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How can I solve that type of issue when I compile using `javac`: " error: cannot find symbol [...]"?

For starters, I have to say that I am using IntelliJ IDEA Community Edition 2020.3.1 and running java 15.0.1 2020-10-20, also when I run my program after enabling assertions and clicking on the run button, it works as expected. That being said here is my file structure:
Here is the code in my TestRunner.java file:
import java.lang.reflect.Method;
import java.net.URL;
import java.net.URLClassLoader;
import java.nio.file.Path;
import java.util.ArrayList;
import java.util.EnumMap;
import java.util.List;
import java.util.Map;
public final class TestRunner {
private static final List<Class<?>> TESTS = List.of(CalculatorTest.class);
public static void main(String[] args) throws Exception {
List<String> passed = new ArrayList<>();
List<String> failed = new ArrayList<>();
for (Class<?> klass : TESTS) {
if(!UnitTest.class.isAssignableFrom(klass)){
throw new IllegalArgumentException("Class "+ klass + " must implement UnitTest");
}
for(Method method : klass.getDeclaredMethods()){
if(method.getAnnotation(Test.class) != null){
try{
UnitTest test = (UnitTest) klass.getConstructor().newInstance();
test.beforeEachTest();
method.invoke(test);
System.out.println(method.invoke(test));
test.afterEachTest();
passed.add(getTestName(klass, method));
}catch(Throwable throwable){
failed.add(getTestName(klass, method));
}
}
}
}
System.out.println("Passed tests: " + passed);
System.out.println("FAILED tests: " + failed);
}
private static String getTestName(Class<?> klass, Method method) {
return klass.getName() + "#" + method.getName();
}
}
Here are my issues:
When I compile my main class TestRunner.java using javac TestRunner.java, it fails to find those symbols CalculatorTest.class, UnitTest.class, Test.class, UnitTest. Here is the error message:
When I use javac *.java though, my files compile and my .class files are generated, here is a screenshot:
but when I try to run my file using java TestRunner it says: "Error could not find or load class TestRunner, here is a screenshot:
If anyone can help me solve those issues I'd would be very happy. So far, I have found no solutions when I googled about them. Thank you!

After reading many answers, I found that the solution was simple.
First compiling TestRunner.java:
javac -cp . TestRunner.java
Then running TestRunner (containing my main function):
java -cp . -ea TestRunner
It turns out I was missing on the dot "."!
Here is the final result:

Compile Error: Package sqlj.runtime does not exist

I am trying to do a homework assignment in a database course that requires me to use sqlj. It is supposed to make a connection to a SQL database running on my computer. When copying and pasting the example code into Netbeans I get a compile error:
package sqlj.runtime does not exist: import sqlj.runtime.*;
import java.sql.*;
import java.io.*;
import sqlj.runtime.*;
import sqlj.runtime.ref.*;
import oracle.sqlj.runtime.*;
public class A10Q1 {
public static void main(String[] args) {
DefaultContext cntxt = oracle.getConnection("url", "user", "pswd", true);
}
}
I changed the inputs on the getConnection function.

Java program not working using the command line

Short story :
When I run my java application through the Intellij it's all working.
When I run it through the command line I have some issues.
Long story:
First, I have to say that I have a 'lib' folder inside my project with all the Jars I need and I added it as a Library to the project.
When I compile it from the command line I have to specify a '-cp' to the lib folder, otherwise it doesn't load the jars. Even though it looks good, when I run my java application, I get a 'Error: Could not find or load main class awsUpdater' error
My commands :
For compiling -
javac -cp "../../../../lib/*" awsUpdater.java
For executing -
java -cp "../../../../lib/*" awsUpdater
Here's my class (besides the methods)
package AWSUpdater;
import com.amazonaws.AmazonClientException;
import com.amazonaws.AmazonServiceException;
import com.amazonaws.auth.DefaultAWSCredentialsProviderChain;
import com.amazonaws.services.s3.AmazonS3;
import com.amazonaws.services.s3.AmazonS3Client;
import com.amazonaws.services.s3.model.GetObjectRequest;
import com.amazonaws.services.s3.model.PutObjectRequest;
import com.amazonaws.services.s3.model.S3Object;
import java.io.*;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
public class awsUpdater {
public static void main(String[] args) throws IOException {
String bucketName = "bucket";
String key = "ket";
//AmazonS3 s3Client = new AmazonS3Client(new ProfileCredentialsProvider());
AmazonS3 s3Client = new AmazonS3Client(DefaultAWSCredentialsProviderChain.getInstance());
System.out.println("Downloading an object");
S3Object s3object = s3Client.getObject(new GetObjectRequest(
bucketName, key));
//Get new version of android
String newAndroidVersion = getNewAndroidVersion();
//Download current versions.json
String currentJson = displayTextInputStream(s3object.getObjectContent());
//Edit versions.json with new android version
String editedJson = editJsonWithCurrentAndroidVersion(currentJson, newAndroidVersion);
//String editedJson = editJsonDummyCheck(currentJson);
//Create new file to upload to S3
createFileWithNewJson(editedJson);
//Upload new file to S3
updateVersion(bucketName, key, "versions.json");
}
Would appreciate any help with how to compile and execute my program through the command line. thanks !

