Java: How to make local fields & parameters final without having a ‘final’ keyword on each declaration

I use final the same way as you. To me it looks superfluous on local variables and method parameters, and it doesn't convey useful extra information.

One important thing is that strive to keep my methods short and clean, each doing a single task. Thus my local variables and parameters have a very limited scope, and are used only for a single purpose. This minimizes the chances of reassigning them inadvertently.

Moreover, as you surely know, final doesn't guarantee that you can't change the value/state of a (nonprimitive) variable. Only that you can't reassign the reference to that object once initialized. In other words, it works seamlessly only with variables of primitive or immutable types. Consider

final String s = "forever";
final int i = 1;
final Map<String, Integer> m = new HashMap<String, Integer>();

s = "never"; // compilation error!
i++; // compilation error!
m.put(s, i); // fine

This means that in many cases it still doesn't make it easier to understand what happens inside the code, and misunderstanding this may in fact cause subtle bugs which are hard to detect.

There's a simple way to do this: You set up an object with the synchronized data and share it between the threads. You can then write the data or check for it from each thread.

So, you'd have an instance of a class that looks like this:

public class Shared {
    private boolean signalSent = false;

    public synchronized boolean isSignalSent(){
        return this.signalSent;
    }

    public synchronized void setSignalSent(boolean signal){
       this.signalSent = signal;  
    }
}

You may want to consider, if the signal can be re-sent, to have a method that reads and resets the value.

In any case, the instance of that class should be passed to both threads, and will be able to do something like

if(!shared.isSignalSent()){
    // behave a certain way
} else {
    // behave another way
}