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Executing the single code java file using java Vs javac using jdk11

I am using JDK11. Below is my sample class -
public class SayHi {
public static void main(String[] args) {
System.out.println("Hi There");
}
}
I executed the above class with command "java filename.java" for below scenarios
ColumnA -> Class declared as public?
ColumnB -> File name same as class name?
ColumnA ColumnB Result
Yes Yes Yes
No Yes Yes
*Yes No Yes
No No Yes
For all the scenarios, the command executed successfully and I got the result. I get compile-time error for the "Yes-No" case, if I run the "javac" command on the file name.
Why I am not getting the compile-time error when I am executing "java" command on the file name?
I have multiple public classes in a single code file. I am able to execute the file using "java filename.java" command. What I am missing with the compile-time issues when running the file with "java" command. Please help me on this.

The answers to all your questions can be found in JEP 330. I believe the following excerpts provide answers to your questions.
the first class found in the source file is executed
The source file should contain one or more top-level classes, the first of which is taken as the class to be executed
The compiler does not enforce the optional restriction defined at the end of JLS §7.6, that a type in a named package should exist in a file whose name is composed from the type name followed by the .java extension
In other words, when you compile a java source code file with javac, the source code file must contain a single, "public" class whose name matches the name of the file. But when you run a java source code file using the java command, the above restriction does not apply.
The class to be executed is the first top-level class found in the source file. It must contain a declaration of the standard public static void main(String[]) method.

Run single junit test with cli

I need to run a single test case run through the cli. I created a runner class
public class Runner {
public static void main(String ... args) throws ClassNotFoundException {
String[] classAndMethod = args[0].split("#");
Request request = Request.method(Class.forName(classAndMethod[0]),
classAndMethod[1]);
Result result = new JUnitCore().run(request);
System.exit(result.wasSuccessful() ? 0 : 1);
}
}
using this answer
Run single test from a JUnit class using command-line.
I downloaded from github a project (https://github.com/apache/incubator-dubbo) on which I want to run the single method, I positioned myself from terminal on the directory containing the Runner class I created and I launched the following command:
java -cp /path/incubator-dubbo/dubbo-cluster /usr/share/java/junit4-4.12.jar /pathClassRunner/src/com/company/Runner org.apache.dubbo.rpc.cluster.StickyTest#testHeartbeat
but I got the following error:
Error: Could not find or load main class pathClassRunner.src.com.company.Runner
can someone help me?
thanks

The command expects you to include any paths in the classpath with NO spaces. A space means that the arguments for the classpath has ended. It there is a space in one of your paths you may include double quotes:
java -cp path1:path2:path3 classname argument
java -cp "path1:path2:path3" classname argument
If a path starts with / it's a full path. If not it's relative to where you run your command. The classname must be the name of the class, not the file, so that means no .class. If your class specifies any package, then the classname is required to contain the package name too, and the path is to the root of the package, not the class itself.
Check that your user has proper access to the files, then try:
java -cp /path/incubator-dubbo/dubbo-cluster:/usr/share/java/junit4-4.12.jar:/pathClassRunner/src/com/company Runner org.apache.dubbo.rpc.cluster.StickyTest#testHeartbeat
I'm assuming your Runner is in the default package. In case it's in the com.company package, you'll want to run this instead:
java -cp /path/incubator-dubbo/dubbo-cluster:/usr/share/java/junit4-4.12.jar:/pathClassRunner/src com.company.Runner org.apache.dubbo.rpc.cluster.StickyTest#testHeartbeat
Another assumption is that your Runner.class is in your /pathClassRunner/src... directory.

Internal Action was not loaded Error: java.lang.ClassNotFoundException

I am trying to run an implementation a jason code that is using some Internal Actions. The interpreter is showing that it was not possible to find the "java" code of the internal action, as showed:
Server running on http://191.36.8.42:3272
[aslparser] [peleus.asl:29] warning: The internal action class for 'org.soton.peleus.act.plan(Goals)' was not loaded! Error:
java.lang.ClassNotFoundException: org.soton.peleus.act.plan
[aslparser] [peleus.asl:42] warning: The internal action class for 'org.soton.peleus.act.isTrue(H)' was not loaded! Error:
java.lang.ClassNotFoundException: org.soton.peleus.act.isTrue
[peleus] Could not finish intention: intention 1: +des([on(b3,table),on(b2,b3),on(b1,b2)])[source(self)] <- ... org.soton.peleus.act.plan(Goals); !checkGoals(Goals); .print("Goals ",Goals," were satisfied") /
{Goals=[on(b3,table),on(b2,b3),on(b1,b2)]}Trigger: +des([on(b3,table),on(b2,b3),on(b1,b2)])[noenv,code(org.soton.peleus.act.plan([on(b3,table),on(b2,b3),on(b1,b2)])),code_line(29),code_src("peleus.asl"),error(action_failed),error_msg("no environment configured!"),source(self)]
[peleus] Adding belief clear(table)
This mas2j file is as following:
MAS peleus {
infrastructure: Centralised
agents:
peleus;
}
Part of agent code (written by Felipe Meneguzzi) is showed bellow:
//The next line is line 28
+des(Goals) : true
<- org.soton.peleus.act.plan(Goals);
!checkGoals(Goals);
.print("Goals ",Goals," were satisfied").
+!checkGoals([]) : true <- true.
//The next line is line 40
+!checkGoals([H|T]) : true
<- .print("Checking ", H);
org.soton.peleus.act.isTrue(H);
!checkGoals(T).
I guess it is about the folder structure, how to set up Jason to search for java files in specific locations?
The folders structure is like this:
Peleus\src\org\soton\peleus for java files
Peleus\examples for mas2j and asl tested project

It all depends on how you are executing the application.
If you are using java, the CLASSPATH should be defined to include the missing classes.
if you are using jason script (that uses Ant), the .mas2j file should include the class path as well.
More on that in the FAQ. Notice that CLASSPATH is where .class files are found, not .java source code files. The error regards a missing class, not a missing source code.

