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Could not find or load main class in a simple java project

I have created a simple java project "DesignPatterns".
I created a file FacadePattern.java with the path being ~/DesignPatterns/Structural/FacadePattern/FacadePattern.java
My FacadePattern.java class,
public class FacadePattern {
public static void main(String args[]) {
// Some code
}
}
But my editor (VSCode) gives me an error at the start of the file:
The declared package "" does not match the expected package "Structural.DecoratorPattern"
So upon clicking on quick fix, it added package Structural.FacadePattern; in the first line.
So the final code became
package Structural.FacadePattern;
public class FacadePattern {
public static void main(String args[]) {
// Some code
}
}
But when I compile the above file using the command
javac FacadePattern.java && java FacadePattern
It is giving me the following error:
Error: Could not find or load main class FacadePattern
Caused by: java.lang.NoClassDefFoundError: Structural/FacadePattern/FacadePattern (wrong name: FacadePattern)
After searching a lot in the internet, I ran the following command:
javac -sourcefile ~/DesignPatterns FacadePattern.java && java FacadePattern
But no use, I am getting the same error.
Can anyone explain why my editor gave an error but code ran successfully before? and why wont it compile after adding "package Structural.FacadePattern;" line? and what is -sourcefile parameter in javac command? and how to run the code with successfully without errors in editor as well as the terminal?

Stick to naming rules. Package names should be lowercase only. In your case, it should be package structural.facadepattern;
Run the 'correct' class. Because your class is not inside 'the base folder' aka the 'default package', you have to prefix the class with its package name: java Structural.FacadePattern.FacadePattern or rather java structural.facadepattern.FacadePattern if you use the proper case for packages.

How do I compile my main Java program on the command line when it includes an external java package?

I'm a relative Java newbie so apologies if the question appears somewhat basic. I've googled high and low for an answer here and I'm not finding anything that's helping.
Problem:
Whilst I'm able to integrate external packages into my Java programs from an IDE environment, I am trying to do run a very basic program from the command line that calls on a separate, basic package file that I have written - and am simply doing all this as I want to have a bottom-up understanding of how package files are related to a main program by Java.
I have a program that sits on my desktop named MyProgram.java:
import org.somepackage;
public class MyProgram {
public static void main(String arguments[]) {
System.out.println("Programme up and running...");
Human myHuman = new Human();
myHuman.scream();
}
Still on the Desktop, I then have another folder which I've named src, inside of which I have created the necessary subfolders corresponding to the package name, i.e. ./src/org/somepackage - and in this location, I have the Human.java file which defines the Human class with the following contents:
package org.somepackage;
public class Human {
public void scream() {
System.out.println("I exist!!");
}
}
I then created a classes folder, again on the Desktop, and ran the following compile command on the command line:
javac -d ./classes/ ./src/org/packagename/Human.java
This ran fine and created - as expected - the Human.class file within the ./classes/org/packagename/ location.
However, where I fall down is when I then try to compile MyProgram.java on the command line, i.e.
javac -cp ".:./classes/" MyProgram.java
As you'll see, my class path contains a reference to the current location (".") for the MyProgram.java file, and it contains a reference to the classes folder ("./classes/") which is the base location for the org.somepackage package inside whose subfolders (./classes/org/somepackage/) on can find the Human.class file.
At this stage, I was simply expecting the java engine to compile MyProgram.java into the program MyProgram.class - but, instead, I get an error:
MyProgram.java:1: error: package org does not exist
I've been following the instructions listed here:
https://www3.ntu.edu.sg/home/ehchua/programming/java/J9c_PackageClasspath.html
and I don't appear to be deviating from the instructions - yet I'm unable to locate an explanation on Stackoverflow or anywhere else as to a possible reason for this compile failure. If anyone has an idea, your help would be very much appreciated.
Thanks,

