Need turning user input into an object

[CodyJava]

I need to ask a user for the radius of a circle. Which will then be turned into an object that i can use in a different class to find different measurements. My question is how do i set the user input to an object. Also how do I refernce back to the class to print out those values. Thanks.

public class Circle {
    double radius;
    final double PI = 3.14159;
    
    Circle(double newradius){
        newradius = radius;
    }
    Circle(){
        radius = 0.0;
    }
    void setRadius(double inputradius){
        radius = inputradius;
    }
    double getRadius(){
        return radius;
    }
    
    double getArea(){
       return PI * radius * radius;
    }
    
   double getDiameter(){
       return radius * 2;
    }
   double getCircumference(){
       return 2 * PI * radius;
   }
}

import java.util.Scanner;
public class CircleTester {
    public static void main(String [] args){
       
        Scanner scan = new Scanner(System.in);
        
        System.out.println("What is the radius of the circle");
        
        
        System.out.println("The circle's area is ");
        
        System.out.println("The circle's diameter is ");
        
        System.out.println("The circumference is ");
    }
}

Thanks again.

[Fou-Lu]

You don't. You create an instance and populate it with primitive data provided by the user (and I doubt you'd ask the user to manually enter serialized data like you can from a file).
So simply ask for the nextDouble off of the scanner, and instantiate the Circle with that provided double: Circle c = new Circle(scan.nextDouble());. That will give you your circle so you can operate on the instance in the following output statements. It doesn't have any error handling in it, but I assume this is for an assignment (in which case error handling has not likely been covered)?

[CodyJava]

Yeah we haven't covered that, but thanks that worked. Sorry I'm kinda confused on this one but is that taking the user input and setting it equal to c? I was hopping to set it equal to radius from the other class. Any idea how I do that. Thanks.

[Fou-Lu]

Nope, what that does is accepts a double from the input, and creates a new instance of Circle providing it with that double.
The only way to modify it (such as taking the radius from another class), is to construct a new instance of circle since there is currently no way to mutate the value of the radius. So if you wanted to create a new circle twice the size of an existing circle, you can use the get method on it: Circle doubleSizeCircle = new Circle(smallerCircleInstance.getRadius());. Now, the current class definition you have for Circle has a package level access to the variables, but I always assume that the variables will be private unless its final.

Edit:
To expand a bit, since the scope of your current circle's radius property is package accessible, you can actually modify it directly:

PHP Code:

Circle c = new Circle();
c.radius = 4.2; 


However, this is not the most ideal since it would also allow me to do:

PHP Code:

c.radius = -4.2; 


which is not a valid raidus.

[CodyJava]

Okay than you for your help so far. I'm not sure if I understand are you saying I can't change the value of radius in the other class?

Here's the constructors I'm trying to call

public class Circle {
    double radius;
    final double PI = 3.14159;
    
    Circle(double newradius){
        newradius = radius;
    }
    Circle(){
        radius = 0.0;
    }
    void setRadius(double inputradius){
        radius = inputradius;
    }
    double getRadius(){
        return radius;
    }
    
    double getArea(){
       return PI * radius * radius;
    }
    
   double getDiameter(){
       return radius * 2;
    }
   double getCircumference(){
       return 2 * PI * radius;
   }
}

Here I'm trying to take the user input and send if back to the Circle class.

import java.util.Scanner;
public class CircleTester {
    public static void main(String [] args){
       
        Scanner scan = new Scanner(System.in);
        Circle c = new Circle();
        System.out.println("What is the radius of the circle");
        
        c.radius = scan.nextDouble(); //can you do it this way 
                
           //Below I'm trying to call the values from the other class not sure if their right

        System.out.println("The circle's area is "+c.getArea());
        
        System.out.println("The circle's diameter is "+c.getDiameter());
        
        System.out.println("The circumference is "+c.getCircumference());
    
    }
}