Develop Reference

How I run individual java file in IDEA?

I am a java beginner, the first java IDE I downloaded was Visual Studio Code, it was very easy to use and everything is auto configured. But it kind overheats my laptop all the time, so I want to try IDEA, so far it's a very good experience, except when I open a java file and tried to run it in IDEA, it always pops out this run configuration window and I don't understand how to configure it. In visual Studio Code I can open any java file any time and run without any issues, but now I have to go through creating projects every time. Is there any solution for this?

From how the file icon looks:
your file is not recognized as the part of the sources of your project. Check the project settings to ensure that source directories are correctly set.
I'd also recommend you to look up and follow the conventions for the directory structure of java projects.
Once you've fixed the problem with sources, you'll see "run" icon next to your class, main method, or when you're right clicking the file.

Command-line
To run a single file, there is no need for an IDE.
In Java 11 and later, the java tool at the command-line can both compile and execute a single-file Java class. See JEP 330: Launch Single-File Source-Code Programs.
If your class named HelloWorld were in a file named HelloWorld.java, on a console type:
java HelloWorld.java
To be clear: The java command-line tool really only executes Java apps, while the javac command-line tool compiles Java source code. As a convenience, the java tool was enhanced to effectively call javac on your behalf for a single-file.
JShell
If you just want to run a few lines of Java, try JShell, the REPL tool bundled with Java 9 and later.
See:
Java Shell User’s Guide by Oracle
JEP 222: jshell: The Java Shell (Read-Eval-Print Loop)
Search to learn more and find tutorials.
BlueJ
Using an IDE such as IntelliJ, NetBeans, or Eclipse can be a daunting task for the new student of Java. Those IDEs are heavy-duty tools designed for professional programmers.
I recommend using an IDE designed for beginners. BlueJ comes to mind, designed specifically for educational purposes. BlueJ makes getting started with Java easier.
If you insist on using IntelliJ, read on.
If using IntelliJ, define a project
IntelliJ is not designed to work with single files. IntelliJ expects you to work within a project.
I strongly recommend learning the basics of Maven to create and drive your new project. By defining your project in Maven, the configuration is independent of any one IDE. You can move your project between major IDEs such as IntelliJ, NetBeans, and Eclipse.
Maven is also very useful for downloading needed libraries ("dependencies") that you may want to leverage in your work. And Maven is good at packaging your Java app as a JAR (or WAR or EAR).
In IntelliJ, choose "New Project". In the New Project window, click the Maven item on left. Check the Create from archetype box. Scroll the list to find item for org.apache.maven.archetypes:maven-archetype-quickstart. Under that, choose the "RELEASE" item. Click Next button.
In Name field, enter something like MyFirstProject. Click Next button.
On the Maven settings page, just click Finish.
Wait a moment for IntelliJ to download some stuff and configure your project. Eventually you should see a BUILD SUCCESS message in the Run pane.
You will also see a pom.xml file displayed. The POM contains your settings for Maven to run your project, in XML format.
Change the <maven.compiler.source> and <maven.compiler.target> elements to the version of Java you are using. The current version is Java 17.
After editing the pom.xml, look for a little floating windoid with a tiny Maven icon. Click the icon to have Maven process your changed POM. Wait a moment.
In the Project pane, navigate to the App file. There you see code to print “Hello World!”. Let's run that code now. Click the green triangle button on the left, in the gutter, next to the main method line. A pop-up menu appears offering a Run item. Choose that item to run the app immediately.
Down in the Run pane, you should see the results, the Hello World! text.
At this point you can add your single file to the org.example package seen in the Project pane.
By the way, you can change that package name by context-clicking and choosing Refactor > Rename….
Later, learn to use the Run/debug configurations feature of IntelliJ.
Know that you need not create a new project for each time you want to do a little experiment. Create one project for such experiments. Keep adding new .java class files for each experiment. Delete old class files you no longer need.
Eventually, I suggest updating the versions of various items in your POM. The QuickStart archetype is not configured for the latest versions (for reasons I cannot fathom).
And when you learn about unit testing, replace JUnit 4 in the POM with JUnit Jupiter (Aggregator) to use JUnit 5. One of the benefits of using Maven is that you can easily switch out dependencies such as going from JUnit 4 to JUnit 5.

