Eclipse - JAR creation failed "Class files on classpath not found or not accessible for..."

Question

I have a project in Eclipse that has a red cross on it and will not export to a runnable JAR. I can't remember if I have looked at it since I reinstalled Windows on my laptop, but I know that I haven't changed any code. There are no errors in any of the classes, however the error I get points to the following class that deals with the menu items on Mac OSx:

import java.lang.reflect.*;

public class osxhandler implements InvocationHandler {

    protected Object targetObject;
    protected Method targetMethod;
    protected String proxySignature;

    static Object macOSXApplication;

    // Pass this method an Object and Method equipped to perform application shutdown logic
    // The method passed should return a boolean stating whether or not the quit should occur
    public static void setQuitHandler(Object target, Method quitHandler) {
        setHandler(new HOsx("handleQuit", target, quitHandler));
    }


    public static void setAboutHandler(Object target, Method aboutHandler) {
        boolean enableAboutMenu = (target != null && aboutHandler != null);
        if (enableAboutMenu) {
            setHandler(new HOsx("handleAbout", target, aboutHandler));
        }
        // If we're setting a handler, enable the About menu item by calling
        // com.apple.eawt.Application reflectively
        try {
            Method enableAboutMethod = macOSXApplication.getClass().getDeclaredMethod("setEnabledAboutMenu", new Class[] { boolean.class });
            enableAboutMethod.invoke(macOSXApplication, new Object[] { Boolean.valueOf(enableAboutMenu) });
        } catch (Exception ex) {
            System.err.println("MacOSHandler could not access the About Menu");
            ex.printStackTrace();
        }
    }

       public static void setPreferencesHandler(Object target, Method prefsHandler) {
            boolean enablePrefsMenu = (target != null && prefsHandler != null);
            if (enablePrefsMenu) {
                setHandler(new HOsx("handlePreferences", target, prefsHandler));
            }
            // If we're setting a handler, enable the Preferences menu item by calling
            // com.apple.eawt.Application reflectively
            try {
                Method enablePrefsMethod = macOSXApplication.getClass().getDeclaredMethod("setEnabledPreferencesMenu", new Class[] { boolean.class });
                enablePrefsMethod.invoke(macOSXApplication, new Object[] { Boolean.valueOf(enablePrefsMenu) });
            } catch (Exception ex) {
                System.err.println("MacOSHandler could not access the About Menu");
                ex.printStackTrace();
            }
        }

        // Pass this method an Object and a Method equipped to handle document events from the Finder
        // Documents are registered with the Finder via the CFBundleDocumentTypes dictionary in the 
        // application bundle's Info.plist
        public static void setFileHandler(Object target, Method fileHandler) {
            setHandler(new HOsx("handleOpenFile", target, fileHandler) {
                // Override MacOSHandler.callTarget to send information on the
                // file to be opened
                public boolean callTarget(Object appleEvent) {
                    if (appleEvent != null) {
                        try {
                            Method getFilenameMethod = appleEvent.getClass().getDeclaredMethod("getFilename", (Class[])null);
                            String filename = (String) getFilenameMethod.invoke(appleEvent, (Object[])null);
                            this.targetMethod.invoke(this.targetObject, new Object[] { filename });
                        } catch (Exception ex) {

                        }
                    }
                    return true;
                }
            });
        }

        // setHandler creates a Proxy object from the passed MacOSHandler and adds it as an ApplicationListener
        @SuppressWarnings({ "unchecked", "rawtypes" })
        public static void setHandler(HOsx adapter) {
            try {
                Class applicationClass = Class.forName("com.apple.eawt.Application");
                if (macOSXApplication == null) {
                    macOSXApplication = applicationClass.getConstructor((Class[])null).newInstance((Object[])null);
                }
                Class applicationListenerClass = Class.forName("com.apple.eawt.ApplicationListener");
                Method addListenerMethod = applicationClass.getDeclaredMethod("addApplicationListener", new Class[] { applicationListenerClass });
                // Create a proxy object around this handler that can be reflectively added as an Apple ApplicationListener
                Object MacOSHandlerProxy = Proxy.newProxyInstance(HOsx.class.getClassLoader(), new Class[] { applicationListenerClass }, adapter);
                addListenerMethod.invoke(macOSXApplication, new Object[] { MacOSHandlerProxy });
            } catch (ClassNotFoundException cnfe) {
                System.err.println("This version of Mac OS X does not support the Apple EAWT.  ApplicationEvent handling has been disabled (" + cnfe + ")");
            } catch (Exception ex) {  // Likely a NoSuchMethodException or an IllegalAccessException loading/invoking eawt.Application methods
                System.err.println("Mac OS X Adapter could not talk to EAWT:");
                ex.printStackTrace();
            }
        }

