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.
Is it necessary to use the same ide to program in java? For example, I use IntelliJ to build a small java project about 2000 lines. Then the marker uses Eclipse IDE to mark this project. Does he need to import all the source code into a new project and set up everything for it? I didn't use any add-on on this IDE.
The reason I asked this question because I receive huge grade duction for using different IDE, the prof response me and said marker need rebuild everything for using different ide.
I drag my source code into Eclipse, and it works very well, so I am confused am I right or wrong?
Previously I used Eclipse, but now I am using Intellij IDEA. But I can't understand one thing. In Eclipse I have SETs in which I have a group of projects. At all I have a lot of different small projects to which I have simultaneous access and I see them all in the Package Explorer. In Intellij IDEA I see only one project, and this is not convenient for me.
Does Intellij IDEA have an analogue Package Explorer? How can I see many projects in one window?
I believe you cannot open multiple unrelated projects in one window like you do in Eclipse.
You'd need to open them in multiple windows, File > Open ... and you'll choose a new window. I also wished Intellij could open multiple projects in single window. But now I get used to it. Just click CMD + ` to switch between Intellij instances on OSX.
If they're modules of your project, then you can add them from File > New > Module From Existing sources...
OK, I have a really basic (read stupid) question. I am just beginning Java programming, and am using Eclipse 3.7.2. I have done a few beginning projects without any problems. All of a sudden, when I create a new project using the wizard, it is not creating the src/.java file. When I try to manually add it after creating the project, I end up getting some cryptic error messages.
I have re-followed several walk-throughs on project creation for clues as to any option I may have accidentally un-checked and no luck.
Googling the answer brings up results for more advanced problems that are unrelated.
I have combed the preferences, but nothing looks obvious, and
I have gone hunting for any user app data I could delete to force a clean slate.
I have even created a new instance of Eclipse to a different directory and still have the same result.
My son's instance, which is on the same computer still creates the .java file from the wizard. The only difference is that my instances have the Android SDK installed (I am trying to create basic Java projects and not Android projects).
I am at a loss, and have lost a lot of time trying to correct the situation. What do I need to do to reenable the creation of a src/.java file in Eclipse?
Screenshots (click on image for full size):
Make sure you are choosing a java project from the right folder in the wizard. It sounds like it is creating an android java project, which is probably why your src folder is missing. See if there is a helloworld project under example projects too in the wizard, that may get you started too. Screenshot may help us. I want to see which project type you choose and which folder it is in.
How about changing eclipse to point to a new workspace. That may drop the android settings. Under the file menu, choose switch workspace and pick a new location. Thats most likely why a new install did not fix it. That workspace may have android settings in it, so change to a new folder somewhere else to test it like c:\workspace2\
Here's a good tutorial I found that may help too.
eclipse java project tutorial
I have a problem now :
When I want to compile my project in Netbeans IDE I had this message error :
Problem: The project uses a class library called "toplink", but this class library was not found.
Solution: Click Resolve to open the Library Manager and create a new class library called "toplink".
In fact I didn't change anything and it works fine before?
What's the problem?
It seems that you have to import the library itself.
On the left pane in your Netbeans editor, you should have a series of panes. One of these is called the Projects pane. If you click on it, you should be able to see the files and packages which make up the project you are editing as nodes. One of these nodes, at the very end is called "Libraries". Right click on this node and select "Add Library". From there, you should be able to browse and locate the library.
I believe libraries are defined for the NetBeans installation rather than for the project. You can import a library into a project which would make it available on other NetBeans installations. Perhaps you are on a different computer or a new installation of NetBeans?