Create SumOfOddNumbers.java

src/main/java/com/thealgorithms/maths/SumOfOddNumbers.java

@@ -0,0 +1,25 @@
+package com.thealgorithms.maths;
+
+/**
+ * This program calculates the sum of the first n odd numbers.
+ *
+ * https://www.cuemath.com/algebra/sum-of-odd-numbers/
+ */
+
+public final class SumOfOddNumbers {
+    private SumOfOddNumbers() {
+    }
+
+    /**
+     * Calculate sum of the first n odd numbers
+     *
+     * @param n the number of odd numbers to sum
+     * @return sum of the first n odd numbers
+     */
+    public static int sumOfFirstNOddNumbers(final int n) {
+        if (n < 0) {
+            throw new IllegalArgumentException("n must be non-negative.");
+        }
+        return n * n;
+    }
+}

src/test/java/com/thealgorithms/maths/SumOfOddNumbersTest.java

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+package com.thealgorithms.maths;
+
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+import java.util.stream.Stream;
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.Arguments;
+import org.junit.jupiter.params.provider.MethodSource;
+
+public class SumOfOddNumbersTest {
+
+    @ParameterizedTest
+    @MethodSource("inputStream")
+    void sumOfFirstNOddNumbersTests(int expected, int input) {
+        Assertions.assertEquals(expected, SumOfOddNumbers.sumOfFirstNOddNumbers(input));
+    }
+
+    private static Stream<Arguments> inputStream() {
+        return Stream.of(Arguments.of(1, 1), Arguments.of(4, 2), Arguments.of(9, 3), Arguments.of(16, 4), Arguments.of(25, 5), Arguments.of(100, 10));
+    }
+
+    @Test
+    public void testSumOfFirstNOddNumbersThrowsExceptionForNegativeInput() {
+        assertThrows(IllegalArgumentException.class, () -> SumOfOddNumbers.sumOfFirstNOddNumbers(-1));
+    }
+}