Java Local reference over instance variable

Question

While going through the libgdx source code for a Stage, I encountered this segment:

public void draw () {
    Camera camera = viewport.getCamera();
    camera.update();

    if (!root.isVisible()) return;

    Batch batch = this.batch;
    if (batch != null) {
        batch.setProjectionMatrix(camera.combined);
        batch.begin();
        root.draw(batch, 1);
        batch.end();
    }

    if (debug) drawDebug();
}

(Link on GitHub.)

What interested me was this line: Batch batch = this.batch;

My first guess was some caching improvement. Am I right, or is there another reason to avoid using the instance variable directly?

Answer 1

In the early Java days, this was imho sometimes used as an optimization, to avoid accessing a member variable. However nowadays I believe, Hotspot can optimize better than us humans.

However, in this context it might be used to prevent problems in case of concurrent modification of that variable, since begin() and end() are likely required to be called on the same instance.