Java 'do while' loop not working

Question

I have this code:

import java.util.*; 

public class Vormpjes {

    public static void main(String[] args){
        String vorm;
        String nogmaals;
        double diameter;
        double basis;
        double hoogte;

        Scanner keyboard = new Scanner(System.in);

        do {
            System.out.println("Kies uit de 'cirkel', 'driehoek' of 'vierhoek':");
            vorm = keyboard.nextLine();

            if (vorm.equals("cirkel")){
                System.out.println("Geef een diameter op (in cm)");
                diameter = keyboard.nextDouble();

                cirkel C1 = new cirkel();
                C1.setDiam(diameter);
                System.out.println("De diameter = " + C1.getDiam() + " cm");
                System.out.println("De straal = " + C1.getRadius() + " cm");
                System.out.println("De oppervlakte van de cirkel = " + C1.berekenOpp() + " cm2");
                System.out.println("");
            }

            if (vorm.equals("driehoek")){
                System.out.println("Geef de basis van de driehoek (in cm)");
                basis = keyboard.nextDouble();

                driehoek D1 = new driehoek();
                D1.setBasis(basis);
                System.out.println("Geef de hoogte van de driehoek (in cm)");
                hoogte = keyboard.nextDouble();
                D1.setHoogte(hoogte);
                System.out.println("De oppervlakte = " + D1.berekenOppDriehoek() + " cm2");
                System.out.println("");
            }

            System.out.println("Typ 'J' in als u het programma nogmaals wilt uitvoeren, druk anders op een andere wilekeurige toets.");
            nogmaals = keyboard.nextLine();
        }
        while (nogmaals.equalsIgnoreCase("J"));
    }
}

And the class 'cirkel' (that's how you spell circle in Dutch haha)

public class cirkel extends Vormpjes{

    public double diam;
    public double r;

    //constructor
    public cirkel(){

    }

    public double getDiam(){
        return this.diam;
    }

    public void setDiam(double diam){
        this.diam = diam;
    }

    public double getRadius(){
        r = 0.5 * getDiam();
        return this.r;
    }

    public double berekenOpp(){
        return Math.PI * r * r; 
    }

    public double berekenOmtrek(){
        return 2 * Math.PI * r;
    }

}

When the program asks the user if he wants to run the program again or not, I'm unable to type anything after while condition.

Why is it not working? I don't get errors or anything...

What do you mean "unable to type"? Did the program terminate? — Aify
– Aify, Commented Jun 4, 2015 at 19:37
It's really unclear what's not working here. If you answer J or j the loop will continue. If you answer something else the program terminates, as expected, right? — aioobe
– aioobe, Commented Jun 4, 2015 at 19:38
@WhyCry Google translate :"Type 'Y' if you want to run the program again, otherwise press another key wilekeurige.". And yes in dutch is "Ja". — J Atkin
– J Atkin, Commented Jun 4, 2015 at 19:42
@user3024879, this is because when you've entered 5<enter> and read a double, you still have <enter> in the to-read buffer. Last in your loop, you read a line (to get J or something else), and at this point you'll get the trailing part of the previous input that has not yet been read. The solution is to add a nextLine() after each time you've read a double. — aioobe
– aioobe, Commented Jun 4, 2015 at 19:45

aioobe · Accepted Answer · 2015-06-04 19:50:27Z

2

Each time you call nextDouble() the user will enter a double and press enter. This will put a double and a newline in the buffer. The double is consumed by nextDouble(), but the newline character lingers around until you call nextLine().

In your case this becomes a problem, because when you ask the user for a J (or something else) the "old" newline character is consumed before the user manages to enter anything.

In other words, simply change

diameter = keyboard.nextDouble();

to

diameter = keyboard.nextDouble();
keyboard.nextLine();

to consume the newline character that was entered after the double.

answered Jun 4, 2015 at 19:50

aioobe

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1 Comment

user3024879 Over a year ago

thank you very much, I'm new to Java so I get stuck very easily haha

Verhagen · Accepted Answer · 2015-06-04 19:59:21Z

1

Use the following code, for reading the J/N value, to continue or stop the program.

nogmaals = keyboard.next();

answered Jun 4, 2015 at 19:59

Verhagen

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