strings.xml

<resources>
    <string name="app_name">androidtest2</string>
    <string name="size_s">S</string>
    <string name="size_m">M</string>
    <string name="size_l">L</string>
    <string name="size_xl">XL</string>
    <string name="size_xxl">XXL</string>
    <string name="size_xxxl">XXXL</string>
</resources>
 

Activity

size = getResources().getString(R.string.size_s);