Develop Reference

Building an eclipse plugin. What dependency and which class could I extend to implement warning signs in Java and Effective pom files for a project?

I am a bit new to eclipse plugin development. My requirement:
I want to show warning signs(like screenshot attached) in the import statements Java files and effective pom files of Java projects based on some parameters.
Assuming eclipse already has some classes and functions for this, I would like to know what dependencies I could add in my Manifest file of my Eclipse Plugin and which class I could extend and functions I could use to implement my requirement?
Any help would be very much appreciated. Thank you.

If you're willing this to happen at same time as compilation, you can add an extension to the org.eclipse.jdt.core.compilationParticipant extension point ( https://help.eclipse.org/2019-12/index.jsp?topic=%2Forg.eclipse.jdt.doc.isv%2Freference%2Fextension-points%2Forg_eclipse_jdt_core_compilationParticipant.html ) and implement the CompilationParticipant.reconcile() method to look at the content of the file and use putProblems() to add problems.
You can also put it in a separate builder ( https://help.eclipse.org/2019-12/index.jsp?topic=%2Forg.eclipse.platform.doc.user%2Freference%2Fref-5.htm ), or resource listener, or document listener, that would invoke file.createMarker(...) to add the error markers.
All that depends on which layer you prefer to hook onto.

How to get IntelliJ IDEA 2017.2 to offer suggestions on importing the right packages to resolve symbols?

How do I get IntelliJ IDEA to offer suggestions to resolve an unresolved symbol like Visual Studio does like in the picture below?
I wanted to use Aspose Cells for Java in a console application, so I downloaded the relevant JAR file and added a reference to it like so:
File -> Project Structure -> Dependencies Tab -> + sign
I am not sure why I do not see the library reference in the External Libraries node of the treeview on the left side.
Anyway, just because I wasn't sure, I also added the JAR files I needed to a newly created folder which I named lib and added that lib folder as a library like so:
Now, when I type in some code, the intellisense reports that it cannot resolve the symbol Workbook.
So, I qualify the type Workbook with its full name like so:
com.aspose.cells.Workbook and that symbols is resolved. To resolve all the symbols, I add the import com.aspose.cells.* statement on the top and the symbols are all resolved.
I was wondering why, like Visual Studio offers a suggestion for you to add the namespace on the top, does IntelliJ IDEA 2017.2 not give me suggestions to add the relevant import statement so I don't have to type it myself or even know what the correct import statement is?
Does it have such a feature? How do I use that feature?

I think you need to move the red line(Error line).
Press alt+Enter, then choose import class or(Something like this);

How can I create and Import Libraries in Netbeans - A Full Documented Q

It's me again. So here's the deal, I still don’t really grasp if I am doing something wrong.
I am trying to create my own Personal Library, in which I have certain string methods and so on.
I’ve started by creating a new Project as a Java library:
Then I've added a package to that library:
After that I've created a class in said package:
Here the code of my class:
And cleaned and built that Class//Library. Run -> Clean and Build
And afterwards created the JavaDoc Run -> Generate JavaDoc(MyTestLibrary)
After doing this i decided to add my newly created Library to the Libraries under Tools - > Libraries:
After that I’ve added a new Library (bottom right) and named it TestLibrary:
SO decided to add the .jar File first. I clicked on the “Add JAR/Folder... ” Option and searched for my Projekt Folder (from MyTestLibrary) and went in to the “dist” folder and selected the .jar file:
After that I’ve added the “src”-Folder in “Sources” and the “javadoc”-Folder in “Javadoc”.
After i was finished it was time to create a new Project, to be precise a new Java Application, and try to import my freshly created library. I rightclicked on Libraries and clicked on “Add Library...”:
And imported my Test Library and adding it:
Happy that I've added my Library to my application I decided to import it
import TestPackage.TestClass;.
If I try
public static void main(String[] args)
{
TestClass.
}
The only suggestion is TestClass.class and not TestClass.TestMethod.
Why can't I access the methods of the “TestClass” directly?
How can I see them?
I've tried being as specific as possible. I hope this time I can fully understand what is going on and why I can't access them.

The solution was fairly simple and obvious.
To access the methods without the need of creating an instance of the class i just had to declare them static.

Any way (or shortcut) to auto import the classes in IntelliJ IDEA like in Eclipse?

