1.00 S08 FAQ & Troubleshooting Guide

Applies to: J2SE JDK 5.0 & 6.0, Eclipse 3.2.1 or higher

Last Updated: 2/13/2008

Can’t find a question/solution? E-mail your problem to davidcw[at]mit[dot]edu.

GENERAL

1. What is the difference between Java 1.6 and 6.0?

Functionally, the two version numbers refer to the exact same release. Java uses two version numbering systems. 1.6 is developer number while 6.0 is the product number. In actuality, the full developer number is 1.6.0, where the trailing “0” is the update number. The leading 1 is dropped to come up with the product number.

2. Why are the due times for the Problem Sets off?

Problem Sets are officially due at noon. We understand that MIT students are busy and that sometimes computer troubles may prevent timely submission. We have setup Stellar to automatically give one hour (until 12:59pm) of leniency for problem set submissions. There is no additional leniency: homework turned in at 1:00 pm is late.

3. Can I run Eclipse on Athena?

Eclipse is known to successfully run on all Sun, IBM, and Dell Athena machines. At an athena shell (prompt):

· Add the “eclipse-sdk” locker:

athena% add eclipse-sdk

· Run eclipse (Do NOT put an “&” after this command!):

athena% eclipse

· Wait. A prompt will appear asking if you wish to accept the default workspace. Hit ENTER.

· A prompt may appear asking to remove/replace a file called “.metadata”. Hit ENTER

· Wait for 1-5 minutes depending on network traffic and you will see Eclipse’s splash. 

4. How to set your Eclipse compiler compliance.

Check to see which version of Java Eclipse is using:

a. Click “Window” on the menu bar. In the drop down menu select “Preferences…”.

b. In the “Preferences” window, expand “Java” in the tree.

c. Click “Installed JREs”

d. In the “Installed JREs” pane, remember the “Name” of the JRE/JDK with a green check mark.

Set the Eclipse compiler compliance.

e. With the “Preferences” window still open, click make sure “Java” is expanded.

f. Click on “Compiler”.

g. In the “Compiler” pane set the Compiler compliance level to a number appropriate for the JRE/JDK Eclipse is using. Remember that version 1.X is the same as version X.0.

h. Click OK. If a window appears prompting you to “rebuild” choose OK.

5. I forgot to put my name on the files in my problem set submission!

If it is BEFORE 1pm on the due date, resubmit and delete your previous submission (if you are close to the 1pm deadline, you may want to resubmit THEN delete just to make sure we have one set of files ‘on-time’). If it is AFTER the deadline, please “add submission”. Instead of selecting a file, type your name, e-mail, TA’s name, & section number in the text entry box.

6. The files in my project are located in a “src” directory. There is also a folder called “bin”…?

We do not recommend this file structure for 1.00.

The “src” and “bin” directories are organizational: the “src” directory is intended to hold .java files (the code) while the “bin” directory holds .class files (the ‘runnable’ files). To keep things simple, we usually recommend the “project” setup, where both .java and .class files are stored in the same directory, directly in your project folder. How do you make this change?

With Eclipse running:

· Choose Window -> Preferences from the Eclipse toolbar.

· In the "Preferences" window, in the navigation tree, expand the "Java" option and click the “Build Path” option.

· In the "Build Path" panel, select the “Project” radio button.

· Click OK to save your changes.

7. 100Zip v1.3 reports “zip failed” when attempting to create a ZIP or SUBMISSION ZIP.

If you are on a Windows Vista machine, 100Zip has compatibility problems with Vista’s User Account Control (UAC) security feature. You may either use another compression utility (WinZip, WinRar, 7Zip) or deactivate UAC and try 100Zip again.

To deactivate UAC:

· Go to the Control Panel -> User Accounts

· Click on the “Turn User Account Control on or off” link.

· Uncheck the checkbox next to “Use User Account (UAC) to help protect your computer”.

· Click OK.

· You may need to restart for the changes to take effect.

8. How to get line numbers in your Eclipse editor.

With Eclipse running:

· Choose Window -> Preferences from the Eclipse toolbar.

· In the "Preferences" window, in the navigation tree, expand the "General" option, expand “Editors”, and click “Text Editors”.

· In the "Text Editors " panel, check the box next to “Show line numbers”.

· Click OK to save your changes.

