访问Java类的静态字段时出现问题

Question

I am having an inexplicably hard time doing something that I thought was simplicity itself. I have a JAR file on my classpath. I'm in Emacs, using a SLIME REPL, and I'm trying to access a static field of an instance of a Java class (one inside the JAR).

Here's my class:

public class MainFrame extends JFrame implements WindowListener,
        TreeSelectionListener {
    JPanel panel;
    InfocardWindow infoWindow;
    InfocardBuilder infocardBuilder;
    Main infomlFile;
    static NotecardModel setupModel;
    ...

When I tried:

infwb.cardmaker> (import 'javax.swing.JFrame)
javax.swing.JFrame
infwb.cardmaker> (import 'org.infoml.infocardOrganizer.MainFrame)
org.infoml.infocardOrganizer.MainFrame
infwb.cardmaker> MainFrame/setupModel
; Evaluation aborted.

The error message was:

Unable to find static field: setupModel in class org.infoml.infocardOrganizer.MainFrame
  [Thrown class java.lang.Exception]

I tried switching to a simpler problem: accessing a non-static field. I did it inside a let , to eliminate the possibility that doing this from the REPL might be the source of the problem:

infwb.cardmaker> (let [mainFr (MainFrame.)]
  (println (.panel mainFr)))
; Evaluation aborted.

The error message was:

No matching field found: panel for class org.infoml.infocardOrganizer.MainFrame
  [Thrown class java.lang.IllegalArgumentException]

I got the same result when substituting (.panel mainFr) and (println (. mainFr panel) in the body of the let . Also, no change when switching the REPL to namespace user . (Granted, these are shake-a-dead-chicken voodoo desperation moves.)

Google queries like 'emacs slime clojure unable to access Java class field error "Unable to find static field"' yield nothing useful--most have to do with trying to call Java class methods (not access Java class fields).

Just to be thorough, I tried:

user> (let [mainFr (MainFrame.)]
  MainFrame/setupModel)
; Evaluation aborted.

The error message was, as before:

Unable to find static field: setupModel in class org.infoml.infocardOrganizer.MainFrame
  [Thrown class java.lang.Exception]

Bottom line: Given an instance of MainFrame, what do I need to do to access either a static or non-static field? Thanks for any help or hints you can provide.

Answer 1

Read the Controlling Access to Members of a Class tutorial. You'll find that you need to either use the public modifier, or be aware that since there is no modifier (the default, also known as package-private), it is visible only within its own package.

Answer 2

public class MainFrame extends JFrame implements WindowListener,
50                  TreeSelectionListener {
51          JPanel panel;
52          InfocardWindow infoWindow;
53          InfocardBuilder infocardBuilder;
54          Main infomlFile;
55          static NotecardModel setupModel;
            ...
}

The field is not publicly accessible. Read the source . You need to use the public modifier.