Java Thread Synchronization and Visibility

In the provided code, a writer thread modifies a shared ArrayList while a reader thread accesses it. Which approach best ensures that the reader thread will observe the most recent list size?

import java.util.ArrayList;

public class VisibilityTest {
    static ArrayList<Integer> list = new ArrayList<>();
    public static void main(String[] args) throws InterruptedException {
        Thread writer = new Thread(() -> {
            for (int i = 0; i < 10; i++) {
                list.add(i);
                try { Thread.sleep(20); } catch (InterruptedException e) {}
            }
        });
        Thread reader = new Thread(() -> {
            try { Thread.sleep(50); } catch (InterruptedException e) {}
            System.out.println(list.size());
        });
        writer.start();
        reader.start();
        writer.join();
        reader.join();
    }
}