how to re-run java program after reading user input [duplicate]

Question

i'm developing a java program that shows area and perimeter of two rectangle with fixed width&length, current date and reads input from user to solve a linear equation. I was able to ask a user if they want to re-run the program or not. the problem is that if they input y or Y, the program runs, but if the user enters anything els the program quits. I'd like to check this input and see if:

1- it's a y or Y, re-run

2- it's n or N, quit

3- neither 1 nor 2, ask the user again if he/she wants to re-run the program of not.

Here's my code:

    public static void main(String[] args) {

    char ch = 'y'; 

    GregorianCalendar calendar = new GregorianCalendar();

    LinearEquation le = new LinearEquation(1.0,1.0,1.0,1.0,1.0,1.0);

    Rectangle rec1 = new Rectangle(4.0,40.0);
    Rectangle rec2 = new Rectangle(3.5,35.9);        

    Scanner input = new Scanner(System.in);

    Double a, b, c, d, e,f;

do{

    System.out.println("First rectangle info is: ");
    System.out.print(" width is: "+ rec1.getWidth() + 
                   "\n height is: " + rec1.getHeight()+ 
                   "\n Area is: "+ rec1.getArea() +
                   "\n Perimeter is: " + rec1.getPerimeter());

    System.out.println();
    System.out.println();

    System.out.println("Second rectangle info is: ");
    System.out.print(" width is: "+ rec2.getWidth() + 
                   "\n height is: " + rec2.getHeight()+ 
                   "\n Area is: "+ rec2.getArea() +
                   "\n Perimeter is: " + rec2.getPerimeter());

    System.out.println();

    System.out.println("Current date is: " + calendar.get(GregorianCalendar.DAY_OF_MONTH) +   
    "-" + (calendar.get(GregorianCalendar.MONTH) + 1)+ 
    "-" + calendar.get(GregorianCalendar.YEAR));

    System.out.println("Date after applying 1234567898765L to setTimeInMillis(long) is: ");

    calendar.setTimeInMillis(1234567898765L);
    System.out.println(calendar.get(GregorianCalendar.DAY_OF_MONTH) +   
    "-" + (calendar.get(GregorianCalendar.MONTH) + 1)+ 
    "-" + calendar.get(GregorianCalendar.YEAR));

    System.out.println();
    System.out.println("Please, enter a, b, c, d, e and f to solve the equation:");

    try{

        System.out.println("a: ");        
        a = input.nextDouble();

        System.out.println("b: ");
        b = input.nextDouble();

        System.out.println("c: ");
        c = input.nextDouble(); 

        System.out.println("d: ");
        d = input.nextDouble();

        System.out.println("e: ");
        e = input.nextDouble();

        System.out.println("f: ");
        f = input.nextDouble();

        le.setA(a);
        le.setB(b);
        le.setC(c);
        le.setD(d);
        le.setE(e);
        le.setF(f);

        if(le.isSolvable()){

            System.out.println("x is: "+ le.getX() + "\ny is: "+ le.getY());

        }else { 

            System.out.println("The equation has no solution.");
        }   

        //System.out.println("Would you like to re-run the program( y or n)");
        //ch = input.next().charAt(0);
}
catch (Exception ee) {

 System.out.println("Invalid input");
 //System.out.println("Would you like to re-run the program( y or n)");
 ch = input.next().charAt(0);     
  }

     System.out.println("Would you like to re-run the program( y or any other       input to quit)");
 ch = input.next().charAt(0);

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

  }

Note that the do-while loop is considered as bad practice because to see the continuation condition, you have to scroll down to the very end of it. Rather use while. — Monkey Supersonic
– Monkey Supersonic, Commented Feb 25, 2017 at 21:24

davidxxx · Accepted Answer · 2017-02-25 21:14:55Z

1

You can add a do while when you asks the user whether if he wants to repeat the program.

Besides, instead of specifying both uppercase and lowercase in statement : while(ch == 'y' || ch == 'Y'); you can use Character.toLowerCase() method to reduce the number of tests to perform.

    do {
        System.out.println("Would you like to re-run the program( y or any other input to quit)");
        ch = input.next().charAt(0);
        ch = Character.toLowerCase(ch);
    } while (ch != 'y' && ch != 'n');

Now your code could look like that :

do {
      ....
        do {
            System.out.println("Would you like to re-run the program( y or any other input to quit)");
            ch = input.next().charAt(0);
            ch = Character.toLowerCase(ch);

           } while (ch != 'y' && ch != 'n');

   } while (ch == 'y');

answered Feb 25, 2017 at 21:14

davidxxx

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2 Comments

user2066392 Over a year ago

that worked!! Thanks

davidxxx Over a year ago

You are kind and are welcome :)

Monkey Supersonic · Accepted Answer · 2017-02-25 21:12:24Z

0

At the end of your loop (but still IN your loop), you could do something like

ch = 'x'; // Just a dummy value

while (ch != 'y' && ch != 'n') {
    System.out.prinln("Enter y or n:");
    ch = input.next().charAt(0);
}

if (ch == 'n') {
    break;
}

answered Feb 25, 2017 at 21:12

Monkey Supersonic

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1 Comment

user2066392 Over a year ago

I didn't try your suggestion but REALLY THANKS FOR YOUR COMMENT!!

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