Having trouble with primitive type 'long'

[Sizzlewump]

Please help with my coding chaos! I'm getting some errors in my code like:

Spiral.java:25: possible loss of precision
found : long
required: int
int yNeg = hCen - 20 - (20 * fib(j));

I understand that I gave it the wrong data type but I'm not sure how to cast (is that the right term?) an int to a long. What are your recommendations? Here is my code:

/* Created by John Thrush and user3266259 (of stackOverflow)
4/06/2016
Spiral is an app that displays a rectangular spiral
and should incorporate growth in the fibonacci series
based on the hardcoded value of "N" so as not to draw 
through infinity. */
import java.awt.*; 
import javax.swing.JPanel;
import javax.swing.JFrame;

public class Spiral extends JPanel
{
   public void paintComponent(Graphics g)
   {
      long w = getSize().width;
      long h = getSize().height;
      long wCen = w / 2;
      long hCen = h / 2;
         int N = 13;
         for (int j = 1; j <= N; j++)
		   {
			   int xPos = wCen + (20 * fib(j));
		      int xNeg = wCen - 20 - (20 * fib(j));
		      int yPos = hCen + 20 + (20 * fib(j));
		      int yNeg = hCen - 20 - (20 * fib(j));
				
            System.out.println(j + ": " + fib(j));
            g.drawLine(xPos, yNeg, xPos, yPos);
		      g.setColor(Color.blue);
            g.drawLine(xPos, yPos, xNeg, yPos);
			   g.setColor(Color.red);
            g.drawLine(xNeg, yPos, xNeg, yNeg);
			   g.setColor(Color.green);
            g.drawLine(xNeg, yNeg, xPos, yNeg);
		      g.setColor(Color.cyan);
			}	
   }
	
   public static long fib(int n) 
	{
      if (n <= 1) return n;
      else return fib(n-1) + fib(n-2);
   }
	
   public static void main(String[] args)
   {
      Spiral panel = new Spiral();
      JFrame frame = new JFrame();
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      frame.add(panel);      
      frame.setSize(1000, 1000); 
      frame.setVisible(true);     
   }
}

Thanks!

[jim829]

Yes you cast it like this.

long a = 20;
int b = (int)a;

In your case the entire right side is converted to a long so you should put it in () and cast the entire expression.

Regards,
Jim

[Sizzlewump]

Thanks Jim! But when I do:

int xPos = int(wCen + (20 * fib(j)));

for each of of my variables, I get errors like:

Spiral.java:22: '.class' expected
int xPos = int(wCen + (20 * fib(j)));

Have I done something wrong?

[Sizzlewump]

Oops, I misinterpreted your advice, Jim. This seems to work now, thanks again:

/* Created by John Thrush and user3266259 (of stackOverflow)
4/06/2016
Spiral is an app that displays a rectangular spiral
and should incorporate growth in the fibonacci series
based on the hardcoded value of "N" so as not to draw 
through infinity. */
import java.awt.*; 
import javax.swing.JPanel;
import javax.swing.JFrame;

public class Spiral extends JPanel
{
   public void paintComponent(Graphics g)
   {
      int w = getSize().width;
      int h = getSize().height;
      int wCen = w / 2;
      int hCen = h / 2;
      int N = 13;
         for (int j = 1; j <= N; j++)
		   {
			   int xPos = (int)(wCen + (20 * fib(j)));
		      int xNeg = (int)(wCen - 20 - (20 * fib(j)));
		      int yPos = (int)(hCen + 20 + (20 * fib(j)));
		      int yNeg = (int)(hCen - 20 - (20 * fib(j)));
				
            System.out.println(j + ": " + fib(j));
            g.drawLine(xPos, yNeg, xPos, yPos);
		      g.setColor(Color.blue);
            g.drawLine(xPos, yPos, xNeg, yPos);
			   g.setColor(Color.red);
            g.drawLine(xNeg, yPos, xNeg, yNeg);
			   g.setColor(Color.green);
            g.drawLine(xNeg, yNeg, xPos, yNeg);
		      g.setColor(Color.cyan);
			}	
   }
	
   public static long fib(int n) 
	{
      if (n <= 1) return n;
      else return fib(n-1) + fib(n-2);
   }
	
   public static void main(String[] args)
   {
      Spiral panel = new Spiral();
      JFrame frame = new JFrame();
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      frame.add(panel);      
      frame.setSize(1000, 1000); 
      frame.setVisible(true);     
   }
}

[Tolls]

A simpler solution, since you are not using longs anyway, would be to get fib to return an int, unless it simply has to return a long for some reason?

[Sizzlewump]

A simpler solution, since you are not using longs anyway, would be to get fib to return an int, unless it simply has to return a long for some reason?

Yes, I it's necessary to use long for when I change the value of N to larger values. I was kind of just playing with the upper limits of memory in Java. When N > 42, you can start to notice the time taken for the calculations of fib.

[Pavlo]

Hello

On left side of your equation

int yNeg = hCen - 20 - (20 * fib(j));

you state int type, but on right side the type is long. This means if you cast to int, you can lost your long value! So, I would consider such cast only if this *** hCen - 20 - (20 * fib(j)) *** always smaller than int type limit. Any way I would think about appropriate use of int and long types, instead of cast.

[Tolls]

Yes, I it's necessary to use long for when I change the value of N to larger values. I was kind of just playing with the upper limits of memory in Java. When N > 42, you can start to notice the time taken for the calculations of fib.

But then you have values > an int, so when you cast it'll be wrong anyway.