Question

Using Java

Write a simple calculator which can add, subtract, multiply, and divide. Here are the specifications for the calculator:

• The calculator has one “accumulator”, which holds the result of all prior calculations. The calculator is set to 0.0 when the calculator is turned on (i.e., instantiated).
• On the console, the user then enters an operator (+, -, *, or /) and a number. Your console will then apply the operator and operand to the number in the accumulator, and store the result back in the accumulator
• The user can also enter ‘R’ to reset the accumulator to 0, or the letter “P” to turn the calculator’s power off

The calculator will need to trap the following exception conditions:

• If the user enters something other than +, -, *, /, R, or P for the operator, an UnknownOperatorException exception should be thrown.
• If the user enters something other than a valid number for the operand, a NumberFormatException exception should be thrown. (You can ignore this exception if the user enters R or P for the operator.)
• If the user tries to divide by zero, an DivideByZeroException exception should be thrown.

The NumberFormatException is already provided in Java. You will write your own UnknownOperatorException and DivideByZeroException classes.

All exception classes should have at least two constructors:

• one which takes no arguments and provides a default Exception message
• another which takes a String as an argument and sets the contents of the String as the Exception message

Please provide listings for your Calculator class (or classes) and your exception class. Also provide a PrintScreen(s) demonstrating each of the six operators and three exceptions in use.

Here’s a sample dialog that a user might have with the calculator:

Your calculator is now on. The result is currently 0.0 Enter an operator (+, -, *, or /) and a number, "R" to reset, or "P" to turn off power + 5 The result of 0.0 + 5.0 is 5.0 Enter an operator (+, -, *, or /) and a number, "R" to reset, or "P" to turn off power / 2 The result of 5.0 / 2.0 is 2.5 Enter an operator (+, -, *, or /) and a number, "R" to reset, or "P" to turn off power / 0 You cannot divide by 0. The result is still 2.5. Enter an operator (+, -, *, or /) and a number, "R" to reset, or "P" to turn off power R The calculator has been reset to 0. Enter an operator (+, -, *, or /) and a number, "R" to reset, or "P" to turn off power – 18.4 The result of 0.0 - 18.4 is -18.4 Enter an operator (+, -, *, or /) and a number, "R" to reset, or "P" to turn off power * 20 The result of -18.4 * 20.0 is -368.0 Enter an operator (+, -, *, or /) and a number, "R" to reset, or "P" to turn off power + abc "abc" is not a valid number. The result is still -360.0 Enter an operator (+, -, *, or /) and a number, "R" to reset, or "P" to turn off power & 15 "&" is not a valid operator. The result is still -368.0 Enter an operator (+, -, *, or /) and a number, "R" to reset, or "P" to turn off power P Good bye.

Answer 1

//Java code

public class UnknownOperatorException extends Exception {
    public UnknownOperatorException()
    {
        super();
    }
    public UnknownOperatorException(String msg)
    {
        super(msg);
    }
}

//===============================

public class DivideByZeroException extends Exception {
    public DivideByZeroException()
    {
        super();
    }
    public DivideByZeroException(String msg)
    {
        super(msg);
    }
}

//===============================

import java.util.Scanner;

public class Calculator {
    public static void main(String[] args) throws UnknownOperatorException {
        String expression ="";
        Scanner input  = new Scanner(System.in);
        System.out.println("Your calculator is now on.");
        double currentResult =0.0;
        System.out.println("The result is currently "+currentResult);
        do {
            menu();
            char[] chars=null;
            boolean success = false;
            expression = input.nextLine();
            chars = expression.toCharArray();
            while (!success) {

                try {
                    if (chars[0] != '+' && chars[0] != '-' && chars[0] != '/' && chars[0] != '*' && chars[0] != 'p' && chars[0] != 'P' && chars[0] != 'R' && chars[0] != 'r') {
                        throw new UnknownOperatorException("Wrong operator ....");
                    }
                    else
                    {
                        success = true;
                    }
                } catch (UnknownOperatorException u) {
                    System.out.println(chars[0]+ " is not a valid character. Result is still "+currentResult);
                    success= false;
                    expression = input.nextLine();
                    chars = expression.toCharArray();
                }
            }


            String[] tokens = expression.split(" ");


            switch (chars[0])
            {
                case '+':
                    try {
                        System.out.print("The result of " + currentResult + " + " + Double.parseDouble(tokens[1]) + " is ");
                        currentResult += Double.parseDouble(tokens[1]);
                        System.out.println(currentResult);
                    }
                    catch (NumberFormatException e)
                    {
                        System.err.println("Not Valid number...");
                        System.out.println(tokens[1] +" is not a valid number. The result is still "+currentResult);
                    }
                    break;
                case '-':
                    try {
                        System.out.print("The result of " + currentResult + " - " + Double.parseDouble(tokens[1]) + " is ");
                        currentResult -= Double.parseDouble(tokens[1]);
                        System.out.println(currentResult);
                    }
                    catch (NumberFormatException e)
                    {
                        System.err.println("Not Valid number...");
                        System.out.println(tokens[1] +" is not a valid number. The result is still "+currentResult);
                    }
                    break;
                case '*':
                    try {
                        System.out.print("The result of " + currentResult + " * " + Double.parseDouble(tokens[1]) + " is ");
                        currentResult *= Double.parseDouble(tokens[1]);
                        System.out.println(currentResult);
                    }
                    catch (NumberFormatException e)
                    {
                        System.err.println("Not Valid number...");
                        System.out.println(tokens[1] +" is not a valid number. The result is still "+currentResult);
                    }

                    break;
                case '/':
                    try {
                        System.out.print("The result of " + currentResult + " / " + Double.parseDouble(tokens[1]) + " is ");

                            double num = Double.parseDouble(tokens[1]);
                            if(num==0)
                                throw new DivideByZeroException();
                            currentResult /= num;
                            System.out.println(currentResult);
                        }
                         catch (DivideByZeroException e)
                         {
                             System.err.println("\nCan't divide by zero...");
                         }
                    catch (NumberFormatException e)
                    {
                        System.err.println("Not Valid number...");
                        System.out.println(tokens[1] +" is not a valid number. The result is still "+currentResult);
                    }
                    break;
                case 'R':
                case 'r':
                    currentResult =0;
                    System.out.println("The calculator has been reset to 0.");
                    break;
                case 'P':
                case 'p':
                    System.out.println("Good Bye...");
                    break;
                    default:
                        System.err.println("ERROR!!! invalid input... try again!");
                        break;
            }
            if(chars[0]=='p'|| chars[0]=='P')
                break;
        }while (true);
    }
    private static void menu()
    {
        System.out.println("Enter an operator (+, -, *, or /) and a number,\n" +
                "     \"R\" to reset, or \"P\" to turn off power  ");
    }
}

//Output

//If you need any help regarding this solution ........... please leave a comment ........ thanks