a = [1, 2, 3]
b = a
b.append(4)
print(a) # 👉 [1, 2, 3, 4]
print(b) # 👉 [1, 2, 3, 4]
print(a is b) # 👉 True
List<Integer> a = new ArrayList<>(List.of(1, 2, 3));
List<Integer> b = a;
b.add(4);
System.out.println(a); // 👉 [1, 2, 3, 4]
System.out.println(b); // 👉 [1, 2, 3, 4]