Java console calculator

Question

package calc;

import com.sun.tools.corba.se.idl.constExpr.Equal;    //imports .equals(variable)
import java.util.Scanner;    //imports scanners

public class Calc {

    public static void main(String[] args) {
        boolean go = true;    //sets up loop

        while(go)    //creates loop to top
        {
            System.out.println("Hello this is my calculator!");
            System.out.println("To add, type a, to subtract, type s.");
            System.out.println("To multiply, type m, to divide, type d.");

            Scanner scan = new Scanner(System.in);    //sets up scanners
            Scanner scan1 = new Scanner(System.in);


            String action = scan.nextLine();    //tells comp. to take user input

            if("a".equals(action))    //addition
            {
                System.out.println("Now type in the first number you would like to add.");
                int add1 = scan.nextInt();
                System.out.println("Now type the second number.");
                int add2 = scan.nextInt();
                int add3 = add1 + add2;
                System.out.println(add1 + " added to " + add2 + " equals " + add3 + "!");          
            }
            if("s".equals(action))    //subtraction
            {
                System.out.println("Now type in the first number you would like to subtract.");
                int sub1 = scan.nextInt();
                System.out.println("Now type the second number.");
                int sub2 = scan.nextInt();
                int sub3 = sub1 - sub2;
                System.out.println(sub1 + " subtracted bye " + sub2 + " equals " + sub3 + "!"); 
            }
            if("m".equals(action))    //multiplacation
            {
                System.out.println("Now type in the first number you would like to multiply.");
                int mul1 = scan.nextInt();
                System.out.println("Now type the second number.");
                int mul2 = scan.nextInt();
                int mul3 = mul1 * mul2;
                System.out.println(mul1 + " multiplied bye " + mul2 + " equals " + mul3 + "!"); 
            }
            if("d".equals(action))    //division
            {
                System.out.println("Now type in the first number you would like to divide.");
                int div1 = scan.nextInt();
                System.out.println("Now type the second number.");
                int div2 = scan.nextInt();
                int div3 = div1 / div2;
                System.out.println(div1 + " divided bye " + div2 + " equals " + div3 + "!"); 
            }


            System.out.println("Would you like to start over? (yes,no)");           
            String startOver = scan1.nextLine();

            if("no".equals(startOver))
            {
                go = false;
                System.out.println("Bye");
            }
        }
    }                                  
}

• Would it be possible to make this more compact?
• Does this code contain dead code?

Answer 1

You do "the same" for all four choices - time to abstract!

import java.util.Scanner;    //imports scanners

public class Calc {

    enum Op {

        ADD("a", "add", "added to"),
        SUB("s", "subtract", "subtracted by"),
        MUL("m", "multiply", "multiplied by"),
        DIV("d", "divide", "divided by");
        public String key;
        public String command;
        public String result;

        Op(String key, String command, String result) {
            this.key = key;
            this.command = command;
            this.result = result;
        }

        public int eval(int x, int y) {
            switch (this) {
                case ADD:
                    return x + y;
                case SUB:
                    return x - y;
                case MUL:
                    return x * y;
                case DIV:
                    return x / y;
                default:
                    throw new AssertionError();
            }
        }
    }

    public static void main(String[] args) {
        while (true) //creates loop to top
        {
            System.out.println("Hello this is my calculator!");
            System.out.println("To add, type a, to subtract, type s.");
            System.out.println("To multiply, type m, to divide, type d.");

            Scanner scan = new Scanner(System.in);    //sets up scanners
            Scanner scan1 = new Scanner(System.in);


            String action = scan.nextLine();    //tells comp. to take user input

            Op op = null;
            for (Op operation : Op.values()) {
                if (operation.key.equals(action)) {
                    op = operation;
                    break;
                }
            }

            if (op != null) {
                System.out.println("Now type in the first number you would like to " + op.command + ".");
                int x = scan.nextInt();
                System.out.println("Now type the second number.");
                int y = scan.nextInt();
                int z = op.eval(x, y);
                System.out.println(x + " " + op.result + " " + x + " equals " + z + "!");
            }

            System.out.println("Would you like to start over? (yes,no)");
            String startOver = scan1.nextLine();

            if ("no".equals(startOver)) {
                System.out.println("Bye");
                return;
            }
        }
    }
}

So all operation specific information is captured in the Op enums. If you want to add other operations like min, max, and, or, xor or mod, you don't have to introduce new if-blocks, just new enums.

Answer 2

Little things.

You don't need the, go, variable.

while(true) {
  if("no".equals(startOver))
    {
        System.out.println("Bye");
        break;
    }
}

Also, you could use System.out.printf, to make you code a little easier to read.

System.out.printf("%d divided by %d equals %d!\n", div1, div2, div1 / div2);

The newline char is necessary or all your output will appear on one line. Doing the division, addition or multiplication in the output statement will save you the third variable.

I'm not familiar with the, Scanner, class, I don't think you need two of them.

Important note, you code has no error handling, if a user put text were you were expecting a number, the program will exit with an error. You'll want to catch the error on the nextInt calls, tell the user to only input numbers and read from input again.

Answer 3

This line:

import com.sun.tools.corba.se.idl.constExpr.Equal;    //imports .equals(variable)

Is actually not needed/used, and probably not doing what you think it's doing. CORBA is not what one would ordinarily use in a calculator...

The comparison here:

 if("no".equals(startOver))
        {
            go = false;
            System.out.println("Bye");
        }

Actually uses the equals method of the String class. By the way, Kaizen is correct and you don't need two Scanner objects.