Develop Reference

Java .class file disappeares as soon as I run the project

I've been on a project where I build tetris that has multiplayer, and it's been working for a couple of days with no problem, but now suddenly there's this exception:
Exception in thread "main" java.lang.NoClassDefFoundError: Game/Piece
This basically means it can't find the .class of my class called Piece, but whenever I do a "clean and build" the .class file appears, then instantly disappears when I run the project.
This is my project structure (running with JDK 16, in netbeans):
Is there a reason for this exception?
My JAVA_HOME variable: jdk1.8.0_131.

While it's possible that this is due to a classpath mismatch between compile-time and run-time, it's not necessarily true.
It is important to keep two or three different exceptions straight in our head in this case:
java.lang.ClassNotFoundException This exception indicates that the class was not found on the classpath. This indicates that we were trying to load the class definition, and the class did not exist on the classpath.
java.lang.NoClassDefFoundError This exception indicates that the JVM looked in its internal class definition data structure for the definition of a class and did not find it. This is different than saying that it could not be loaded from the classpath. Usually this indicates that we previously attempted to load a class from the classpath, but it failed for some reason - now we're trying to use the class again (and thus need to load it, since it failed last time), but we're not even going to try to load it, because we failed loading it earlier (and reasonably suspect that we would fail again). The earlier failure could be a ClassNotFoundException or an ExceptionInInitializerError (indicating a failure in the static initialization block) or any number of other problems. The point is, a NoClassDefFoundError is not necessarily a classpath problem.
And this question has been asked before.

This type of error can appear for multiple reasons :
Because the compiler is too different than the JVM, specially with new Java syntax.
Personally, I had this type of error by running Java 16 code with Java 8 JRE, and I fix it by removing the package with the Java 16 code.
Because you were using deprecated class, which have been removed since this date.
So, to fix your issue, there is multiple ways:
Use same Java in Netbeans and in your project config (to prevent change)
Upgrade your Java JRE installed (instead of old Java 8 version) to have both Java 16
Downgrade Netbeans JDK to Java 8 to have both Java 8
The objective is to use the same JVM than JDK, to see all warns/error that are linked to your current code.

So apperantly I had a warning (not an error) when compiling, it said something was depracated, so I had to add a compiler option name -Xlint:(something here I can't remember), so when I compiled it the issue was obvious, JFrame.hide() is a depracated function so I just had to remove it. It's weird that the runtime error was "NoClassDefFoundError" which has nothing to do with the issue.

Stanford OpenIE example code compile error

http://nlp.stanford.edu/software/openie.shtml generates compile time error :
SemanticGraphCoreAnnotations.EnhancedDependenciesAnnotation cannot be resolved to a type
I am running java-8 under eclipse 2016. corenlp-full-2015-12-01.zip, openie.jar, openie-models.jar are in included in my eclipse project.
Error generated by line of:
System.out.println(sentence.get(SemanticGraphCoreAnnotations.EnhancedDependenciesAnnotation.class).toString(SemanticGraph.OutputFormat.LIST));
thanks

If I were to guess, this sounds like a classpath issue. What happens if you remove either openie.jar or the corenlp distribution? In theory, openie.jar should contain everything you need to run the Open IE system.

I have the same error.
What does this package edu.stanford.nlp.naturalli; in the first line of the code snippet mean?
I do not have much Java knowledge, I just created a Java project somewhere and included the same files as WH Sweet did.
I just found that within the corenlp project subfolder naturalli there is a OpenIEDemo.java already. Maybe the explanation for this would solve the initial problem..

package com.sun.xml.internal.messaging.saaj.soap.dynamic does not exist

I am trying to compile a java file, which uses package com.sun.xml.internal.messaging.saaj.soap.dynamic, using ANT-1.9.3 but I'm receiving error
package com.sun.xml.internal.messaging.saaj.soap.dynamic does not
exist
I tried compiling both JDK7 and JDK 8 and getting the same error.
I can see the package exist inside rt.jar of both JDK. I have set JAVA_HOME also properly.
Can someone help me to resolve this issue?

Unfortunately for you, this behaviour is probably intentional and your usage is deliberately unsupported. If your code used to compile under Java6 and now doesn't under Java7 or Java8 then you've basically fallen foul of
From one release to another, these classes may be removed, or they may be moved from one package to another
http://www.oracle.com/technetwork/java/faq-sun-packages-142232.html
See also http://bugs.java.com/bugdatabase/view_bug.do?bug_id=6778491 for a technical description of a possible cause of not being able to compile a class which references a 'com.sun.*' class but which throws the same compiler error you're seeing despite the fact that the referenced class exists in rt.jar. Also for the kind of response which Oracle give to bug reports relating to it;)
Unfortunately, using undocumented, unsupported APIs often has this kind of 'bite you in the posterior' kind of effect.

Please add the line, < compilerarg line="-XDignore.symbol.file" compiler="modern"/ > for < javac > tag in your build.xml. This should solve your problem. It solved for me.
For reference you can view the forum link
http://www.icesoft.org/JForum/posts/list/19871.page#sthash.srrN9Ijk.dpbs

NoClassDefFoundError when code moved from R2007a to R2013a

I am working on moving code from R2007a to R2013a. I am getting a java.lang.NoClassDefFoundError during my run in R2013a which does not appear in R2007a. It occurs when I call.
feval('get',fname,jevent);
Where fname is a product.ProxyField object for an Object Filter and jevent is a product.format.java.internal.JavaEvent.
The class is in a jar file on the path and is being accessed by another class in the same jar file. The stack trace does not leave the realm of the product if that helps.
I do not have access to the original code for the jar file. I do have access to code derived from that original code and both classes are in the same package. I'm guessing this has something to do with differences in the java version but I'm not sure what to do since I don't have the original code to recompile.
Unfortunately I can't provide actual source or full detail but a google search only yielded results for MATLAB startup issues. Any thoughts?

Seems like the difference between R2007a and R2013a is that the first uses 1.5 jre and second uses 1.6 jre. It would be easier to help you if you provided the stack trace showing the exception. Sometimes classes get moved around in between jvm versions, so having the actual missing classes would help in determining if the missing class is a class that was just moved around to a different package. You could take the missing class, google it adding the same exception message as you put above and seeing who else ran into similar issues.

Why does my servlet stacktrace show "Unknown Source" for my classes?

I'm currently using Apache Tomcat 5.5.16 to serve a Lucene-based search API.
Lately I've been having some NullPointerExceptions inside my servlet class. The class is called com.my_company.search.servlet.SearchServlet.
With certain types of input I can routinely create a NullPointerException, but I'm having trouble figuring out where exactly it is.
The StackTrace indicates that the bug is occuring here:
com.my_company.search.servlet.SearchServlet.doGet(Unknown Source)
The source and .class files for this class is all in:
$TOMCAT_HOME/webapps/my_servlet/WEB-INF/classes/com/my_company/search/servlet/
My question is, how can I get Tomcat to provide me with more descriptive error locations?

Tomcat cannot provide you more detailed information unless the classes in question were compiled with debugging information. Without this debugging information, the JVM cannot determine what line of code the error occurred on.
Edit: You can ask the compiler to include this information by specifying the -g option when running javac on the command line. You can also specify this option using the debug parameter of the Javac Ant task.

you have to add debugging information to your classes. compile them with the option -g:
javac -g YourServlet.java

the location unknown source can occurs when the JIT compiler has optimized your class. At that point the source information is lost. to get the original location, restart the server and retry your test. Most of the time you will get the location in your source