Addvilz

All aboveplus
 
Sanctuary
Expanse
Killjoys
Dark Matter
Farscape
Warehouse 13
Defiance
Orville
Firefly
Terra Nova
Fringe
 
... to name a few ?

No issue whatsoever doing that, as long as you mentally keep those languages boxed and don't force one to work like the other one. But I don't see why not.  

All aboveplus
 
Sanctuary
Expanse
Killjoys
Dark Matter
Farscape
Warehouse 13
Defiance
Orville
Firefly
Terra Nova
Fringe
 
... to name a few ?

Autocorrect and completion show you these kind of errors right away.

All aboveplus
 
Sanctuary
Expanse
Killjoys
Dark Matter
Farscape
Warehouse 13
Defiance
Orville
Firefly
Terra Nova
Fringe
 
... to name a few ?

This is what you are looking for:
public class Ring { // This is a field of Ring object private final double radius; // This is a contstructor public Ring(final double radius) { this.radius = radius; } // This is a method. Note the 'double' return type. public double getRadius() { return this.radius; } // This is also a method. Note the 'return' keyword. public double computeCir() { return 2 * Math.PI * this.radius; } } Watch for typos. Method names and variable names must match between definition and access. Java does not allow nested method definitions. To avoid confusion, I recommend referring to instance variables (fields) with "this." prefix.  Things that are not supposed to mutate should be marked immutable explicitly using 'final' keyword. Methods must have return types. Your code sample was using void in places. Void means "returns nothing". Return keyword is mandatory in Java. Also, try to write code incrementally while learning and avoid copy pasting - write small chunks, test if it works, repeat. Otherwise you end up with several unrelated issues that might be confusing to fix.
 
Working example: https://repl.it/repls/FatherlyFairAggregators

No, you really don't. All text editors with syntax highlighting support C/C++. It's just text. Just pick one that is most comfortable for you to use. And if you are seriously committed to this, you should eventually try CLion. It's not free, but it is damn well worth it. 

I did something similar quite a few years back, an Android native app that used to connect to a machine running "agent". The agent was basically a small Java application utilizing java.awt.Robot for controls.
 
Unfortunately, there is a pretty significant eventual downside to this - screen burn in. Screens have advanced since then, yet, I would not use this on a tablet that I would not consider disposable. 
 
But the idea has perspective, sure.