/* package whatever; // don't place package name! */
 
import java.util.*;
import java.lang.*;
import java.io.*;
 
/* Name of the class has to be "Main" only if the class is public. */
class Ideone
{
	public static void foo(List<List<Integer>> a)
	{
		a.add(new LinkedList<Integer>()); // putting a LinkedList where an ArrayList is expected!
	}
 
	public static void main (String[] args) throws java.lang.Exception
	{
		ArrayList<ArrayList<Integer>> a = new ArrayList<>();
		List cheat = a;
		foo(cheat);
		System.out.println(a.get(0)); // works!
		ArrayList<Integer> first = a.get(0); // nope!
	}
}

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