You can do an enhanced for loop (for java 5 and higher) for iteration on array's elements:

String[] elements = {"a", "a", "a", "a"};   
for (String s: elements) {           
    //Do your stuff here
    System.out.println(s); 
}

Since atleast Java 1.5.0 (Java 5) the code can be cleaned up a bit. Arrays and anything that implements Iterator (e.g. Collections) can be looped as such:

public static boolean inArray(int[] array, int check) {
   for (int o : array){
      if (o == check) {
         return true;
      }
   }
   return false;
}

In Java 8 you can also do something like:

// import java.util.stream.IntStream;

public static boolean inArray(int[] array, int check) {
   return IntStream.of(array).anyMatch(val -> val == check);
}

Although converting to a stream for this is probably overkill.

Found the answer

public class App {
    public static void main(String[] args) throws Exception {
        Car car = new Car();
        Bicycle bicycle = new Bicycle();
        Van van = new Van();

        Object[] racers = {car, bicycle, van};  

        for(Object x : racers) {
            System.out.println(x.getClass()); 

            ((Vehicle) x).go();  // this is the only change I made
        }
    }
}

The better question might be: Why wouldn't you want to use a FOR loop to iterate through an array? There are many ways to iterate through an Array or a collection and there is no law that states you have to use the FOR loop. In a lot of cases, it's simply the best to use for speed, ease of use, and readability. And yet, in other cases it is not:

The Array:

int[] array = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10};

Display Array with the typical for loop:

for (int i = 0; i < array.length; i++) {
    System.out.println(array[i]);
}

Display Array with the enhanced for loop:

for(Integer num : array) {
    System.out.println(num);
}

Display Array with the do/while loop:

int i = 0;
do {
    System.out.println(array[i++]);
} while (i < array.length);

Display Array with the while loop:

int j = 0;
while (j < array.length) {
    System.out.println(array[j++]);
}

Display Array through Recursive Iteration:

iterateArray(array, 0);  // 0 is the start index.


// The 'iterateArray()' method:
private static int iterateArray(int[] array, int index) {
    System.out.println(array[index]);
    index++; 
    if (index == array.length) {
        return 0;
    }
    return iterateArray(array,index);
}

Display Array using Arrays.stream() (Java8+):

Arrays.stream(array).forEach(e->System.out.print(e + System.lineSeparator())); 

Display Array using IntStream (Java8+):

IntStream.range(0, array.length).mapToObj(index -> array[index]).forEach(System.out::println);

Choose your desired weapon....