you need to add package name
java -cp "../../../../lib/*" AWSUpdater.awsUpdater

I notice that the class awsUpdater is under the package AWSUpdater, so you can not use java -cp "../../../../lib/*" awsUpdater directly.
For Example:
I create a project like this:
|-test
|-AWSUpdater
|-awsUpdater.java
Detail of the awsUpdater.java:
public class awsUpdater {
public static void main(String[] args) {
System.out.println("hello");
}
}
then(now I'm in test/AWSUpdater):
javac awsUpdater.java
java awsUpdater
Everything goes well!
If I add the class to the package, like this:
package AWSUpdater;
public class awsUpdater {
public static void main(String[] args) {
System.out.println("hello");
}
}
then(now I'm in test/AWSUpdater):
javac awsUpdater.java
java awsUpdater
here, it will got the error which is same with yours.
Now, you can go to the package's root dir. (here is test), and then:
javac AWSUpdater/awsUpdater.java
java AWSUpdater/awsUpdater
Now, you will get the correct result.

Error: Could not find or load main class using external libraries

I am trying to execute a java program I wrote. Doing the compiling is no problem ( I used : javac -cp \* *.java). But when i try to run it (using: java -cp \* FirstTestCase 1 1 data), it says Error: Could not find or load main class FirstTestCase.
this is the code:
import java.io.BufferedReader;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.security.cert.CertificateException;
import java.security.cert.CertificateFactory;
import java.security.cert.X509Certificate;
import java.util.Timer;
public class FirstTestCase {
public static void main(String[] args) throws IOException, InterruptedException, CertificateException {
// TODO Auto-generated method stub
int amount = 100000;
int threads = 150;
String file = "newData";
if(args.length == 3)
{
amount = Integer.parseInt(args[0]);
threads = Integer.parseInt(args[1]);
file = args[2];
}
X509Downloader d = new X509Downloader(amount, threads, file);
d.getCertificates();
}
}
We are also using external libraries, 4 to be precise. We use the -cp \* to include them all. When i run java FirstTestCase 1 1 data it succeeds to run it but then throws Exception about it not finding the classes that we use from the external libraries.
I normally use an IDE and therefore i barely have any experience using the terminal to start java programs.
I do use a Mac at the moment to test it, but we will run this program later on a server using Linux (in case the operating system matters)

why i am not able to read Html Content from a website in a file?

I have made a java program where in i can use any website to read its Html Content using Scanner class and Varargs.I am not able to get the output while i am using Scanner class and VarArgs.
Below is the following Code.
import java.io.FileWriter;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.URL;
import java.util.Scanner;
public class ReadWebsite
{
public static void main(String[] args) throws Exception
{
URL oracle = new URL(args[0]);
Scanner s=new Scanner(oracle.openStream());
while (s.hasNext())
{
System.out.println(s.nextLine());
}
s.close();
}
}
OutputShown
Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 0
at oodlesTech.ReadWebsite.main(ReadWebsite.java:15)

if you are running from eclipse you have to pass the arguments.
right click program - > run as - > run configurations -> arguments ->program arguments . in this tab pass the actual url which will be passed as args[0] to your main method.

You are not passing the argument to your java program.
For your testing you can either hard code it in code e.g. URL oracle = new URL("http://www.google.com"); or pass an argument to your java program, explained here