Your mistake is here
import org.somepackage; <--
public class MyProgram {
public static void main(String arguments[]) {
System.out.println("Programme up and running...");
Human myHuman = new Human();
myHuman.scream();
}
you forgot to import class actually, you need to write this name
import org.somepackage.Human; import all package content import org.somepackage.*; or write full qualified name of class in your code
org.somepackage.Human myHuman = new org.somepackage.Human();
myHuman.scream();
correct mistake:
import org.somepackage.Human;
public class MyProgram {
public static void main(String arguments[]) {
System.out.println("Programme up and running...");
Human myHuman = new Human();
myHuman.scream();
}
after that compile your Human.java by this command:
javac -d classes Human.java
and MyProgram.java
javac -d classes -cp "classes" MyProgram.java
and run MyProgram by
java -cp "classes" MyProgram

Getting the following error - No suitable driver found for jdbc:postgresql://localhost: 5432/testDBMS

I get back an error indicating java.sql.SQLException: No suitable driver found for
jdbc:postgresql://localhost:
5432/testDBMS
import java.sql.*;
import java.util.*;
public class JdbcPostgresqlConnection {
public static void main(String[] args) {
Connection conn3 = null;
try {
String dbURL3 = "jdbc:postgresql://localhost:5432/testDBMS";
Properties parameters = new Properties();
parameters.put("user", "pgmrHere");
parameters.put("password", "111111");
conn3 = DriverManager.getConnection(dbURL3, parameters);
}
catch (SQLException ex) { ex.printStackTrace(); }
}
}

java -cp . JdbcPostgresqlConnection
So, clearly, the only thing that is in the classpath is the current directory (.). The postgresql driver jar is not. You need to add it to the classpath:
java -cp .:/path/to/driver.jar JdbcPostgresqlConnection
on Linux/MacOS, or
java -cp .;c:\path\to\driver.jar JdbcPostgresqlConnection
on Windows.

The syntax to compile was - java -cp .;"C:\Program Files\PostgreSQL\9.3\lib\postgresql-9.3-1102.jdbc4.jar" JdbcPostgresqlConnection. Note 2 things; the quotes around the jar specification and the jar files cannot be in a folder with a space in the name. This is normally not the case on *nix system, but is often encountered in Windows systems. Note too, that when I put the jar file in the same folder with the java program I could eliminate the double quotes - java -cp .;C:\AZ_Fantasy5\postgresql-9.3-1102.jdbc4.jar JdbcPostgresqlConnection. Special thanks to JB Nizet for pointing out this situation.

As the error says java -cp . JdbcPostgresqlConnection java.sql.SQLException:
No suitable driver found for jdbc:postgresql://localhost: 5432/testDBMS
Which means you didnot include the postgresql.jar in your classpath
Try executing like this and I'm assuming it is Windows OS by seeing your error
java -cp .;pathOfYourDriverjar/postgresql.jar JdbcPostgresqlConnection

Did you not load the driver in your code? Either define the jdbc.drivers property setting it to org.postgresql.Driver or add Class.forName("org.postgresql.Driver") to your code.

Enthuware Mock-20 Confusion -classpath and packages

I am using enthuware to practice mock questions for classpath and packages. Here is the question.
//in file ./Foo.java
public class Foo {
public static void main(String[] args) {
System.out.println("In Foo");
}
}
//in file ./com/Foo.java
package com;
public class Foo {
public static void main(String[] args) {
System.out.println("In com.Foo");
}
}
Which of the given statements are correct assuming that the command lines are executed from the current directory with default classpath set to ./classes?
The options given are
Executing java -classpath .:./com Foo will print "In com.Foo"
Executing java -classpath ./com:. Foo will print "In com.Foo"
Executing java Foo will print "In com.Foo"
java -classpath . com.Foo will not execute.
Executing java -classpath ./com:. com.Foo will print "In com.Foo"
Correct option given is option-5. The strange problem is when i try to execute option-5 from my command line it gives me the following error.
Can someone tell me what is wrong? I am not able to figure out the reason. Plus what does this
./com classpath mean?
Command Change
I noticed one strange thing, if i change the classpath and run the command as
java -classpath . com.Foo
It states in com.Foo. As soon as i change the command to add this path ./com. It gives the above mentioned error.
Thanks.

The "./com" is a relative path to the current path.
If you have your class in [current_path]/com/Foo.class
You can run your class with the following command:
java -classpath ./com com.Foo
If you are in the com folder [current_path: com]/Foo.class you can execute the following command:
java -classpath . com.Foo

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();
}
}