CommandLineCalculator-MostRobust

// MOST ROBUST IMPLEMENTATION IN THIS CHAPTER

import java.io.*;
import java.util.*;

/**
 * Performs addition from the command line on multiple accounts.
 *
 * Known issue: See known issues for indivudual methods
 */

class CommandLineCalculator
{
    private int accumulatedValue = 0;   // affected by arithmetic operation(s) on this

    // The accounts active in this session: Each object will be a 'CommandLineCalculator' instance
    private static Vector calculators = new Vector();

/*************************************************************************
 */
public CommandLineCalculator()
/*************************************************************************/
{   super();
}

/*************************************************************************
 * Intent: Performs addition of amounts enterd by the user to 'this'
 *
 * Precondition: 'CommandLineCalculator.calculators' != null
 *
 * Postconditions:
 * (1) The user has been prompted to add a sequence of integers or "stop" to quit this function
 * (2) The console displays each integer added as requested and the accumulating total
 * (3) The application has ended after the user has entered "stop"
 * (4) 'accumulatedValue' contains the total of all integers entered since the application began
 * (5) The console displays "Please enter an integer only." whenever the user has
 *     entered a non-integer, and allowed re-entry.
 *
 * Known issue: No provision for overflow
 */
protected void executeAdditions()
/*************************************************************************/
{
    // Get amount to add
    System.out.println
     ( "\tPlease enter the amount you want added, or type 'stop' to stop adding for now: " );
    String userRequest = getAnInputFromUser();

    // Add the amount if valid until "stop" entered
    int amountAdded = 0;
    while( !userRequest.equals( "stop" ) )
    {
        try   // -- to add the amount entered
        {
            amountAdded = ( new Integer( userRequest ) ).intValue();   // exception if not an integer
            this.accumulatedValue += amountAdded;
            System.out.println
             ( "\tAdded " + amountAdded + ", getting total of " + this.accumulatedValue );
        }
        catch( Exception e )   // non-integer entered
        {   System.out.println( "\tSorry -- incorrect entry: Try again." );
        }

        System.out.println
         ( "\tPlease enter the amount you want added, or type 'stop' to stop adding for now: " );
        userRequest = getAnInputFromUser();
    }

    System.out.println( "\tAddition ends." );

}   // end executeAdditions()

/*************************************************************************
 * Postcondition: the user has been prompted at the console for a string
 *
 * Return: String input by user if the user provides one, otherwise one blank
 */
private static String getAnInputFromUser()
/*************************************************************************/
{
    try
    {   BufferedReader b = new BufferedReader( new InputStreamReader( System.in ) );
        return ( b.readLine() );
    }
    catch( IOException e )
    {   System.out.println( e + " Input taken to be a single blank." );
        return " ";
    }

}   // end getAnInputFromUser()

/*************************************************************************
 * Intent: Get account from user and allow additions to and subtractions from it.
 *
 * Precondition: 'CommandLineCalculator.calculators' != null
 *
 * Postconditions:
 * (1) Application has prompted user repeatedly for an account in 'calculators' until
 * an existing account number is entered, and reported the balance on the account
 * (2) Application has ignored all inputs that make no sense and output explanation
 * (3) For each account chosen, the postconditions of 'executeAdditions()' apply
 * (4) User has entered "Quit application" and this method has terminated
 *
 * Known issue: The name of this method should be more precise.
 */
public static void interactWithUser()
/*************************************************************************/
{
    System.out.println
     ( "\n---------- Please enter account number between 1 and "  + calculators.size() +
         " or type 'Quit application': -----------" );
    String userRequest = getAnInputFromUser();

    int accountNum = 0;   // account currently requested
    while( !userRequest.equals( "Quit application" ) )   // return if "Quit ...."
    {
        try
        {   // This should be an integer -- if not, handle exception below
            accountNum = ( new Integer( userRequest ) ).intValue() - 1;

            if( accountNum >= 0 && accountNum < calculators.size() )   // account number within range
            {
                CommandLineCalculator cLC =   // get the account
                 (CommandLineCalculator)( CommandLineCalculator.calculators.get( accountNum ) );
                // Report on balance
                System.out.println
                 ( "\tThe balance in this account is " + cLC.accumulatedValue + "\n");
                cLC.executeAdditions();   // make the additions
            }
            else   // account number out of range
                System.out.println( "Please enter a legal account number." );
        }
        catch( Exception e )
        {   System.out.println( "Please enter an integer for an account number: Try again." );
        }

        // Repeat solicitation for account number
        System.out.println
         ( "\n---------- Please enter account number between 1 and "  + calculators.size() +
         " or type 'Quit application': -----------" );
        userRequest = getAnInputFromUser();
    }

}   // end interactWithUser()

/*************************************************************************
 *
 * Postconditions: As specified in the requirements document for "Command Line Calculator"
 */
public static void main( String[] args )
/*************************************************************************/
{
    solicitNumberAccounts();
    interactWithUser();
    System.out.println( "\n\t\t================ Application ends. ================" );

}   // end main()

/*************************************************************************
 * Precondition: 'CommandLineCalculator.calculators' not null, and has no elements.
 *
 * Postconditions:
 *  (1) The application has prompted the user for the number of required accounts until the user has
 * complied properly.
 *  (2) 'CommandLineCalculator.calculators' contains one 'CommandLineCalculator' object
 *      for each desired account, each initialized to zero.
 *
 * Known issue: No check on numer of accounts less than 0 or greater than overflow
 */
private static void solicitNumberAccounts()
/*************************************************************************/
{
    int numAccounts = 0;

    // Get the number of accounts
    System.out.println
     ( "\n================== How many accounts do you want to open: ==================" );
    try
    {
        numAccounts = ( new Integer( getAnInputFromUser() ) ).intValue();   // repeat if not integer

        if( numAccounts > 0 )   // legitimate number of accounts
        {
            System.out.println( "The application will deal with " + numAccounts + " accounts.\n" );

            // Establish the accounts
            for( int accountIndex = 0; accountIndex < numAccounts; ++accountIndex )
            {   CommandLineCalculator.calculators.addElement( new CommandLineCalculator() );
            }
        }
        else   // not legitimate number of accounts
        {
            System.out.println( "Please type a positive integer" );
            CommandLineCalculator.solicitNumberAccounts();   // try again
        }
    }
    catch( NumberFormatException e )
    {
        System.out.println( "Sorry, not an integer: Try again." );
        solicitNumberAccounts();   // repeat solicitation
    }

}   // end solicitNumberAccounts()

}