If you use Eclipse IDE for Java development, you will find that there is a great GUI builder from Google, and it worked very well on previous releases of Ubuntu.
Unfortunately, Eclipse just freezes when you use Windows Builder on 64 bit Ubuntu 14.04 LTS. Several posts on the Internet suggest installing Oracle Java 7 32 bit and Eclipse IDE 32 bit, stating that Windows Builder will only work with that architecture.
In my case, I used Oracle Java 7 64 bit and Eclipse IDE 64 bit and had this issue. To overcome, I removed Oracle Java 7 and installed Oracle Java 8. To do so, open a terminal window and enter the following commands:
sudo apt-get purge oracle-java7-installer <enter>
sudo apt-get install oracle-java8-installer <enter>
With Oracle Java 8 64 bit, Windows Builder Pro works perfectly fine.