What is the result of compilation and execution of

What is the result of compilation and execution of the following program:


import java.util.*;

class Main {
    public static void main(String[] args) {
        List<?> list = new ArrayList<String>();
        list.add("a");
        System.out.println(list.get(0));
    }
}

Runtime exception
It will print out "a"
It will not print anything
Compilation error

Explanation

When you have an object of generic class defined with a wildcard <?>, you can't call methods, that take arguments of type-parameter. The only exception from this rule is passing the value null.