How to prevent array data from being modified through a getter?

Question

Java

Hello. Help, please, to solve a problem. Given the code in which the array is changed through the getter. What are the ways to prevent such a change through a getter?

class two {
    private final List<Integer> array = new ArrayList();

    public final List<Integer> getArray() {
        return array;
    }


    @Override
    public String toString() {
        return "two{" +
                "array=" + array +
                '}';
    }
}

public class one {
    public static void main(String[] args) {
        two tw = new two();
        System.out.println(tw);
        tw.getArray().add(1);
        tw.getArray().add(2);
        tw.getArray().add(3);
        System.out.println(tw);

    }
}

Answer 1

It seems to me that in your case you need to look towards the Singleton pattern. For the return of the created copy, in my opinion, is still a crutch.

Answer 2

Collections.unmodifiableList(List);