Question

I’m wondering if final truly “freezes” its reference, forcing its underlying object to co-exist with any re-assignments made to the original reference via a different path e.g.

class ThingHolder{
    Thing thing;
}

class Thing{
    int i=5;
    Thing(int i){
        this.i=i;
    }
}

public static void main(String[] args){
    ThingHolder thingHolder = new ThingHolder();
    thingHolder.thing = new Thing(5);

    final Thing aFinalReference = thingHolder.thing;

    thingHolder.thing = new Thing(6); //will this now coexist with "aFinalReference"?

    //... 
}

Will aFinalReference now persist as in independent object, despite no longer being a part of thingHolder, and continue refering to the original Thing (i.e. the one whose int is currently 5), regardless of whatever now happens to thingHolder?

Answer 1

All that final really means here is that once you assign aFinalReference, you cannot reassign it.

To answer your question of what will reference what, we’ll just step through the code:

public static void main(String[] args){
    ThingHolder thingHolder = new ThingHolder();

    // create a new Thing (we'll call it "Thing5"),
    // and point thingHolder.thing at it

    thingHolder.thing = new Thing(5);

    // thingHolder.thing now points to Thing5

    final Thing aFinalReference = thingHolder.thing;

    // aFinalReference now ALSO points to Thing5

    // create a new Thing (we'll call it "Thing6"),
    // and point thingHolder.thing at it

    thingHolder.thing = new Thing(6);

    // thingHolder.thing now points at Thing6 instead of Thing5
    // aFinalReference, however, still points at Thing5
}

At the end of main():

• thingHolder.thing will point to “Thing6”
• aFinalReference will point to “Thing5”