What PL to use for cross-platform development in 2015?

Question

Java

It is necessary to write a cross-platform application for Linux (Ubuntu) and Windows 7 +
From the knowledge there is JS, PHP - actually a web developer. There is also experience in writing applications for Android in Java.
From what I tried:
NW.js is not bad, but the output of 100mb EXE for HelloWorld is depressing.
WinJS - only under Windows and only Metro. I wrote under WinPhone, I didn’t really like it, it worked much worse than in C # (in terms of speed)
Java - it’s not clear what to use here: there is Swing and SWT, but I don’t think it works fast + you need to drag JRE, but how much is there output will be unknown.
Most importantly:
easy customization of controls, if there would be html markup, it would be great.
So far I have settled on NW.js, but if there is something better, write.
I would also stop at Java, especially since I really like Java, but in terms of GUI, everything seems to be bad.
In advance, many thanks to everyone.

Answer 1

No
cross-platform out of the box - a myth

Answer 2

Pure cross-platform is a web application. The client does not care what your application is written on, the main thing is that it opened in the browser. For desktops, there is no perfect solution.

Answer 3

if you like java, then you can try javafx. There is a customization of controls in a css-like language. Here is a small tutorial on the feel of code.makery.ch/library/javafx-8-tutorial/en

Answer 4

If we are talking about mobile heresy, then JavaScript + ionic

Answer 5

c++, freepascal

Answer 6

If the application does not use system-specific functions and is not tied to some specific things, such as special equipment, feel free to take any cross-platform GUI framework that you like the most.
Well, out of habit, they will advise Qt + C ++, because I myself practice.

Answer 7

> you need to drag the JRE
Now it is divided into 3 profiles, the first occupies 15 Mb. In version 9, it will be possible to create your own jre distribution by putting only the necessary classes into it. Thus, you can meet less than 15 MB.