If you have a HiDPI high resolution screen i.e. lots of pixels but screen is physically small e.g. my new laptop has 3840x2400 pixels on a 13' screen, then the graphical tools for Tango will be displayed very small with excruciatingly small fonts which is not very useful. This is because the Tango Java graphical tools specify the font sizes in pixels but the pixels are physically very small now. There is a workaround for this using the environment variable GDK_SCALE.

Add this line to the jive startup script before starting java:
export GDK_SCALE=2

Increase GDK_SCALE to 4 or more if you want java applications to appear even bigger.

Tested on Ubuntu 20.04 with OpenJDK 11 but should work on most operating systems. Does not work on OpenJDK 8.

Thanks to @jlpons for finding the solution!
Edited 1 month ago