TROUBLESHOOTING

1. An error message appears intermittently after running or debugging a Java application:

ERROR: JDWP Unable to get JNI 1.2 environment, jvm->GetEnv() return code = -2

JDWP exit error AGENT_ERROR_NO_JNI_ENV(183):  [../../../src/share/back/util.c:820]

This error is believed to be a bug in the implementation of Java 6.0 for Windows. It appears after a program has run to completion and is believed to have no negative side effects. See Bug Report 6476706 for updates:

http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6476706

2. When attempting to debug a Java application you get:

FATAL ERROR in native method: JDWP No transports initialized, jvmtiError=AGENT_ERROR_TRANSPORT_INIT(197)

ERROR: transport error 202: connect failed: Software caused connection abort

ERROR: JDWP Transport dt_socket failed to initialize, TRANSPORT_INIT(510)

JDWP exit error AGENT_ERROR_TRANSPORT_INIT(197): No transports initialized [../../../src/share/back/debugInit.c:690]

The Eclipse debugger supports both local and remote debugging. The debugger requires access to a port. You can avoid this problem in some firewalls/virus scans, by adding “javaw.exe” as an allowable process/application. We are working on a more concise solution.

3. When attempting to run a Java application you get a window that says “Could not find the main class. Program will exit” and errors:

java.lang.UnsupportedClassVersionError: Bad version number in .class file

at java.lang.ClassLoader.defineClass1(Native Method)

at java.lang.ClassLoader.defineClass(ClassLoader.java:620)

…

This is most likely the result of a mismatch between the Eclipse compiler compliance level and J2SE version. See “How to set your Eclipse compiler compliance” to select an appropriate compiler compliance.

4. When I select Run -> Debug As, I see “1 Eclipse Application” and “2 Equinox Framework” instead of “Java Application.”

Make sure you the current active selection (the last thing you clicked) is either:

a. A window pane with a “main()” method.

b. A “XXX.java” file with a “main()” method in the Package Explorer view.

5. I accidentally closed XXX view and now I can’t get it to appear or I can’t get it to look like before I closed it.

All the Eclipse windows/views are available from the “Window” menu item under “Open Perspective” or “Show View”. Once you have selected the View you wish to have, it may not ‘dock’ with Eclipse. In order to get a new view to ‘dock,’ try clicking and dragging its top bar to the edge of Eclipse’s work area. This should allow the View to automatically ‘push’ the other Views aside.

6. The Debugger doesn’t open when I choose Debug As-> Java Application? How do I open the debugger perspective?

The Debug perspective will not automatically open. You can open the debug perspective manually:

1. Click “Window” on the menu bar. In the drop down menu select “Open Perspective”->”Debug.”
2. Or, in the upper right hand corner of Eclipse there is a small blue/white window icon with a yellow plus sign. Click on this icon for another way to open the debug perspective.

Once the Debug perspective is open you should see a “Debug” icon next to the “Java” icon. You can then use these buttons to switch back and forth between the perspectives.

7. I can see my program fine in Eclipse, but when I try to Debug it, the Debugger perspective has a window that claims it “cannot find source”.

The debugger is picky about where you keep your Java source files. Try moving your entire “workspace” folder to the default location. For Windows: “C:/Documents and Settings/USERNAME/workspace”.

8. (MACs) When attempting to debug a Java application you get:

2007-02-15 22:25:11.791 java[2587] CFLog (0): CFMessagePort: bootstrap_register(): failed 1103 (0x44f), port = 0xf503, name = 'java.ServiceProvider'

See /usr/include/servers/bootstrap_defs.h for the error codes.

2007-02-15 22:25:11.792 java[2587] CFLog (99): CFMessagePortCreateLocal(): failed to name Mach port (java.ServiceProvider)

This message is believed to be harmless. Reproduced from: http://lists.apple.com/archives/Java-dev/2005/Jun/msg00546.html

“The message is a system diagnostic telling you that more than one process tried to register Services (i.e. the ‘Services’ submenu of your Application menu) with the process name ‘java’.”- Karl Hsu

9. There are “glitches” in the Preferences window: I can see the navigation tree, but not the panels.

There appears to be a compatibility issue between Eclipse and the Logitech SetPoint drivers (for Logitech brand keyboard and mice). This problem has been reported for 64 bit Windows Vista, but may occur in other operating systems.

Recommendation: Uninstall SetPoint. The SetPoint drivers and utility program adds functionality to Logitech brand devices. Uninstalling SetPoint will most likely fix the problem, but may also disable the functionality of convenience keys (i.e. the media player shortcut key may no longer work).

Second Option: You can “trick” some of the Preferences window panels into appearing by:

· In the navigation tree of the Preferences window, select another panel other than the one you want to see.

· Click OK to exit the Preferences window.

· Re-open the Preferences window (Window->Preferences)

· In the navigation tree, select the option/panel you originally wanted to view.