Product tested:JDK 8b231b01(64bit)
OS/architecture:Ubuntu 19.04 x64
Option:-Dswing.defaultlaf=com.sun.java.swing.plaf.gtk.GTKLookAndFeel -Djdk.gtk.version=3 -Djdk.gtk.verbose=true

Reproducible: Always
Reproducible on blr003a113.in.oracle.com
Is it a Regression:Yes
There is significant difference between what is rendered on GTK3 as compared to the the rendering using GTK2.

To reproduce, run the attached Test FlowLayoutTest.java with the options specified above.
Run the same test with the gtk version set to 2 as well to compare against the expected behavior.

The focus border overlaps over the text present in the JTextfied as well as the cell in the JTable.
No such issue seen when the test is run with GTK2.

Images attached:
GTK3FocusBorderJTable.png, GTK3FocusBorderJTextField.png
The above show the gtk3 behavior when the focus is on the corresponding component.
GTK2FocusBorderJTable.png, GTK2FocusBorderJTextField.png
The above show the gtk2 behavior when the focus is on the corresponding component. The border is either not present or it is at the boundary of the component thereby making it not overlap with the text of the component.