In Eclipse, while coding in Java and press Ctrl + Shift + O auto import all the Classes automatically.
In NetBeans, this is done with Ctrl + Shift + I.
Is any way to do this in IntelliJ IDEA?
I searched an equivalent shortcut in google, StackOverflow, IntelliJ IDEA configuration and in the official IntelliJ website Keyboard Shortcuts You Cannot Miss

IntelliJ IDEA does not have an action to add imports. Rather it has the ability to do such as you type. If you enable the "Add unambiguous imports on the fly" in Settings > Editor > General > Auto Import, IntelliJ IDEA will add them as you type without the need for any shortcuts. You can also add classes and packages to exclude from auto importing to make a class you use heavily, that clashes with other classes of the same name, unambiguous.
For classes that are ambiguous (or is you prefer to have the "Add unambiguous imports on the fly" option turned off), just type the name of the class (just the name is OK, no need to fully qualify). Use code completion and select the particular class you want:
Notice the fully qualified names to the right. When I select the one I want and hit enter, IDEA will automatically add the import statement. This works the same if I was typing the name of a constructor. For static methods, you can even just keep typing the method you want. In the following screenshot, no "StringUtils" class is imported yet.
Alternatively, type the class name and then hit Alt+Enter or ⌥+Enter to "Show intention actions and quick-fixes" and then select the import option.
Although I've never used it, I think the Eclipse Code Formatter third party plug-in will do what you want. It lists "emulates Eclipse's imports optimizing" as a feature. See its instructions for more information. But in the end, I suspect you'll find the built in IDEA features work fine once you get use to their paradigm. In general, IDEA uses a "develop by intentions" concept. So rather than interrupting my development work to add an import statement, I just type the class I want (my intention) and IDEA automatically adds the import statement for the class for me.

Not all at once. But you can press
Alt + Enter
People assume it only works when you are at the particular item. But it actually works for "next missing type". So if you keep pressing Alt + Enter, IDEA fixes one after another until all are fixed.

I think the best solution, though not exactly the same as Eclipse/Netbeans, is to change the 'Optimize Imports' settings.
Under Preferences > Editor > General > Auto Import
Set Add unambiguous imports on the fly
Edit: Using this method, when there are ambiguous imports, IntelliJ will let you know, and you can then use Alt + Enter method outlined in the answer by Wuaner
I find that, almost always, the most appropriate Import is at the top of the list.

Can't import all at once but can use following combination:
ALT + Enter --> Show intention actions and quick-fixes.
F2 --> Next highlighted error.

Seems like IntelliJ IDEA will import missed class automatically, and you can import them by hit Alt + Enter manually.

Another option is to ask IDEA to behave like eclipse with eclipse shortcut keys. You can use all eclipse shortcuts by enabling this.
Here are the steps:
1- With IDEA open, press Control + `. Following options will be popped up.
2- Select Keymap. You will see another pop-up. Select Eclipse there.
If you don't see "Keymap" in the options, install "Eclipse Keymap" plugin
3- Now press Ctrl + Shift + O. You are done!

Use control+option+L to auto import the package and auto remove unused packages on Mac

Use Alt+Enter for importing a single package or use Alt+Shift+Enter to auto import all the unambiguous packages in the current file.

UPDATE
#ntg has given a very smart solution for converting import .* to individual imports in existing files (it is not completely automatic, but still quite low-effort)
Go to any import .* statement and press Alt Enter (⌥ return on Mac)
a popup will appear to replace the * import with individual imports
then just hit Enter again
Original answer
Not sure if this is universal but I've found that after enabling both the following settings (as told in earlier answers), my IntelliJ is able to smartly convert package.* imports into individual imports (in existing files) just by deleting the import com.company.package.* line
Add unambiguous imports on the fly
Optimize imports on the fly
Essentially it will be able to add all 'unambiguous' imports for us, the rest will have to be resolved manually
I'm using
IntelliJ IDEA Ultimate 2022.1 (Build #IU-222.3739.54)
MacOS Monterey 12.5.1

Hover on top of the code which needs a class then press
alt + shift + Enter
This will auto import the needed class.

