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How to add a dependency to module path?

I am very new to programming, and while working on my first software development project I came across the error: "package javax.activation is not visible." I have read other posts that have said that in order to fix the error, one must add a dependency to the module path?
Because I'm just starting out, I really don't know what this means and how to go about that, and was wondering if someone could point me in the right direction? Thanks in advance. (I'm also using JGrasp if that matters)

Broadly speaking, a dependency is code (often written by someone else) which your application needs to compile.
A dependency in your case, is a java library which has classes that need to be on your class path. You can find more about class paths here: https://docs.oracle.com/javase/tutorial/essential/environment/paths.html. In order to overcome error mentioned in a question, you need to have javax.activation module dependency on your class path.
You could do it in few ways. In the majority of IDEs (in your case we are talking about JGrasp) there is a way to add a dependency to the project directly. Then, your IDE would compile the code with given dependency on a class path and problem would be solved. And that would be the first and most beginner-friendly way, unfortunately I haven't a faintest idea about JGrasp so I'm going to focus on other solutions.
The second way you could do this is to build your program with build automation tool, such as Apache Maven or Gradle. You should definitely check those guys out, as they are insanely useful when it comes to building Java code and, sooner or later, you will probably start using them anyway. Let's say you have chosen Apache Maven. In your project you would then have a pom.xml file and you would simply look-up the needed dependency in Maven Central repository, add it to your dependencies section in pom.xml file and build the application. Your pom would look something like this:
<project>
...
<dependencies>
<!-- https://mvnrepository.com/artifact/javax.validation/validation-api -->
<dependency>
<groupId>javax.validation</groupId>
<artifactId>validation-api</artifactId>
<version>2.0.1.Final</version>
</dependency>
</dependencies>
...
</project>
Of course Apache Maven is not a lightweight tool so you would have to take some time to learn how to build code with it. I recommend starting with this tutorial:
https://maven.apache.org/guides/getting-started/maven-in-five-minutes.html
I also encourage you to get your hands on Apache Maven docs, as it is quite readable and transparent.
And the last way I can think of is to manually compile your application and include the required dependency during the compilation process. There are plenty of tutorials on SO that tell you how to do this, so I'll simply summarize and indicate the resources. What you need to do is to find the required dependency jar package. You will want to search the maven central repository (see: https://mvnrepository.com/) and from there download your .jar file. The next thing you need to do is to learn how to compile your Java code to .class files including the downloaded jar. To acquire such a wonderful skill, please see this one: How to include jar files with java file and compile in command prompt
Amongst those three ways, the recommended one is to get to know with build tools such as Apache Maven or Gradle. Hope I helped you! Good luck

How to import git java project to Eclipse

I've tried every option explained step by step here and here: and here
And I can't get it to work.
What I want to do is pick this project: , however it may be done (I've tried both through maven and git), and use its code in eclipse. And what I mean by that, is that I get to the point of seeing the folders in eclipse, but I can't create packages since it's not a java project, and if I mess up the code on the files that appear, it doesn't give me a warning nor in general interacts with said code.
So I guess I'm missing some piece of knowledge and I don't know where else to look for it. What should I do to use that project in my eclipse, and create my own code that calls and uses the classes and methods from said project?
Thank you in advance.

Just download it with git, then import it as a maven project. If this fails, create new "java project from existing sources", pointing as a source the simmetrics-core/src and simmetrics-example/src directories. If it fails, point separately simmetrics-core/src/main, simmetrics-core/src/test etc.

Since this artifact is present in the maven repository (https://mvnrepository.com/artifact/com.github.mpkorstanje/simmetrics/4.1.1), you can create your own new maven project in Eclipse and add simmetrics as a dependency to it in its pom.xml file
<dependency>
<groupId>com.github.mpkorstanje</groupId>
<artifactId>simmetrics</artifactId>
<version>4.1.1</version>
</dependency>
This will put simmetrics to the classpath of your own project and you should be able use its API

Getting Spring (and other libraries) in a Maven world

I am following an online tutorial, and am stuck trying to get Spring libraries to run things with. The instructions are either a little out of date or assume I know how to do things in a Maven world that I do not.
They give web addresses on the Spring site from which they say I can "download the jars". But you can't download jars from any of them; evidently what you can do is find pom.xml fragments and use them to download jars. If you know how.
For example: the tutorial says:
Finally, following is the list of Spring and other libraries to be
included in your web application. You simply drag these files and drop
them in WebContent/WEB-INF/lib folder.
commons-logging-x.y.z.jar
org.springframework.asm-x.y.z.jar
org.springframework.beans-x.y.z.jar
org.springframework.context-x.y.z.jar
org.springframework.core-x.y.z.jar
org.springframework.expression-x.y.z.jar
org.springframework.web.servlet-x.y.z.jar
org.springframework.web-x.y.z.jar
spring-web.jar
I love the "simply" here.
I have many but not all of these (version 3.2.4). I have googled the library names and used jarfinder for the ones I don't have, but haven't found them all. It seems to me I'm flailing around a bit, just trying this and that until something works. I hate that.
I'm hoping someone can give me a set of steps I should follow when faced with this sort of thing, since we're faced with it all the time. Do I need to stop my current study of programming and learn Maven inside and out so that I can configure the bloody system so I can program again?

