error Exception in thread "main"

Question

The following code causes an exception and I'm not entirely sure why, any ideas?

Exception

Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 0
at Circle.CircleApp.main

Code

class CircleApp {

    public static void main(String[] args) {
        double rd = Double.parseDouble(args[0]);
        System.out.println("Circle radius = " + rd);

        Circle circle1 = new Circle(rd);

        double cir = circle1.calCircumference();
        double area = circle1.calArea();

        System.out.println("Circumference = " + cir);
        System.out.println("Area = " + area);
    }
}

class Circle {

    private double r;

    Circle(double rd) {
        throw new UnsupportedOperationException("Not supported yet.");
    }

    public void Circle(double r) {

    }

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

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

Error exists in Double.parseDouble(args[0]);, because you didn't specify arguments — Fady Saad, Apr 06 '17 at 03:56
Are you running this from the command line, or through an IDE? If it's an IDE, then do you know how to supply command line arguments in your IDE? If not, then tell us which IDE it is, and someone might give you some instructions. — Dawood ibn Kareem, Apr 06 '17 at 04:07

score 0 · Accepted Answer · edited May 23 '17 at 12:25

It seems that you are lacking really super basic understanding of Java. The real answer here is: step back, and do more studying.

But lets give some details:

You receive that exception, because you are not passing the expected double number to your program when running it. See here for what that means.
In your specific case, you are using NetBeans - see here how to pass arguments in that case.

The point is: your code expects to find a double number, so you can simply pass any kind of number to see what will happend.

What will happen is: another exception, because of

throw new UnsupportedOperationException("Not supported yet.");

But your code is calling exactly that method. So, instead, you need:

public class Circle {
  private double r;
  public Circle(double r) {
    this.r = r;
  }

Then: this here:

public void Circle(double r) {
}

is absolute nonsense. This doesn't even compile.

score 0 · Answer 2 · answered Apr 06 '17 at 04:50

If you run your program from command line, use something like that:

java CircleApp <double number>

For example:

java CircleApp 123.456

If you use an ide, you should configure your run settings. There has to be a field named program arguments or something similar.

score 0 · Answer 3 · answered Apr 06 '17 at 04:59

0

Use this to compile your code:

javac CircleApp.java

java CircleApp 10.0

10.0 can be replaced with any double number of your own

answered Apr 06 '17 at 04:59

mbhargav294

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error Exception in thread "main"

Exception

Code

3 Answers3