Many users have faced issues when running versions of Java that are either outdated, or are produced by organisations other than Oracle (e.g. OpenJDK). The errors generated by these issues will not always clearly point to the JDK as the cause. If in doubt, check your JDK version by following the instructions `here <https://java.com/en/download/help/version_manual.xml>`_. You can download the latest version of Oracle's JDK `here <http://www.oracle.com/technetwork/java/javase/downloads/index.html>`_.
JavaFX is not bundled with OpenJDK. If you are using OpenJDK and get an 'Unresolved reference: javafx' error, this means that you need to install OpenJFX.
If you have APT installed and OpenJFX is part of your Unix distribution's package list, you can do this by running ``sudo apt install openjfx``, and possibly ``sudo apt install libopenjfx-jav``. Other users will want to refer to the guide `here <https://wiki.openjdk.java.net/display/OpenJFX/Building+OpenJFX>`_, or to the list of Community Builds `here <https://wiki.openjdk.java.net/display/OpenJFX/Community+Builds>`_.
If still have problems, the JetBrains website has more information on `here <https://www.jetbrains.com/help/idea/2016.2/working-with-gradle-projects.html>`_.
If IDEA refuses to open a project because an SDK has not been selected, you may need to fix the project structure. Do this by following `these instructions <https://www.jetbrains.com/help/idea/2016.2/configuring-global-project-and-module-sdks.html>`_. The correct JDK is often found on a path such as ``jdk1.8.0_xx…/Contents/Home``. Ensure that you have the Project language level set at 8.
If you are having trouble selecting the correct JDK, the JetBrains website provides the `following guidelines <https://intellij-support.jetbrains.com/hc/en-us/articles/206544879-Selecting-the-JDK-version-the-IDE-will-run-under>`_.
First check that Corda compiles successfully from the command line using ``gradlew clean build``. If this succeeds then IntelliJ may just have imported the project's Gradle files incorrectly. Try opening the
..parsed-literal::
View/Tool Windows/Gradle
..
pane and clicking the "Refresh all Gradle projects" button. Then retry compiling Corda within IntelliJ. If this still fails then try
1. Via the initial project opening screen, by using the ``Configure > Plugins`` tab.
2. From an open IDEA project, by clicking ``IDEA -> Preferences ...`` (on OS X) or ``File -> Settings`` (on Windows). Select the Plugins bar to confirm that Kotlin is installed and up-to-date.
This can cause long delays with starting Corda nodes as every attempt to look up the name of the local computer triggers
a five second pause. This is not a bug in Corda but rather `a problem with the macOS networking stack <http://stackoverflow.com/questions/39636792/jvm-takes-a-long-time-to-resolve-ip-address-for-localhost>`_.
To fix it, you will need to use the Terminal app and edit your ``/etc/hosts`` file. For instance, you can do this by
typing:
``sudo nano /etc/hosts``
then typing in your own password, assuming you are an administrator user of the computer.
You will need to ensure there are two lines for the name of your machine (which you can find in the Sharing section
of System Preferences), which look like this:
..parsed-literal::
127.0.0.1 MacBook-Pro.local
fe80::1%lo0 MacBook-Pro.local
If you've changed the name of your computer in Sharing or via the ``hostname`` command, obviously ensure you replace
``MacBook-Pro.local`` with the correct name. Then press Ctrl-O to save the file and Ctrl-X to exit.
