please explain

this question was from the final quiz. the correct answer was 16. I did not understand how the answer came.

public class Test
{
public static void leftshift(int i, int j)
{
 i<<j;
}
public static void main(String args[])
{
int i = 4, j = 2;
leftshift(i, j);
System.out.println(i);
}
}