Error in Udf of pig

I am new to pig. I wrote a UDF in pig and used it in my pig script. But it gives following error
ERROR org.apache.pig.tools.grunt.Grunt - ERROR 1070: Could not resolve UserDefined.PartsOfSpeech using imports: [, java.lang., org.apache.pig.builtin., org.apache.pig.impl.builtin.]
Here is my UDF code
public String exec(Tuple input) throws IOException {
//my code here
}
Here is my pig script
REGISTER /home/bigdata/NetBeansProjects/UserDefined/dist/UserDefined.jar
a = load '/user/bigdata/json' using TextLoader() as (input:chararray);
b = foreach a GENERATE UserDefined.PartsOfSpeech(input);
In the above code UserDefined is my package name and PartsOfSpeech is my class name

The error message says that Pig cannot find UserDefined.PartsOfSpeech.
What package declaration does PartsOfSpeech.java have at the top of the file?
If the package declaration is package com.my.company; try this instead:
REGISTER /home/bigdata/NetBeansProjects/UserDefined/dist/UserDefined.jar
a = load '/user/bigdata/json' using TextLoader() as (input:chararray);
b = foreach a GENERATE com.my.company.PartsOfSpeech(input);
That is, replace UserDefined.PartsOfSpeech(input) with com.my.company.PartsOfSpeech(input) since the UDF is located in the package com.my.company.
Also, consider using the DEFINE keyword in your Pig script so you don't need to repeat com.my.company every time you use PartsOfSpeech.
DEFINE PartsOfSpeech UserDefined.dist.PartsOfSpeech();
REGISTER /home/bigdata/NetBeansProjects/UserDefined/dist/UserDefined.jar
a = load '/user/bigdata/json' using TextLoader() as (input:chararray);
b = foreach a GENERATE PartsOfSpeech(input);
There is more information about DEFINE in Chapter 5 of Alan Gates' Programming Pig: http://chimera.labs.oreilly.com/books/1234000001811/ch05.html#udf_define.
Here is an example of DEFINE from Gates' book:
--define.pig
register 'your_path_to_piggybank/piggybank.jar';
define reverse org.apache.pig.piggybank.evaluation.string.Reverse();
divs = load 'NYSE_dividends' as (exchange:chararray, symbol:chararray,
date:chararray, dividends:float);
backwards = foreach divs generate reverse(symbol);

Before compiling your UDF(java class) make sure you have mentioned package name properly. for example if you have mentioned package name-
package com.pig.udf;
It means you need to take care of directory in your linux box as well.
you can follow below mentioned steps to create jar -
Create directory using
mkdir -p com/pig/udf
Create your java class with package com.pig.udf
Compile your java source code using command
javac -cp /usr/lib/pig-0.12.0.2.0.6.0-76.jar YourClass.java
Then go to the directory where you want to create jar for now -
cd ../../..
Now create jar using below command
jar -cvf yourJarName.jar com/
Register the jar in your script using keyword "register" followed by path of the jar
Now use your jar with keyword com.pig.udf.YourJavaClassName
for your scenerio -
REGISTER /home/bigdata/NetBeansProjects/UserDefined/dist/UserDefined.jar
a = load '/user/bigdata/json' using TextLoader() as (input:chararray);
b = foreach a GENERATE com.pig.udf.PartsOfSpeech(input);

class file for javax.serverlet.GenericServlet not found

I have stuck in the class->header file for couple days!
I have tried on jni on Client by http://netbeans.org/kb/docs/cnd/beginning-jni-linux.html and http://ringlord.com/jni-howto.html. And it succeeded in return "hello JNI C++" from JNI's (.cpp)file. Here are my steps:
create native function and in client.java
clean &build this client.java on Netbeans IDE, then result a client.class file
javah –jni [package].[classname]
create a dynamic library C++ project as first reference does, and put client.h into source file, and put some hello code into (.cpp)file ---> It works!
However, I tried to do the same thing on the servlet side and it's not working
Servlet.java->Servlet.class : ok!
Servlet.class->Servlet.h: fail!!!!
Error : cannot access javax.servlet.GenericServlet
class file for javax.servlet.GenericServlet not found
The following are solutions I have found and tried so far,
check the package name
sudo gedit /etc/profile,sudo gedit .bashrc, sudo /etc/environment; add JAVA_HOME & CLASSPATH on them, and source them to update, then echo $JAVA_HOME, echo $CLASSPATH to verify
download servlet-api-6.0.14.jar & servlet-api-5.0.16.jar from http://www.jarfinder.com/index.php/java/info/javax.servlet.GenericServlet
,and add above two (.jar) by netbeans IDE->server->property->libraries->Add JAR
Please tell me how to figure it out this issue, thank you very much!!Btw, I am using hessianServlet

NativeWrapper.java (you run javah only on this class)
class NativeWrapper {
// either
static {
System.loadLibrary("MyOpenCVNative");
}
// or
public NativeWrapper() {
System.loadLibrary("MyOpenCVNative");
}
public native void callNative();
}
MyServlet.java
class MyServlet extends javax.servlet.GenericServlet {
private NativeWrapper nativeWrapper = new NativeWrapper();
public void someServletMethod() {
nativeWrapper.callNative();
}
}