Removing elements from array in java throws exception

Question

I'm quite new to java and I'm still trying to figuring out how arrays work here. The following code, which I thought would print "2":

   import java.util.ArrayList;

   public static void main(String[] args) {

      ArrayList<String> myArray = new ArrayList<String>();

      myArray.add("1");
      myArray.add("2");
      myArray.add("1");
      myArray.add("1");

      for (String s: myArray){
        if(s == "1")
          myArray.remove(s);
      }

      for (String s: myArray) {
         System.out.println(s);
      }
   }

Throws this exception when executing:

Exception in thread "main" java.util.ConcurrentModificationException
    at java.base/java.util.ArrayList$Itr.checkForComodification(ArrayList.java:1042)
    at java.base/java.util.ArrayList$Itr.next(ArrayList.java:996)
    at ex.main(ex.java:40)

As I said this might be a stupid question, but my unexperienced eyes just can't see what is happening here.

Thank you all in advance.