Question

How can I use the same arraylist row to add values into the nested array tableValues since the clear command removes the data in row.

Thanks

    ArrayList<ArrayList<String>> tableValues = new ArrayList<ArrayList<String>>();
    ArrayList<String> row = new ArrayList<String>();

    row.add("a");
    row.add("b");
    row.add("c");
    tableValues.add(row);
    row.clear();

    row.add("d");
    row.add("e");
    row.add("f");
    tableValues.add(row);
    row.clear();

    row.add("g");
    row.add("h");
    row.add("i");
    tableValues.add(row);
    row.clear();

    System.out.println(tableValues);

Answer 1

I’m sure you really want to add three different ArrayLists, so change each row.clear() to:

row = new ArrayList<String>();

Why would you want to “use the same arraylist row to add values”? I can’t see why you’d want your top-level ArrayList to basically contain the same reference three times. Why would you not want them to be references to independent lists?