Java Kotlin --> Plotting Two Curves on the Same Plot

[jedishrfu]

Here's a Kotlin program that uses Java Swing and Java AWT to plot sine and cosine curves for the interval [0,2π].

The program creates a window with a panel where both curves are drawn:

• Uses JFrame and JPanel for GUI rendering.
• Uses Graphics to draw the sine and cosine curves.
• Automatically scales the graph to fit within the window.

Kotlin Code:​

[CODE lang="java" title="Using Kotlin to plot Sine and Cosine on the same Chart"]
import java.awt.*
import javax.swing.*
import kotlin.math.*

class SineCosinePlot : JPanel() {
private val padding = 50 // Padding around the plot area
private val steps = 100 // Number of points to plot

override fun paintComponent(g: Graphics) {
super.paintComponent(g)
val g2 = g as Graphics2D
g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON)

val width = width - 2 * padding
val height = height - 2 * padding
val centerX = padding
val centerY = height / 2 + padding

// Draw axes
g2.color = Color.BLACK
g2.stroke = BasicStroke(2f)
g2.drawLine(centerX, centerY, centerX + width, centerY) // X-axis
g2.drawLine(centerX, padding, centerX, centerY + height / 2) // Y-axis

// Draw grid
g2.color = Color.LIGHT_GRAY
for (i in 1..4) {
val x = centerX + i * width / 4
val y = centerY - i * height / 4
g2.drawLine(x, padding, x, centerY + height / 2) // Vertical grid
g2.drawLine(centerX, y, centerX + width, y) // Horizontal grid
}

// Draw sine and cosine curves
drawFunction(g2, centerX, centerY, width, height, Color.RED) { x -> sin(x) }
drawFunction(g2, centerX, centerY, width, height, Color.BLUE) { x -> cos(x) }

// Draw labels
g2.color = Color.BLACK
g2.font = Font("Arial", Font.BOLD, 14)
g2.drawString("0", centerX - 10, centerY + 15)
g2.drawString("π", centerX + width / 2 - 5, centerY + 15)
g2.drawString("2π", centerX + width - 10, centerY + 15)
g2.drawString("1", centerX - 20, padding)
g2.drawString("-1", centerX - 25, centerY + height / 2)
}

private fun drawFunction(
g2: Graphics2D, centerX: Int, centerY: Int, width: Int, height: Int, color: Color,
function: (Double) -> Double
) {
g2.color = color
g2.stroke = BasicStroke(2f)

val stepSize = (2 * Math.PI) / steps
val scaleX = width / (2 * Math.PI) // Scale X to fit 0 to 2π
val scaleY = height / 2.0 // Scale Y to fit -1 to 1

var prevX = centerX
var prevY = (centerY - function(0.0) * scaleY).toInt()

for (i in 1..steps) {
val x = i * stepSize
val screenX = (centerX + x * scaleX).toInt()
val screenY = (centerY - function(x) * scaleY).toInt()
g2.drawLine(prevX, prevY, screenX, screenY)
prevX = screenX
prevY = screenY
}
}
}

fun main() {
SwingUtilities.invokeLater {
val frame = JFrame("Sine & Cosine Plot")
frame.defaultCloseOperation = JFrame.EXIT_ON_CLOSE
frame.setSize(800, 600)
frame.add(SineCosinePlot())
frame.isVisible = true
}
}
[/CODE]

Explanation:​

1. paintComponent(Graphics g):
   • This method is overridden when drawing the sine and cosine curves.
2. Axes Drawing:
   • Draws the x-axis and y-axis with labels for 0,𝜋, and 2𝜋.
3. Sine and Cosine Curves:
   • The graph is drawn by iterating over screen pixels and mapping them to the sine/cosine function.
   • x values are scaled using SCALE_X, and
   • y values are scaled using SCALE_Y.
   • drawLine() is used to connect consecutive points smoothly.

Output:​

• A red sine wave and a blue cosine wave are displayed in a window.
• Axes labeled at 0,𝜋, and 2𝜋.
• The graph scales dynamically to fit in the window.

Solution Credits​

Proposed by: @hagopbul
Coded by: @ChatGPT
Reviewed by: @jedishrfu