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I am currently completely stuck with the following problem: I want an GUI with a cotrol panel at the right to type in some program parameters that should be used to draw multiple lines onto a graphic panel at the left side of my GUI. My approach was to use the Form Designer to arrange the Layout with all the Buttons, Lables and TextFields. Than I created a Class "GraphicPanel" that extends JPanel and I overrided the PaintComponent method of this class in order to draw the lines.

Now I want to add this custom created component via the form Designer to my UI. But when I try this via the Non-Palette-Component option: nothing happens and the component is not even shown in the hierarchy-tree. I have already serached the web for solutions and found that my class needs to be compiled and the ReloadCustomComponents-Button must be clicked after inserting custom stuff. My class is compiled but the ReloadCustomComponents-Button is not shown up in the UI-Designer Toolbar. I tried to configure the toolbar manually - and in the configuration setup Intellij is also listing the Button as a displayed icon - but it is not there when I apply the configuration. Did anyone had the same problem or does anyone have any suggestions what I can try or what else I can check out? I am actually wondering if this is a software bug or whether I missed something different. I am quite a beginner and especially working with UI's and Swing is new for me so I have no real idea how to go on with this. Thanks for any help!

(I am using Intellij Idea 2020.3.1 on Windows and JDK 15.0.1 and my output format for the UI-form code is set to binary class files)

Logicalfrog
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    Try setting the language level of the project to 11. See https://stackoverflow.com/a/12900859/104891 for the relevant configuration screenshots. If you compile your class for JDK 15 IntelliJ IDEA will not be able to load it as it runs under JDK 11. – CrazyCoder Jan 20 '21 at 18:37
  • Thanks a lot! That solved my problem indeed... – Logicalfrog Jan 26 '21 at 12:25

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UI component classes used in the UI Designer palette must be compiled for the same or lower Java target version as is used to run IntelliJ IDEA. IDE JDK version is available in Help | About dialog and is 11 for 2020.x IDE versions.

Change the target JDK version to 11 so that IDE can load the component classes. See this answer for the relevant places where JDK language levels are configured.

CrazyCoder
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