The IDE needs to know what's called the entry point of the program, i.e. where to start running your code. That's what the "Edit Configuration" window is wanting you to do.
If your file "Lab3.java" is in a package, make sure to fully specify that in the field you have in red. Otherwise without knowing how your project is structured (as the other answer alludes to), it's difficult to pinpoint what we're missing here.

When you create your IntelliJ project, add a directory /src right at the root of your project. Right click on that folder and tell IntelliJ that you wish to mark it as a source root. The directory should turn blue in color.
Put your packages under /src. IntelliJ will know that those are Java files.
When you want to run a class with a main method, choose Run->Edit Configurations. Tell IntelliJ that you want to add an Application. It should prompt you with the classes that have main methods in them. You'll have no trouble running them.

Use Maven or Graddle. Make sure the project is configured with the build tool enabled and integrated, it will do basic things automatically. If you are not sure, please create a new project and add your files in. Steps:
Open the IDE
New Project
Choose from the left side bar "Maven" or "Graddle"
Give it a name and the location in your machine.
Click Finish
Now you have the project ready. You need the appropriate method to run in java. A main class. In IntelliJ you can just type "main" and the auto-complete will add it for you, make sure you inside the curly brackets of the class {}. More info about the main class. You seem to have this nailed down.
Lastly make sure you have a JDK installed in the IDE. I am pretty sure this is your issue here, make sure to use one of the option IntelliJ provides. A full guide from the developers is here and should satisfy your needs. I would suggest OpenJDK for a beginner, because that served me well at the beginning, at the end of the day its your choice.

How to set up Jacoco code coverage tool in Eclipse for viewing colors in Java code?

I have setup jacoco in jenkins as part of functional test job to generate code coverage report. But I feel its very tough to understand.
Somewhere I read that covered and uncovered lines of code are shown in colors in Eclipse. This is for functional tests which connect to a stage where the whole business logic has been deployed. This is present inside Eclipse also as part of the project. How to set it up?
What difference the setup has for unit tests?

You can download the Eclemma plugin from Eclipse marketplace.
Open Marketplace from Help menu.
Search for Eclemma Java Code Coverage.
Install and Restart Eclipse.
Right-Click on the project, select Coverage as -> JUnit Test

http://www.eclemma.org/userdoc/importexport.html mentions being able to import reports, but that they have to be exactly the same class files both when the report was generated and within the Eclipse workspace. It may work, it may not.

Continuous testing with IntelliJ Idea

I'm looking for an IntelliJ IDEA plugin that would run my tests each time I change my code. I looked for such a solution and I found:
Infinitest, which works, but is inconvenient because I need to add the facet to each module, and it opens a new tool window for each module (which means 15 tool windows for me).
Fireworks - didn't work for me, maybe it just doesn't work with IDEA 14 (in its repo I can see that last changes were made in 2009). IntelliJ also reports that it throws exceptions.
There are lots of ways I could run all my tests (including writing a simple script for this), but I'm looking for a tool that would be smart enough to rerun failed tests first, and that would understand module dependencies (so after a change in some module it would run only tests of dependent modules).
I prefer free options, but if there's something paid for a reasonable price, I would accept it as well.

IntelliJ now actually has a Toggle auto-testin the run dialog. Just run a run-configuration and then select Toggle auto-testin the run dialog.
It's not as intelligent as you would have hoped. It just reruns when it detects changes.

