How Does Scanner Goes Through String Which Is Passed To It As Parameter

How does the Scanner goes through the String which is passed to it as a parameter. For example, String input = "222 dddd 222 ddd22" is passed to the method and here's the code:

Java Code:

public static void sum(String anything)
{
Scanner input = new Scanner(anything)
while(input.hasNext())
{
if(input.hasNextDouble())
{
double nextNumber = inut.nextDouble();
sum += nextNumber
}
......
......
} mh_sh_highlight_all('java');
{

So, how does Scanner calculates a passed String? I just want to know the way it calculates/reads.