Since the method is named insertEvil, the point of this exercise is probably to teach you that it is possible to insert the "wrong" type of object to a ArrayList<T>, and that generics are not actually enforced at runtime. See: type erasure.
In this case, you need to insert a String into a ArrayList<Integer>.
One way to do it is to cast it to a raw type:
((ArrayList)intList).add("Hello World");
However, this doesn't actually cause your code to print "OK", because the call to intList.get would attempt to cast the string you inserted back to an Integer, because intList is declared to be an ArrayList<Integer>. The cast will fail at runtime.
To get this to work, you need intList to be a ArrayList or ArrayList<String>, so the call to get wouldn't try to cast the string to Integer.
If you are only allowed to change the code between the two comments, the only ways I can think of are dirty tricks like declaring a new method. You can still declare a new method by just changing the lines between the two comments.
For example, if the code between the two comments are replaced with:
helper(intList);
}
static void helper(ArrayList intList) {
intList.add("Hello World");
Then it becomes:
static void insertEvil() {
var intList = new ArrayList<Integer>();
// Change starts here
helper(intList);
}
static void helper(ArrayList intList) {
intList.add("Hello World");
// Change ends here
if (intList.get(0).equals("Hello World")) {
System.out.println("Ok");
} else {
System.out.println("Failure");
}
}
The idea is to pass intList to another method, to change what intList means in the get call. In the above code, intList in the get call now refers to the method parameter, instead of the variable declared in insertEvil.
That said, I think it is highly likely that the intended solution is just ((ArrayList)intList).add("Hello World");. Whoever designed this might not have considered that get would cast the element back to an Integer. (I nearly missed it too!)
