Java Swing GUI for equation 5((θ/β) - cos(2πθ/β))

Question

I am trying to create a GUI using Java Swing for the mathematical equation 5((θ/β) - cos(2πθ/β)).

Initially I started using a simple cosine function and created the GUI and it is working correctly. Here is my program for cosine function:

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Graphics;

import javax.swing.JFrame;
import javax.swing.JPanel;

public class SimpleCosWave extends JFrame {
    public SimpleCosWave() {
        setLayout(new BorderLayout());
        add(new CosGraph(), BorderLayout.CENTER);
    }

    public static void main(String[] args) {
        SimpleCosWave frame = new SimpleCosWave();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setSize(600, 600);
        frame.setVisible(true);
        frame.setLocationRelativeTo(null);
        frame.setTitle("SineWave");
    }

    class CosGraph extends JPanel {
        public void paintComponent(Graphics g) {
            int xBase = 100;
            int top = 100; 
            int yScale = 100;
            int xAxis = 360; 

            int yBase = top + yScale;
            int x, y;

            g.drawLine(xBase, top, xBase, top + 2 * yScale);
            g.drawLine(xBase, yBase, xBase + xAxis, yBase);

            g.setColor(Color.red);

            for (int i = 0; i < xAxis; i++) {
                x = xBase + i;
                y =  yBase - (int) Math.cos(Math.toRadians(i)) * yScale;
                g.drawLine(x,y,x,y);
            }
        }
    }
}

This program is working fine and I can get the cos graph on swing GUI.

Now I am trying to extend this program to support the equation - 5((θ/β) - cos(2πθ/β)) where θ ranges from 0 to 360 degrees and value of β is such that it is 0 < β < 360 .

I have changed the above code to calculate the y co-ordinate to support this equation like this:

y =  yBase - getValue(i) * yScale;

here getValue method is:

private int getValue(int theta) {
            int beta = 45;
            double b = (theta/beta);

            double angle = 2*Math.PI*(b);

            double c = Math.cos(angle);

            double result = 5*(b-c);
            return (int)result;
        }

When I do this change then I am not getting any proper graph or wave, instead I am getting a horizontal line.

Can someone please help me where I am doing mistake in this code?

Answer 1

Replace:

double b = (theta/beta);

with

double b = (theta/(double)beta);

and see if this helps.

See How to make the division of 2 ints produce a float instead of another int? for more info.

Answer 2

As Wim Delauwe points out, when dividing an int by an int, you are doing integer division. For example, 45 / 90 results in an int value of zero . However, 45.0 / 90.0 evaluates to the double value of 0.5. If either operand is a double, the other is coerced to a double, so 45 / 90.0 will also yield 0.5.

Similarly, because your values are in a relatively small range, you should not truncate a value to an integer until you have calculated the exact pixel corresponding to the value, to preserve the precision. Thus, getValue should have a return type of double, and it should return result without casting it.

Then, in your drawing code, you would do the cast:

y = yBase - (int) (getValue(i) * yScale);

However, as David Wallace points out, getValue(i) seems to return values between roughly -5 and +43. Multiplying those values by yScale is going to create a very vertically stretched graph.

You could just hard-code normalization:

y = yBase - (int) (getValue(i) / 43.0 * yScale);

I would opt to calculate the largest y value, and normalize them by that:

double maxY = 0;
for (int i = 0; i < xAxis; i++) {
    maxY = Math.max(maxY, Math.abs(getValue(i)));
}

for (int i = 0; i < xAxis; i++) {
    x = xBase + i;
    y = yBase - (int) (getValue(i) / maxY * yScale);
    g.drawLine(x,y,x,y);
}