Is it a maven project you have?
If so in the pom.xml you just need to place the “pom fragments” in the xml.
i.e. between the dependencies tags. For example,
<dependencies>
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>4.8.2</version>
</dependency>
</dependencies>
Once you have done that run maven install. Under Eclipse it is: run as > maven install.
That will download all the dependences i.e. jars you have listed into the you local maven repository.
I think the default is C:\Users\yourName\.m2\repository

Found most of the needed jar files here:
http://www.java2s.com/Code/Jar/CatalogJar.htm
while I downloaded commons-logging here:
http://mvnrepository.com/artifact/commons-logging/commons-logging/1.2

My advice is, stop study you program language, Java I guess and learn how to integrate maven dependencies of Spring in your Maven project.
http://spring.io/blog/2009/12/02/obtaining-spring-3-artifacts-with-maven/
You cannot start the house from the roof

Which JAR does Java pick for a certain import?

Dependency issues, we've all dealt with them, but I'm mostly used to C# and now working in Java so I have some questions.
Let's say I add a library to my project, called ExtLib.
ExtLib has a certain library included in its lib-folder, let's call it LogLib-1.0.
I'm using Eclipse and I've made a User Library for ExtLib, included its main jar file and all of the files in its lib-folder. So far so good.
But now I want to do some logging of my own, so I make another User Library and add the newer LogLib-1.1 to it, because it has some new features I want to use.
Can I ever be sure I'm not breaking ExtLib this way?
I know .NET uses the Global Assembly Cache and methods like that, but I have no clue how Java handles this. I tried Googling, but didn't find much, a few mentions of the Classloader here and there, but nothing helpful.
Can anyone tell me what a proper way to deal with this issue is? Or is it no issue at all?

In this specific case (LogLib-1.0 and LogLib-1.1) we're dealing with the same library that is both a direct dependency of your application, and a "transitive" dependency via the ExtLib. In this situation, dependency management can come to help.
It will probably reason that LogLib-1.1 is a backward compatible release of LogLib-1.0, and it will decide that your application can run fine using only LogLib-1.1.
In the Java world, tools like Maven, Gradle or SBT exist to help you in this. Maven is the most widespread, and other tools often are compatible with Maven.
Usage
To solve this situation using Maven, you would add a file called pom.xml to your application, stating it depends on LogLib version 1.1. That might look like this (note that this example is pure fiction):
<dependency>
<groupId>org.loglib</groupId>
<artifactId>loglib</artifactId>
<version>1.1</version>
</dependency>
The ExtLib you're using also has a pom.xml shipped with it, and it might state
<dependency>
<groupId>org.loglib</groupId>
<artifactId>loglib</artifactId>
<version>1.0</version>
</dependency>
Maven (or any other tool) would decide that including LogLib-1.1 is sufficient to get your application running. When using Maven, mvn depedency:tree helps you visualise that.
Deployment
With respect to the packaging / deployment question: mvn package will package your application to a jar, war or ear archive, including only the dependencies you need (and not two versions of the same lib). This makes you don't have to worry about the order in which your application server reads the jar files.

How do I add/use an embedded SQLite in a Java project?

I'm trying to add an embedded database to my application, but I have no clue where to begin. So far I've found that I should download the sqlite-jdbc driver and add the .jar to my project. From there I'm kind of lost, are there any good tutorials to get me started or some helpful tips?
Also, I'm using Eclipse for my IDE, so if there's anything within there that will simplify the process, feel free to add that as well!

You want dependency management here? Read up on Maven (very easy), write a Maven pom.xml file and load it into Eclipse that way. Eclipse and NetBeans understand Maven very well now. No need to learn an Eclipse-specific way to do this since Maven will work as well in NetBeans as Eclipse and is simple to run on the command line too.
Based on what search.maven.org says, your dependency in Maven would be this added to a standard pom file to get the latest:
<dependency>
<groupId>org.xerial</groupId>
<artifactId>sqlite-jdbc</artifactId>
<version>3.7.15-M1</version>
</dependency>