Principale

package calcolatrice;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class Principale {

    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        InputStreamReader isr=new InputStreamReader(System.in);
        BufferedReader br=new BufferedReader(isr);
        System.out.println("Inserisici il tuo calcolo");
        try {
            String s=br.readLine();
            Calcolatrice c = new Calcolatrice(s);
            System.out.println(c.risultato());
        } catch (IOException ex) {
            System.err.println(ex);
        } catch(java.lang.NumberFormatException ex){
            System.err.println(ex);
        }
    }
}