getX and getY in addition to public fields x and y. So here goes. First make a Java class like this:

public class C {
    public int x = 100;
}

Compile it

$ javac C.java

Now move C.class into your clojure directory. Next start the REPL, import the class, and watch it work:

$ java -cp clojure.jar clojure.main
Clojure 1.2.0
user=> (import C)
C
user=> (let [q (new C)] (. q x))
100

Note the other way works too:

user=> (let [q (new C)] (.x q))
100