NetBeans GUI Builder from existing file

I am new to NetBeans IDE and I am using NetBeans GUI builder for creating my GUIs. I am creating a new file by right-clicking the package and click new and then click the new JFrame Form.

It is working fine. But I have a java file with a JFrame which I created manually by coding.

Can I import it into that GUI builder so that I can drag and drop and make the GUI? If yes How can I do that? (In eclipse we can do that by right-clicking the file and click open with windowbuilder editor.)

The Netbeans GUI builder works by generating code fully controlled by Netbeans, plus it maintains a hidden .form file. So you can't directly import your JFrame and make it fully customizable by the GUI Builder.

However there are things that might help.

You can modify your JFrame by adding JPanels designed using the GUI Builder. In Netbeans project view, select your package and create a new JPanel form, edit it, save it. Then in your JFrame code, manually insert JPanel instances where you need it.

Another trick:

• Extract the UI code from your JFrame and create a JPanel file with it, with a public no-argument constructor.
• Compile it
• Select the JPanel file in the Netbeans projet view, then righ-click Tools/Add to palette
• Add it to a Category (you can create your own category if needed)
• Create a new JFrame form from Netbeans
• You should see your JPanel component available in the GUI builder palette, in the relevant Category
• Drag & drop your JPanel component in the JFrame form

Note that the JPanel will not be editable itself, you can just manipulate it as a block in the GUI builder.

NOTE: in my experience, after doing Tools/Add to palette, it's sometimes needed to close/reload a form file to have the added component actually appear in the GUI builder palette.