How to add an item to an XML string-array from Java and then save it?

I have an XML file that is as follows:

<string-array name="Cube_type_entries">
    <item>2x2x2</item>
    <item>3x3x3</item>
    <item>4x4x4</item>
    <item>5x5x5</item>
    <item>6x6x6</item>
    <item>7x7x7</item>
    <item>8x8x8</item>
    <item>9x9x9</item>
    <item>Pyraminx</item>
    <item>Megaminx</item>
    <item>Clock</item>
</string-array>
<string-array name="Cube_type_values">
    <item>x2</item>
    <item>x3</item>
    <item>x4</item>
    <item>x5</item>
    <item>x6</item>
    <item>x7</item>
    <item>x8</item>
    <item>x9</item>
    <item>Pyraminx</item>
    <item>Megaminx</item>
    <item>Clock</item>
</string-array>

(It has the resource tag, and the other stuff needed)

And, I would like to add an item to Cube_type_entries, so a user could customize what he would like in it. So, the user hits an Enter button, I have the code for that, but I do not know how to insert it into the string-array then save it. (I am not looking for a dynamic one, I simply want it to be able to save it to the table every now and then)

So, how do I add to an XML string-array and then save it in Java?