how to call an instance method in another class - methods

Question

public class circle
{
double circle1;
double Xvalue;
double Yvalue;
double radius;
public double area = (3.14*(this.radius * this.radius));
public double getArea ()
{
return area;
}
}
//this is my second class that will create the objects
public class tester
{
public static void main(String args [])
{
circle circle1 = new circle();
circle1.Xvalue = 1;
circle1.Yvalue = 2;
circle1.radius = 4;
System.out.println(getArea());
//im not too sure why the print statement won't print the method getArea.
}
}

Answer 1

You need System.out.println(circle1.getArea());, otherwise it's trying to find a method called getArea() in your Tester class which has no such method.
Also, your code will always return an area of 0. This is because of how you initialize your data:
When you create your new circle object it creates xValue and because it is a primitive type (double instead of Double) it defaults to giving it a value of 0 (because it must have some value).
So when it gets down to where you define the area variable at that moment (since it is still creating your object, it does (area = 3.14*(0.0 * 0.0)) which is going to be 0.
What you really want is something more like this:
public class Circle {
double Xvalue;
double Yvalue;
double radius;
public Circle(double xValue, double yValue, double radius) {
this.xValue = xValue;
this.yValue = yValue;
this.radius = radius;
}
public double getArea ()
{
return 3.1415926*(this.radius * this.radius);
}
}
public class Tester
{
public static void main(String[] args)
{
Circle circle1 = new Circle(1, 2, 4);
System.out.println(circle1.getArea());
//im not too sure why the print statement won't print the method getArea.
}
}