New to Java

I get this terrible error "StringIndexOutOfBoundsException string " when I run my code which successfully compiled and wonder how to fix it:

import  java.util.Scanner;       // Scanner Class for keyboard input
import java.text.DecimalFormat;  // Needed for DecimalFormat


public class assignment3Q1

{ //Start assignment3Q1 class


	public static void main(String[] args)
	{
		//Declare constants & variables
		int 	selling_price;
		char 	property_code;
		double 	commission,
				total_property_sales,
				total_commissions;
		String 	input;
		char 	more;

		total_property_sales = 0.0;
		total_commissions = 0.0;

		// Create a Scanner object
		Scanner keyboard = new Scanner(System.in);

		// Print header
		System.out.println("Deborah Michaliszyn \n" +
							"\n\nReal Estate Commission Calculator");
		do
		{

			//Get user's property selling price input.
			System.out.print("Enter the property selling price: ");
			selling_price = keyboard.nextInt();

			// check if sales_price is a negative value
			while (selling_price<0)
			{
				System.out.println("Enter : you must enter a positive value /n" +
								   "for selling price, Try again: ");
				selling_price = keyboard.nextInt();
			}

			// Enter the property code
			 System.out.println(
				"Enter the property code according to the following : \n" +
				"Residential		enter R \n " +
				"Multi-Dwelling		enter M \n " +
				"Commercial			enter C \n\n" +
				"Choose your code: ");

				property_code = keyboard.nextLine().trim().toUpperCase().charAt(0);
			while(property_code != 'R' && property_code != 'M' && property_code != 'C' )
			{
				System.out.println("Code must be an R, M, or a C!\n\n Choose your code: ");
			    property_code = keyboard.nextLine().trim().toUpperCase().charAt(0);
			}
			commission= calcCommission(property_code, selling_price);

		// Display the commission.
			System.out.println("the commission is :" + commission);

			total_property_sales += selling_price;   // Adds up total property sales.
			total_commissions += commission;   // Adds up commissions.

			//ask user if they want more commissions

			System.out.print("More Commissions? Y/N :");

			input = keyboard.nextLine(); //reads a line
			more = input.charAt(0); //get the first character

		}while (more == 'Y' || more == 'y');


		// Display the results.
		  System.out.println("Total Property sales: " + total_property_sales + " Total commissions " +
                              total_commissions);

	}//end main

	// call calcCommision method with arguments
	public static double calcCommission(char property_code, int selling_price)
	{
		final double	RESIDENTIAL_RATE = 0.07,
						MULTI_DWELLING_RATE = 0.06,
						COMMERCIAL_RATE = 0.035;
		double 			commission_rate= 0;


		System.out.println("Choose your code : \n");
		switch (property_code)
		{
			case 'R':	commission_rate = RESIDENTIAL_RATE; break;

			case 'M':	commission_rate = MULTI_DWELLING_RATE ;break;

			case 'C':	commission_rate = COMMERCIAL_RATE;

		}

		//calculate commision rate
		return	selling_price * commission_rate;

	}//end calcCommission

}