Как эта программа на самом деле работает ...?

import java.util.Scanner;

class string
{
    public static void main(String a[]){
        int a;
        String s;
        Scanner scan = new Scanner(System.in);

        System.out.println("enter a no");
        a = scan.nextInt();
        System.out.println("no is ="+a);

        System.out.println("enter a string");
        s = scan.nextLine();
        System.out.println("string is="+s);
    }
}

Выход:

enter the no
1234
no is 1234
enter a string
string is=         //why is it not allowing me to enter a string here?