From 3bf9d581148dd42256c0e78418c9f901bccc63de Mon Sep 17 00:00:00 2001
From: BanulaKumarage <banula.19@cse.mrt.ac.lk>
Date: Sun, 5 Oct 2025 00:12:44 +0530
Subject: [PATCH] Added CoordinateConverter utility class for Cartesian and
 Polar coordinate conversions

---
 .../conversions/CoordinateConverter.java      | 57 +++++++++++++++++++
 .../conversions/CoordinateConverterTest.java  | 34 +++++++++++
 2 files changed, 91 insertions(+)
 create mode 100644 src/main/java/com/thealgorithms/conversions/CoordinateConverter.java
 create mode 100644 src/test/java/com/thealgorithms/conversions/CoordinateConverterTest.java

diff --git a/src/main/java/com/thealgorithms/conversions/CoordinateConverter.java b/src/main/java/com/thealgorithms/conversions/CoordinateConverter.java
new file mode 100644
index 000000000000..2766a3a1cf89
--- /dev/null
+++ b/src/main/java/com/thealgorithms/conversions/CoordinateConverter.java
@@ -0,0 +1,57 @@
+package com.thealgorithms.conversions;
+
+/**
+ * A utility class to convert between Cartesian and Polar coordinate systems.
+ *
+ * <p>This class provides methods to perform the following conversions:
+ * <ul>
+ *   <li>Cartesian to Polar coordinates</li>
+ *   <li>Polar to Cartesian coordinates</li>
+ * </ul>
+ *
+ * <p>The class is final and cannot be instantiated.
+ */
+public final class CoordinateConverter {
+
+    private CoordinateConverter() {
+        // Prevent instantiation
+    }
+
+    /**
+     * Converts Cartesian coordinates to Polar coordinates.
+     *
+     * @param x the x-coordinate in the Cartesian system; must be a finite number
+     * @param y the y-coordinate in the Cartesian system; must be a finite number
+     * @return an array where the first element is the radius (r) and the second element is the angle (theta) in degrees
+     * @throws IllegalArgumentException if x or y is not a finite number
+     */
+    public static double[] cartesianToPolar(double x, double y) {
+        if (!Double.isFinite(x) || !Double.isFinite(y)) {
+            throw new IllegalArgumentException("x and y must be finite numbers.");
+        }
+        double r = Math.sqrt(x * x + y * y);
+        double theta = Math.toDegrees(Math.atan2(y, x));
+        return new double[] {r, theta};
+    }
+
+    /**
+     * Converts Polar coordinates to Cartesian coordinates.
+     *
+     * @param r the radius in the Polar system; must be non-negative
+     * @param thetaDegrees the angle (theta) in degrees in the Polar system; must be a finite number
+     * @return an array where the first element is the x-coordinate and the second element is the y-coordinate in the Cartesian system
+     * @throws IllegalArgumentException if r is negative or thetaDegrees is not a finite number
+     */
+    public static double[] polarToCartesian(double r, double thetaDegrees) {
+        if (r < 0) {
+            throw new IllegalArgumentException("Radius (r) must be non-negative.");
+        }
+        if (!Double.isFinite(thetaDegrees)) {
+            throw new IllegalArgumentException("Theta (angle) must be a finite number.");
+        }
+        double theta = Math.toRadians(thetaDegrees);
+        double x = r * Math.cos(theta);
+        double y = r * Math.sin(theta);
+        return new double[] {x, y};
+    }
+}
diff --git a/src/test/java/com/thealgorithms/conversions/CoordinateConverterTest.java b/src/test/java/com/thealgorithms/conversions/CoordinateConverterTest.java
new file mode 100644
index 000000000000..e41e9160478d
--- /dev/null
+++ b/src/test/java/com/thealgorithms/conversions/CoordinateConverterTest.java
@@ -0,0 +1,34 @@
+package com.thealgorithms.conversions;
+
+import static org.junit.jupiter.api.Assertions.assertArrayEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.CsvSource;
+
+public class CoordinateConverterTest {
+
+    @ParameterizedTest
+    @CsvSource({"0, 0, 0, 0", "1, 0, 1, 0", "0, 1, 1, 90", "-1, 0, 1, 180", "0, -1, 1, -90", "3, 4, 5, 53.13010235415599"})
+    void testCartesianToPolar(double x, double y, double expectedR, double expectedTheta) {
+        assertArrayEquals(new double[] {expectedR, expectedTheta}, CoordinateConverter.cartesianToPolar(x, y), 1e-9);
+    }
+
+    @ParameterizedTest
+    @CsvSource({"1, 0, 1, 0", "1, 90, 0, 1", "1, 180, -1, 0", "1, -90, 0, -1", "5, 53.13010235415599, 3, 4"})
+    void testPolarToCartesian(double r, double theta, double expectedX, double expectedY) {
+        assertArrayEquals(new double[] {expectedX, expectedY}, CoordinateConverter.polarToCartesian(r, theta), 1e-9);
+    }
+
+    @ParameterizedTest
+    @CsvSource({"NaN, 1", "1, NaN", "Infinity, 1", "1, Infinity", "-Infinity, 1", "1, -Infinity"})
+    void testCartesianToPolarInvalidInputs(double x, double y) {
+        assertThrows(IllegalArgumentException.class, () -> CoordinateConverter.cartesianToPolar(x, y));
+    }
+
+    @ParameterizedTest
+    @CsvSource({"-1, 0", "1, NaN", "1, Infinity", "1, -Infinity"})
+    void testPolarToCartesianInvalidInputs(double r, double theta) {
+        assertThrows(IllegalArgumentException.class, () -> CoordinateConverter.polarToCartesian(r, theta));
+    }
+}