Error messages! area(double, double) cannot be applied to ( )

Question

I keep getting these error messages:
area(double,double) in Rectangle cannot be applied to ()
          return "Area: " + Rectangle.area() + "\tCircumference: " + Rectangle.perimeter(); ^
perimeter(double,double) in Rectangle cannot be applied to ()
          return "Area: " + Rectangle.area() + "\tCircumference: " + Rectangle.perimeter();
^
setSides(double,double) in Rectangle cannot be applied to (double)
          R.setSides(input.nextDouble());
^
3 errors
Tool completed with exit code 1
Can anybody tell me why it is doing this? Thanks in advance!
import java.util.Scanner;
public class Rectangle
     public double length;
     public double width;
     public Rectangle()
          length = 0;
          width = 0;
     public double getSides()
          return length;
          return width;
     public void setSides(double length, double width)
          this.length = length;
          this.width = width;
     public double area(double length, double width)
          double area = length * width;
          return area;
     public double perimeter(double length, double width)
          double perimeter = (length * 2) + (width * 2);
          return perimeter;
     public String toString()
          return "Area: " + Rectangle.area() + "\tCircumference: " + Rectangle.perimeter();
     public static void main(String [] args)
          Rectangle R = new Rectangle();
          Scanner input = new Scanner(System.in);
          System.out.println("Enter radius: ");
          R.setSides(input.nextDouble());
          System.out.println(R.toString());
}

Answer 1

Looking at your code more, it looks like what you want to do when you call area is get the area of the Rectangle based on the length and width it already has stored, not what you pass it. So if you take out the parameters like this:
public double area() {
     double area = length * width;
     return area;
}It will use the member variables length and width to calculate area.