Simple solution:

1. String[] foo = { "3", "14", "15", "926" };
2. int[] fii = int(foo);
3. println(fii);
4. exit();

But apparently, you have more complex lines. You need to loop over the array of strings, split the string on whatever separator you have (your description is vague), and convert each part to int, to put it in your destination array.
Show some code, we might be able to help more.

I have the same problem this solution somehow does not work for me my code is like this.

        if (Fruit[2].equals("Appel") == true)
        {
          Shake[3] = Shake[3] + Vitamines[2] ;
          println(Shake[3]);
        }

The output should be a int value. I get cannot convert String to int.
(not all array values in the array vitamines are int by the way.)

" not all array values in the array vitamines are int by the way"
That's not logical. In Java, all items in an array have the same type.
Perhaps you mean that Vitamines is an array of strings, some of them representing integers (like "12").
In this case, if Shake is a an array of ints, the message is logical.
You can try: Shake[3] += int(Vitamines[2]);