        // Each MacOSHandler has the name of the EAWT method it intends to listen for (handleAbout, for example),
        // the Object that will ultimately perform the task, and the Method to be called on that Object
        protected HOsx(String proxySignature, Object target, Method handler) {
            this.proxySignature = proxySignature;
            this.targetObject = target;
            this.targetMethod = handler;
        }

        // Override this method to perform any operations on the event 
        // that comes with the various callbacks
        // See setFileHandler above for an example
        public boolean callTarget(Object appleEvent) throws InvocationTargetException, IllegalAccessException {
            Object result = targetMethod.invoke(targetObject, (Object[])null);
            if (result == null) {
                return true;
            }
            return Boolean.valueOf(result.toString()).booleanValue();
        }

        // InvocationHandler implementation
        // This is the entry point for our proxy object; it is called every time an ApplicationListener method is invoked
        public Object invoke (Object proxy, Method method, Object[] args) throws Throwable {
            if (isCorrectMethod(method, args)) {
                boolean handled = callTarget(args[0]);
                setApplicationEventHandled(args[0], handled);
            }
            // All of the ApplicationListener methods are void; return null regardless of what happens
            return null;
        }

        // Compare the method that was called to the intended method when the MacOSHandler instance was created
        // (e.g. handleAbout, handleQuit, handleOpenFile, etc.)
        protected boolean isCorrectMethod(Method method, Object[] args) {
            return (targetMethod != null && proxySignature.equals(method.getName()) && args.length == 1);
        }

        // It is important to mark the ApplicationEvent as handled and cancel the default behavior
        // This method checks for a boolean result from the proxy method and sets the event accordingly
        protected void setApplicationEventHandled(Object event, boolean handled) {
            if (event != null) {
                try {
                    Method setHandledMethod = event.getClass().getDeclaredMethod("setHandled", new Class[] { boolean.class });
                    // If the target method returns a boolean, use that as a hint
                    setHandledMethod.invoke(event, new Object[] { Boolean.valueOf(handled) });
                } catch (Exception ex) {
                    System.err.println("MacOSHandler was unable to handle an ApplicationEvent: " + event);
                    ex.printStackTrace();
                }
            }
        }    
}

Any ideas as to why I can't export/compile? I've never had this issue before.

Answer 1

Just do a clean and/or rebuild on the project.

You can find it under the Project menu of Eclipse.

Answer 2

I also had a different, degenerate case of this problem. Turned out, we had a class in our project that had a file (so Eclipse kept it on the classpath) but no actual class defined in the file (the file only had imports and a class comment... probably a merge gone wrong). Anyway, deleting the file solved the issue.

Answer 3

It’s quite hateful that Eclipse always generates hidden files .project and .classpath in project folder. Sometimes you’re not aware if something goes wrong in these files.

After upgrading your Eclipse and if you found the following compile error, I’d suggest you to check .classpath in your project folder.

The project was not built since its build path is incomplete. Cannot find the class file for java.lang.Object. Fix the build path then try building this project

Most likely you would see a line like this.

<classpathentry kind="con" path="org.eclipse.jdt.launching.JRE_CONTAINER/    org.eclipse.jdt.internal.debug.ui.launcher.StandardVMType/j2re1.4.2_03"/>

The stupid Eclipse appended this for no reason. Just simply remove it to make it work again. ;)

/org.eclipse.jdt.internal.debug.ui.launcher.StandardVMType/j2re1.4.2_xx

Source: http://hochit.com/2006/07/06/eclipse-upgrading-problem-javalangobject-not-found/

In addition, you can check your project settings in eclipse. Right click on your project and choose properties. Go to Java Build Path and there should be more specific information of the problem. Most likely you set the JDK to an Version which doesn't exist on the new System.

If this doesn't help too, select your project and then use the menu entry Source->Clean Up.

Answer 4

In my case, the classes were empty, and the compiler whined:

Class files on classpath not found or not accessible for: 'ibDemo/src/com/ib/controller/LocationCode.java'
Class files on classpath not found or not accessible for: 'ibDemo/src/com/ib/controller/PairPanel.java'

To solve this I'd to add a class declaration:

public class LocationCode
{

}

and

public class PairPanel
{

}