Qunand est ce qu'il faut vider le buffer (Memoire tampon)

/**
 * Addition,Multiplication,Division entière et Modulo en base quelconque
 */

package Algebre;
import java.util.Scanner;
public class Operations 
{
 static Scanner sc=new Scanner(System.in);
 static String val="0123456789ABCDEF";
 static int base;
 
 public static void main(String args[])
 {
     afficher();
 }
 
  public static void afficher()
 {
     String n1,n2;
     StringBuilder resultat;
     int operation;
     char op[]={'+','*','/','%'};
     
     readBase(); // choix de la base
     
     n1=readValue("premier");
     operation=operation();
     n2=readValue("deuxieme");
     
     resultat=calcul(toTen(n1),toTen(n2),operation);
     
     System.out.println(n1+" "+op[operation-1]+" "+n2+" = "+ resultat);
     
     sc.close();
 }
 
  public static StringBuilder toBase(int n)
 {
     StringBuilder  result=new StringBuilder();
     do
     {
         result.append(n%base);
         n/=base;        
     }while(n!=0);
     
     return result.reverse();
 }
  
 public static int toTen(String chaine)
 {
     int valeur,i=1;
     valeur=val.indexOf(chaine.charAt(0));
     
     while(i<chaine.length())
         valeur+=base*valeur+val.indexOf(chaine.charAt(i++));
         
    return valeur;
 }
 
 public static boolean checkValue(String valeur)
 {
     int i=0;
     String message;
     message=valeur+"ne peut être en base "+base;
     
     if(!valeur.matches("[0-9A-Z]+"))
     {
         System.out.println(message);
         return false;
     }
     while(i<valeur.length())
         if(val.indexOf(valeur.charAt(i))>=base)
            {
                System.out.println(message);
                return false;
            }
     return true;
 }
 
 
 public static void readBase()
 {    
     boolean faux=false;
    do
    {
        if(faux)
            System.out.println("Choisir une base valide");
        System.out.println("Préciser la base");
        base=sc.nextInt();
    } while(faux=base<2 || base>16);
     
 }
 
 public static String readValue(String name)
 {
     String terme=new String();
     sc.nextLine();
     do
     {
        System.out.println("Entrer le "+name+" terme");
        terme=sc.nextLine();
        
     } while(!checkValue(terme));
     
     sc.nextLine();
     return terme;
 }
 
 public static int operation()
 {
     int op;
     
    do
    {
         System.out.println("Choisir une opération");
         
         System.out.println("1-> +");
         System.out.println("2-> *");
         System.out.println("3-> %");
         System.out.println("4-> /");
                
         op=sc.nextInt();
    } while(op<1 || op>4);
    
    sc.nextInt();
    return op;
 }
 
 public static StringBuilder calcul(int a,int b,int op)
 {    
     switch (op) {
         case 1:
             return toBase(a+b);
         case 2:
             return toBase(a+b);
         case 3:
             return toBase(a%b);
         default:
             return toBase(a/b);
     }
 }
 
}