Use control+option+O to auto-import the package or auto remove unused packages on MacOS

Error: Could not find or load main class in intelliJ IDE

I'm a beginner in Java and am trying to run my code using IntelliJ that I just installed as my IDE with JDK 1.7. The following piece of code keeps does not even compile and keeps giving me the error:
Error: Could not find or load main class libTest
Code
import java.lang.Integer;
import java.lang.String;
import java.lang.System;
import java.util.*;
class book {
private String name = "trial";
private int bookCode=1;
private int issued=0;
public void Issue(){
if(issued==0) {
issued=1;
System.out.println("You have succesfully issued the book");
}
else {
System.out.println("The book is already issued. Please contact the librarian for further details");
}
}
public int checkCode() {
return bookCode;
}
String readName() {
return name;
}
public void setName(String newName){
name=newName;
}
public void setBookCode(int newCode){
bookCode=newCode;
}
}
class library {
private ArrayList books=new ArrayList();
public void getList(){
for(int bk:books){
String bName=books(bk).readName();
System.out.println((bk+1)+") "+bName);
}
}
}
public class libTest{
public static void main(String[] args){
library newLib= new library();
System.out.println("code working");
}
}
Is there any change that i have to make in the compiler settings?? Or is it the code.

This might help:
1) "Build" menu -> "Rebuild Project".
Sometimes Intellij doesn't rewrite the classes because they already exist, this way you ask Intellij to rewrite everything.
2) "Run" menu -> "Edit configuration" -> delete the profile -> add back the profile ("Application" if it's a Java application), choose your main class from the "Main Class" dropdown menu.
3)"Build" menu -> "Rebuild Project".

If none of the above answers worked for you, just close your IntelliJ IDE and remove the IntelliJ IDE file and folder from the root of your project:
rm -rf .idea *.iml
Then open the project with IntelliJ. It must work now.

For me the solution was to fix the output directory under project settings. Before I was using just "target" for the Project compiler output. Instead I updated it to have a full path e.g. D:\dev\sigplusjava2_68\target

I had this problem and I tried everything under the sun that I could think of and on this site.
None of my Java classes were being picked up after I pulled from a remote branch. All the classes had red Js by their names in the Project Hierarchy, not blue Cs.
In the end, I tried to follow this tutorial and a few steps in tried something not described and fixed the issue:
https://www.jetbrains.com/help/idea/creating-and-managing-modules.html
Here's what I did:
Goto File | Project Structure, or press Crtl+Shift+Alt+S
Select Modules under the Project Settings section.
In the Sources tab click Sources on the 'Mark as:' line.
Click the Apply button.
For some reason, all my classes then had blue C's.
Someone with a better understanding of how IntelliJ and/or IDE's might be able to explain the phenomenon, but all I know is now it can see all the classes and more importantly the main one, and run.

Invalidate cache and restart your IntelliJ, it worked for me.

Explicitly creating an out folder and then setting the output path to C:\Users\USERNAME\IdeaProjects\PROJECTNAME\out
seemed to work for me when just out, and expecting IntelliJ to make the folder wouldn't.
Also try having IntelliJ make you a new run configuration:
Find the previous one by clicking
then remove it
and hit okay.
Now, (IMPORTANT STEP) open the class containing your main method. This is probably easiest done by clicking on the class name in the left-hand side Project Pane.
Give 'er a Alt + Shift + F10 and you should get a
Now hit Enter!!
Tadah??
(Did it work?)

File > Project Structure > Modules > Mark "src" folder as sources.
This should fix the problem. Also check latest language is selected so that you don't have to change code or do any config changes.

I know this was asked a while ago, but I was just stumbling over this issue and thought my findings might help others. As pointed out, the error message is basically a result of the out folder. That's because, when you're trying to run the program, it compiles the code first, and puts the compiled result to the out location, and then it tries to load the compiled code from the out location. If the compiled code is not in the location expected, you'll get the error.
The point I'm particularly wanting to share is that some times, the code is not compiled (built), even though your run configuration specifies "Build" in the "Before launch" section of the configuration panel.
When can this happen?
One situation that can cause this to happen is if you're using modules and you manually delete the module out directory. For example, if I have a module named "foo", there should be a directory named foo under out/production. If you manually delete it, the build system may not know that it needs to be rebuilt.
Even worse, if you select Build | Build module 'foo', it still may not rebuild the module. If that's the case, you should select a file in the module, for example 'bar.java' and then select Build | Recompile 'bar.java'. Now the out directory out/production/foo should be restored.
Since IntelliJ typically knows about any changes going on, this surprised me, and took me a little time to figure out, so I thought I'd share.

Check your class module : I have encountered this problem with intellij :
I have a maven multi-module project, the problem is that i runing a class which not exist the module within the configuration, so my problem is fixed by setting the right module ("edit configuration" -> "use class of module")
may this help you

I had to mark the "src" folder as "Sources". After restarting IntelliJ and rebuilding the project I could run the project without further issues (see screenshot).
Edit: You can access the "Project Structure" tab via File->Project Structure or by pressing Ctrl+Shift+Alt+S.

