Why should we use 'scan.nextLine();' before taking a string as an input?

Question

import java.util.Scanner;

public class Solution {

    public static void main(String[] args) {
            Scanner sc=new Scanner(System.in);
            int x=sc.nextInt();
            double y=sc.nextDouble();
            sc.nextLine();
            String s=sc.nextLine();


            System.out.println("String: "+s);
            System.out.println("Double: "+y);
            System.out.println("Int: "+x);
    }
}

the 's' variable could not take input of multiple words if I did not use sc.nextLine() before that. Can someone explain this?