I know this is a 3-year-old question but I think it will help people who face the similar problem in future. So I found out a way to enable SBT style auto test execution in IntelliJ studio.
We need to do 2 things to enable auto test execution.
Enabling auto project build - This can be done in settings by going into File -> Settings -> Build, Execution... -> Compiler and selecting "Build Project automatically".
Enabling "Toggle auto-test" in run dialog box
This will start auto testing. Although this works fine, it takes time to build the project even when my project is tiny so for larger projects it will certainly take very long time to complete the build and execute tests.
Reference: Original article which explains these steps

If you are OK running tests which cover a single method chosen by you, you can try this plugin (it is continuos in the sense that you make changes to a method, then click on the method and the plugin will run all the unit tests automatically which cover that method): https://plugins.jetbrains.com/plugin/15063-unit-test-coverage-history-runner

You can use the Intellij Teamcity plugin. Teamcity is a paid product but there is a free version which gives you 20 projects and 3 agents for free .
It has a remote run feature using which you can send in unchecked code to run tests before committing.
It also has options to run failed tests first
Usage instructions for Remote Run

Creating a program that will run before and after compilation in Eclipse

I am currently working on a small program that should comment out some code used for testing.
I want it to auto run before the compiler while compiling the release version and another program that will comment the code back in after compilation was over.
The program works the only thing I am missing is to add it to the build process.
Thanks to all helpers!

In Eclipse, right-click a project, choose Properties → Builders and click New. You can add an Ant script or a command line that Eclipse will trigger when building the project. You can also control the order of builders in the same dialog.
However, I agree with JB Nizet – there are many advantages to having Ant or Maven build your project.

Don't use Eclipse to build the release version of your app. Use Ant, Maven, or any other build tool that is much more flexible than Eclipse, doesn't need a GUI, can be scripted and used by a continuous integration server.
All of these tools should easily be used to include your pre-compilation and post-compilation tasks in the build process.
That said, you could just use a public static final boolean constant FOR_TEST, and include all your testing code in
if (TestUtil.FOR_TEST) {
}
You would then have just a single place to change in the code to have all the test code removed from the compiled version. No need for a complex Java program to do that.
Or you could let all the testing code in the released version, and activate it when testing using a system property, for example. This wouldn't even need any precompilation/postcompilation phase, and would probably have a negligible cost.

Tool for creating Dynamically Generated Code in Java (In Eclipse)

In Visual Studio land, I used to be able to define a structure in an XSD file and add a special attribute to it which would cause it to be dynamically compiled and available to use with intellisense in the other C# files in the application. I am not sure exactly what the term for this is, perhaps "dynamic code generation."
I am trying to accomplish the same in Java using Eclipse IDE. Basically what I am looking for is a tool that will allow me to specify some template and generate Java code from it in a "hot folder" that will allow me code complete in the other static Java files.
Does anyone know of a solution for this? I know it is possible in Visual Studio, but I can't seem to find anything for Eclipse.
Ok, here is exactly what I want to do.
Step 1. I create a folder called templates
Step 2. I create a file called HelloWord.ibes
Step 3. Code it automatically generated in my src folder HelloWorld.java
I want to be able to do this in eclipse easily.

You may create an ant build file that does the source generation for you. Then you are free to use any code generator you like. Ant support is part of the eclipse IDE. If you prefer maven, there's a nice eclipse pluging available (that's what I actually use for source code generation based on jaxb, javacc and xdoclet...).
Technically spoken, you just add another eclipse builder which is invoked anytime eclipse detects a change in your code base.
If you already have a code generator in mind, just 'ask' the internet if there's a plugin available.
Edit
On how to install a builder: This is done automatically. For maven, you just install the maven plugin (m2eclipse) and enable maven dependencies for a project. Then if you look at the projects properties pages (Builder section), you find a second entry in the list of builders.
It's similiar with ant, even easier, because ant is already integrated. "enable" ant for a project and the builder is added to the list of builders for the project. You can deselect it at any time if it kills performance or switch of automatic building (I don't know by heart how to enable ant builds for a project, but I remember that the eclipse help had sufficiant informations).
All about ant can be found here: Apache Ant
Creating a new builder is difficult, as it has to be coded in java and added to eclipse as a plugin. I bet you don't want to follow that track ;)

I'm not sure whether you have seen the code template option?
Preferences.Java, Code Style then Code Templates
How
to add code templates
Useful
code templates