Added sample code for complex number addition and multiplication

core-java-modules/core-java-numbers-7/src/test/java/com/baeldung/complexnumbers/ComplexNumberAddMultiplyUnitTest.java

@@ -0,0 +1,90 @@
+package com.baeldung.complexnumbers;
+
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.CsvSource;
+
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
+
+class ComplexNumber {
+    public long real;
+    public long imaginary;
+
+    public ComplexNumber(long a, long b) {
+        this.real = a;
+        this.imaginary = b;
+    }
+
+    public ComplexNumber(String complexNumberStr) {
+        Pattern pattern = Pattern.compile("(-?\\d+)\\s*[+]\\s*(-?\\d+)\\s*i|(-?\\d+)\\s*i\\s*[+]\\s*(-?\\d+)");
+        Matcher matcher = pattern.matcher(complexNumberStr);
+        if (matcher.find()) {
+            // Extract real and imaginary parts
+            long realPart;
+            long imaginaryPart;
+            if (matcher.group(1) != null && matcher.group(2) != null) {
+                realPart = Long.parseLong(matcher.group(1)); // Group 1 is the real part
+                imaginaryPart = Long.parseLong(matcher.group(2)); // Group 2 is the imaginary part
+            } else {
+                realPart = Long.parseLong(matcher.group(4)); // Group 4 is the real part
+                imaginaryPart = Long.parseLong(matcher.group(3)); // Group 3 is the imaginary part
+            }
+            this.real = realPart;
+            this.imaginary = imaginaryPart;
+        } else {
+            throw new IllegalArgumentException("String does not match the complex number pattern of `a+bi` or `bi+a`.");
+        }
+    }
+
+    public long getReal() {
+        return real;
+    }
+
+    public long getImaginary() {
+        return imaginary;
+    }
+
+    public String toString() {
+        return real + "+" + imaginary + "i";
+    }
+
+    public ComplexNumber add(ComplexNumber that) {
+        return new ComplexNumber(real + that.getReal(), imaginary + that.getImaginary());
+    }
+
+    public ComplexNumber multiply(ComplexNumber that) {
+        long newReal = this.real * that.real - this.imaginary * that.imaginary;
+        long newImaginary = this.real * that.imaginary + this.imaginary * that.real;
+        return new ComplexNumber(newReal, newImaginary);
+    }
+
+    public boolean isSame(ComplexNumber that) {
+        return this.real == that.real && this.imaginary == that.imaginary;
+    }
+
+}
+
+public class ComplexNumberAddMultiplyUnitTest {
+
+    @ParameterizedTest(name = "Multiplying {0} and {1}")
+    @CsvSource({
+            "3+2i, 1+7i, -11+23i",
+            "1+1i, 1+1i, 0+2i",
+            "2i+3, 1+7i, 23i+-11",
+            "2i  +3, 1 +    7i,   23i+   -11",
+            "0+5i, 3+0i, 0+15i",
+            "0+0i, -2+0i, 0+0i",
+            "-3+2i, 1-7i, -23-23i"
+    })
+    public void sum_two_complex_numbers(String complexStr1, String complexStr2, String expectedStr) {
+        ComplexNumber complex1 = new ComplexNumber(complexStr1);
+        ComplexNumber complex2 = new ComplexNumber(complexStr2);
+        ComplexNumber expected = new ComplexNumber(expectedStr);
+        ComplexNumber multiplied = complex1.multiply(complex2);
+        System.out.println(multiplied.toString());
+        Assertions.assertTrue(multiplied.isSame(expected));
+    }
+
+}