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App.java is not on the classpath of project ss_d36b3017, it will not be compiled to a .class fileJava(32)

I am constantly facing this error and I have no idea how to fix it.
App.java is not on the classpath of project ss_d36b3017, it will not be compiled to a .class fileJava(32)
I am using Visual Studio Code for writing Java. I have set up the environment variable. javac --version and java --version and giving the expected results in PowerShell. I am using a very simple folder convention than is made by VS Code pallet. It has 1 folder (in drive D:)named project which has 3 folder named lib(This is vacant), src(This has the App.java)<readme.md It has no building tools. Code inside the App.java does not affect the issue.
I need some help.

Try the following two ways to see if question goes away.
Open Command Palette and choose Java: Clean Java Language Server Workspace
Right click the folder src and choose Add Folder to Java Source Path, then reload the window.

Using System.loadLibrary on jar library using windows

I am using a Windows 10 OS and try to get JPBC (Pair-Based Cryptographie) running, as explained here: http://gas.dia.unisa.it/projects/jpbc/buildHowto.html#.WVlWQ4jyhhE . The installation worked well for the libraries and now I am having a bunch of folders, including .jar and .java files in my local maven repo .m2\repository\it\unisa\dia\gas. One of the files is jpbc-pbc for instance but there are more
Now I imported a project from gradle that needs some of those files. This projects includes the line
System.loadLibrary("jpbc-pbc");
Now, this throws an error:
Could not load library jpbc-pbc. JCPABE will be extremely slow.
java.lang.UnsatisfiedLinkError: no jpbc-pbc in java.library.path
at java.lang.ClassLoader.loadLibrary(ClassLoader.java:1867)
at java.lang.Runtime.loadLibrary0(Runtime.java:870)
at java.lang.System.loadLibrary(System.java:1122)
at cpabe.Cpabe.<clinit>(Cpabe.java:24)
at cpabe.demo.DemoForCpabe.main(DemoForCpabe.java:63)
My path variable links to C:\Program Files\Java\jdk1.8.0_131 . Now whatever I try, putting the .jar into it or the src folder or both or whatever, I receive this error.
What am I doing wrong?
Folder structure of jpbc-pbc is
jpbc-pbc
/2.0.0
//jpbc-pbc-2.0.0.jar
/src
//main (and so on)
//test (and so on)
/CMakeLists.txt
/FindGMP.cmake
/FindPBC.cmake
/maven-metadata-local.xml
/pom.xml

The jpbc-pbc library is not in your java.library.path.
Try adding it using:
1. Command Line
java -Djava.library.path=<path_to_dll> <main_class>
2. Source Code
System.setProperty(“java.library.path”, “/path/to/library”);
3. IDE
Depends on the IDE you are using, for example in Eclipse you could:
Right-click on your project in the package explorer
Choose Build Path -> Configure Build Path
Add your library in the Libraries Tab

Where is the Java "jar" function

I'm looking to make a jar file out some Java code using jar [options] [name] [files] from the command line but it's not recognized.
According to Oracle Jar is part of the JDK. I have both 7 and 8 installed. How do I run the jar function?
I don't have a C:/Java that the Oracle documents show. I've tried running jar from within the JDK directories and with admin rights.
I'm not putting params in yet, want to check I can at least find the jar function first.
Running jar from JDK directory(1.8) http://puu.sh/eoer7/4fcd0ce63c.png
Running jar from System32 http://puu.sh/eoe3X/076d79b4e4.png

You have displayed two installations of the Java Runtime Environment (or JRE). You need to install a Java Developer Kit (or JDK), to get jar. Set your JAVA_HOME to the installation directory of the JDK, and add it to your PATH.
set "PATH=%PATH%;%JAVA_HOME%\bin"
Also, Using JAR Files: The Basics says (in part) JAR files are packaged with the ZIP file format, and you can use tools that can read and write ZIP files to work with them.

Problem while setting jad with Eclipse Helios

I am using jad to decompile my java class files through Eclipse. I have installed net.sf.jadclipse_3.3.0.jar plugin for Eclipse
I put the jar in the Eclipse plugins directory.
Next I have downloaded the jad windows plugin (jadretro-win32-x86-jcgo) for my Windows 7.
Next I have started Eclipse and provided the path for the jadretro.exe in Eclipse.
But when i am trying to decompile my class files, its showing the error message -:
/jadclipse/
//Error!
Can someone please help ? I am using Eclipse Helios.

i hope you are not trying to view your class files (for which you have the source code). Jad throws the error
/Jadclipse/
//Error!
Pls try to view an OOTB jar or an imported jar

I guess, you should specify the path to jad.exe instead.

Ant error when trying to build file, can't find tools.jar?

When I run ant it says:
Unable to locate tools.jar. Expected to find it in C:\Program Files\Java\jre6\lib\tools.jar
Buildfile: build.xml does not exist!
Build failed
What package can I use to download the file required > C:\Program Files\Java\jre6\lib\tools.jar
I just downloaded this one:
jre-6u19-windows-i586-s.exe
but unfortunately it appears that it was not on it...

Java ships in 2 versions: JRE & SDK (used to be called JDK)
The JRE in addition to not containing the compiler, also doesn't contain all of the libraries available in the JDK (tools.jar is one of them)
When you download Java at: http://java.sun.com/javase/downloads/index.jsp, make sure to select the JDK version and install it. If you have both a JDK & JRE, make sure that ANT is using the JDK, you can check JAVA_HOME (environment variable), and on the commandline if you do "javac -version" you should get a version description.

You need JDK for that.
Set JAVA_HOME to point to the JDK.

Using suggestions from answers on this page and this other one (ANT_HOME is set incorrectly or ant could not be located), the ultimate fix was the following:
Adding a ANT_HOME environment variable that points to the ROOT directory of your Apache ant directory location. (Not the bin sub-dir!)
Adding a JAVA_HOME environment variable that points to the ROOT directory of your Java JDK (or SDK) directory location. (NOT your JRE and not the bin sub-dir!)
Appended %ANT_HOME%\bin;%JAVA_HOME%\bin to the PATH environment variable.
Make sure you close any command window(s) that were open prior to the changes above. Only command windows opened after the changes will have the updated environment variables.

I was having the same problem, none of the posted solutions helped. Finally, I figured out what I was doing wrong. When I installed the Java JDK it asked me for a directiy where I wanted to install. I changed the directory to where I wanted the code to go. It then asked for a directory where it could install the Runtime Environment and I selected the SAME DIRECTORY where I installed the JDK. It over wrote my lib folder and erased the tools.jar. Be sure to use different folders during the install. I used my custom folder for the JDK and the default folder for the RE and everything worked fine.

I found that even though my path is set to JDK, the ant wants the tools.jar from jre folder. So just copy paste the tools.jar folder from JDK to jre.

I was also getting the same problem, but i uninstalled all updates of java and now it is working very fine....

Just set your java_home property with java home (eg:C:\Program Files\Java\jdk1.7.0_25) directory.
Close command prompt and reopen it.
Then error relating to tools.jar will be solved.
For the second one("build.xml not found ") you should have to ensure your command line also at the directory where your build.xml file resides.

Sometimes while installing JDK, you may get a dll is missing error. Because of this, it won't copy the tools.jar file to the java folder. So please reinstall the JDK in a different location and if it is successful then you will see the tools.jar file.