I ran into this problem when my Java class was under src/main/kotlin. After I moved it to src/main/java, the problem was gone.

I have faced such problems when the class is in the default folder, i.e. when the class does not declare a package.
So I guess using a package statement (eg. package org.me.mypackage;) on top of the class should fix it.

Open Modules Tab (Press Ctrl+Shift+Alt+S). I had two modules under one project. I've solved the problem after removing the second redundant module (see screenshot).

After creating your project in intelliJ, try running the following command:
mvn package

I have tried all the hacks suggested here - to no avail. At the end I have simply created a new Maven application and manually copied into it - one by one - the pom.xml and the java files and resources. It all works now. I am new to IntelliJ and totally unimpressed but how easy it is to get it into an unstable state.

Invalidating cache didn't work.
I edited the main class java file with a dummy change and ran it. It worked.

In my case the problem seemed to be related to upgrading IntelliJ. When I did this I overwrote the files from the old IntelliJ with the files from the new IntelliJ (2017 community to 2018 community). After that all of my projects were broken. I tried everything in this thread and none of them worked. I tried upgrading gradle to the latest version (4 to 4.8) and that didn't work. The only thing that worked for me was deleting the entire IntelliJ folder and reinstalling it. All of my projects worked after that.

I have tried almost everything suggested in the answers here, but nothing worked for me.
After an hour of just trying to run my application, I noticed that my project's path included non-ASCII characters (Arabic characters). After I moved my project to a path with no non-ASCII characters, it executed just fine.

Goto File-> Invalidate Caches and Restart .
Else delete rm -rf .idea *.iml
and restart InteliJ

You can run the maven command on the pom.xml file in your project directory:
mvn clean install

For me - i tried few of the options above, did not work. Then i just renamed my Application class and that probably forced intelliJ to build a fresh jar and error message started to change. Then i renamed it back and it worked.

Mark the directory as a source directory. Opened via Ctrl+Shift+Alt+S

modules.xml with wrong content, I don't know what's matter with my IDEA.

I inherited a bunch of .JAVA files from elsewhere and couldn't figure out how to get them to work in any IDE. Ultimately I had to go to the command line where the Main.JAVA file was and run javac Main.java. This created a bunch of .CLASS files. The IDE's were then able to figure out what to do.

I got this error when using Scala/SBT. IntelliJ could not find the main class, even though everything was set up correctly.
My solution: delete the <user>/.sbt/<version>/plugins/target folder, then restart IntelliJ.

You probably would have specified a wrong package and the package hierarchy would not be right. Look below
The ide would highlight the wrong path in that case.

I'm using IntelliJ with Spring and my main class is wrapped in a JAR.
I had to mark the 'Include dependencies with "Provided" scope' in the Run/Debug configuration dialog

We are at File/Project Structure..
Answer might be:
Folder indicated as "content root" needs a child folder where the code is.
Plus find the button that marks code as excluded and not.
Not to be confused with tickbox that states excluded without telling in what phase and what**
Is it compiler exclude or runtime exclude? You are doomed to test and lot.
So no that tickbox but icons and colors.
As an idea we need to crack how it was originally thought to work. They never got it to work in first place and started add things in premature codaculation style.
It has been so many years and you cannot expect any improvement.
But as cure we can hack out some way to get it right every time.

Another thing you can check here is the actual command that is being passed to the JVM and make sure it looks OK. Scroll to the top of your Run console, it should be the first line.
Spaces in your Run Configuration VM Options field will malform the app startup command and can result in this error message
-DsomeArgument="arg with space must be quoted"

I am working with Kotlin but am guessing the problem is the same. I would start a project, create a single file and add main to it and the IDE couldn't find the main.
I tried the things in this list and none worked. I finally mentioned my frustration on one of the IntelliJ pages and was contacted. Of course, it worked fine for IntelliJ. After a couple of days back and forth, I noticed that the highlight function wasn't working and mentioned that. It turned out something was wrong with the IDE settings. I still don't know specifically what was wrong but the fix in my case was to reset the IDE settings. File->Manage IDE Settings->Restore Default settings.
After this, the green triangle start icon became visible to the left of my main function and things continued to work normally for subsequent projects.
Thanks to Konstantin at JetBrain's support for his patience.