Flattening a string array

ArrayFlattener.java

public class ArrayFlattener {

    /**
     *
     * @param array containing objects of type String and/or array
     * @return
     */
    public static String [] flattenArray(Object [] array)
    {
        ArrayList<String> result = new ArrayList<String>();

        extractInto(result,array);

        //we need this to return an array of the correct type.
        String [] strTemplate = new String[1];
        return result.toArray(strTemplate);
    }


    /**
     *  Recursive function that adds all strings found to the destina
     * @param destination ArrayList of strings - will be appended to
     * @param array Containing Strings and arrays to extract
     */
    private static void extractInto(ArrayList<String> destination, Object [] array)
    {
        for(Object o:array)
        {
            if(o instanceof String)
                destination.add((String)o);
            else if(o instanceof Object[])
                extractInto(destination,(Object[])o);
        }
    }

}

ArrayFlattenerUnitTest.java

public class ArrayFlattenerUnitTest {


    final int SIZEOFARRAY = 18;
    
    @Test
    public void testComplexSolution()
    {
        //create a multilevel array hierarchy with number strings in order

        Object [] array = {new Object[]{"0"},"1",new Object[] {"2","3"},"4",new Object[] {new Object[] {"5"},new Object []{new Object[] {"6"},"7",new Object[] {"8","9"}},"10"},"11",
        new Object[] {new Object[] {new Object[]{"12","13",new Object[] {"14"}},new Object[] {"15", new Object[]{"16","17"}}}} };
        

        Object [] result = ArrayFlattener.flattenArray(array);

        //the result should be the number strings in order
        for (int i=0; i<SIZEOFARRAY; i++)
        {
            Assert.assertEquals(String.valueOf(i), result[i]);
        }

        //code coverage of this test is 100%!
    }
    

}