People are complaining about how bad SWT is, and I definitely agree. It's a product of systems engineers, not the modern hipster-designer breed of developers.
If you fall into the latter category and want to work with Java, I highly recommend JavaFX Webview. It's essentially webkit as a UI layer, so you get to work with HTML5/Bootstrap/whatever. Surprisingly, its interface from Java to Javascript is quite well designed.
Not to say everything else is perfect in JavaFX world but I think if you want to deploy a JavaFX application that is cross platform, the only major missing piece now is auto update support/framework for these self contained applications
If you fall into the latter category and want to work with Java, I highly recommend JavaFX Webview. It's essentially webkit as a UI layer, so you get to work with HTML5/Bootstrap/whatever. Surprisingly, its interface from Java to Javascript is quite well designed.