如何实现双ArrayList的可打包？

import java.util.ArrayList;
import java.util.List;

public class DoubleArrayListPackage<T> {
    private List<T> list1;
    private List<T> list2;

    public DoubleArrayListPackage() {
        list1 = new ArrayList<>();
        list2 = new ArrayList<>();
    }

    public void addToList1(T item) {
        list1.add(item);
    }

    public void addToList2(T item) {
        list2.add(item);
    }

    public List<T> getList1() {
        return list1;
    }

    public List<T> getList2() {
        return list2;
    }

    public List<List<T>> getPackage() {
        List<List<T>> packageList = new ArrayList<>();
        packageList.add(list1);
        packageList.add(list2);
        return packageList;
    }
}

DoubleArrayListPackage<String> doubleArrayListPackage = new DoubleArrayListPackage<>();
doubleArrayListPackage.addToList1("Item 1");
doubleArrayListPackage.addToList1("Item 2");
doubleArrayListPackage.addToList2("Item 3");
doubleArrayListPackage.addToList2("Item 4");

List<List<String>> packageList = doubleArrayListPackage.getPackage();
System.out.println(packageList.get(0)); // 输出: [Item 1, Item 2]
System.out.println(packageList.get(1)); // 输出: [Item 3, Item 4]