[java] Class JavaLaunchHelper is implemented in two places

Today I upgraded my Intellij Idea on macOS Sierra, and now, when I run apps in console I have this error:

objc[3648]: Class JavaLaunchHelper is implemented in both /Library/Java/JavaVirtualMachines/jdk1.8.0_121.jdk/Contents/Home/bin/java (0x10d19c4c0) and /Library/Java/JavaVirtualMachines/jdk1.8.0_121.jdk/Contents/Home/jre/lib/libinstrument.dylib (0x10ea194e0). One of the two will be used. Which one is undefined.

I am using Intellij Idea 2017 and I got into the same problem. What solved the problem for me was to simply

1. close the project in intelliJ
2. File -> New -> project from existing resources
3. use Import from external model (if any)
4. open the project again.

This was an issue for me years ago and I'd previously fixed it in Eclipse by excluding 1.7 from my projects, but it became an issue again for IntelliJ, which I recently installed. I fixed it by:

1. Uninstalling the JDK:

   cd /Library/Java/JavaVirtualMachines
   sudo rm -rf jdk1.8.0_45.jdk
   

   (I had jdk1.8.0_45.jdk installed; obviously you should uninstall whichever java version is listed in that folder. The offending files are located in that folder and should be deleted.)

2. Downloading and installing JDK 9.

Note that the next time you create a new project, or open an existing project, you will need to set the project SDK to point to the new JDK install. You also may still see this bug or have it creep back if you have JDK 1.7 installed in your JavaVirtualMachines folder (which is what I believe happened to me).

Since “this message is harmless”(see the @CrazyCoder's answer), a simple and safe workaround is that you can fold this buzzing message in console by IntelliJ IDEA settings:

1. ?Preferences?- ?Editor?-?General?-?Console?- ?Fold console lines that contain?
   Of course, you can use ?Find Action...?(cmd+shift+A on mac) and type Fold console lines that contain so as to navigate more effectively.
2. add Class JavaLaunchHelper is implemented in both

On my computer, It turns out: (LGTM :b )

And you can unfold the message to check it again:

PS:

As of October 2017, this issue is now resolved in jdk1.9/jdk1.8.152/jdk1.7.161
for more info, see the @muttonUp's answer)

I have found the other workaround: to exclude libinstrument.dylib from project path. To do so, go to the Preferences -> Build, Execution and Deployment -> Compiler -> Excludes -> + and here add file by the path in error message.

Same error, I upgrade my Junit and resolve it

org.junit.jupiter:junit-jupiter-api:5.0.0-M6

to

org.junit.jupiter:junit-jupiter-api:5.0.0

This happened to me when I installed Intellij IDEA 2017, go to menu Preferences -> Build, Execution, Deployment -> Debugger and disable the option: "Force Classic VM for JDK 1.3.x and earlier". This works to me.