/* 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 main (String[] args) throws java.lang.Exception
	{
		List<List<Integer>> list = new ArrayList<>();
		list.add(Arrays.asList(1,2));
		list.add(Arrays.asList(3));
 
		int[][] arr = list.stream()
		    .map(l -> l.stream().mapToInt(Integer::intValue).toArray())
		    .toArray(int[][]::new);
 
		Arrays.stream(arr).forEach(a -> Arrays.stream(a).forEach(System.out::println));
	}
}

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