What is required to safely execute a compound operation, such as checking if an ArrayList is empty before accessing an element, when the list is shared among multiple threads?

import java.util.ArrayList;

public class CompoundAction {
    static ArrayList<Integer> list = new ArrayList<>();
    public static void main(String[] args) throws InterruptedException {
        Thread t1 = new Thread(() -> {
            synchronized(list) {
                if (!list.isEmpty()) {
                    list.remove(0);
                }
            }
        });
        Thread t2 = new Thread(() -> {
            synchronized(list) {
                if (!list.isEmpty()) {
                    System.out.println(list.get(0));
                }
            }
        });
        t1.start();
        t2.start();
    }
}