BAEL-5709 code for the Finding the roots of a quadratic equation article

core-java-modules/core-java-lang-math-3/src/main/java/com/baeldung/math/quadraticequationroot/Complex.java

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+package com.baeldung.math.quadraticequationroot;
+
+public class Complex {
+
+    private double realPart;
+    private double imaginaryPart;
+
+    public Complex(double realPart, double imaginaryPart) {
+        this.realPart = realPart;
+        this.imaginaryPart = imaginaryPart;
+    }
+
+    public static Complex ofReal(double realPart) {
+        return new Complex(realPart, 0);
+    }
+
+    public double getRealPart() {
+        return realPart;
+    }
+
+    public double getImaginaryPart() {
+        return imaginaryPart;
+    }
+
+}

core-java-modules/core-java-lang-math-3/src/main/java/com/baeldung/math/quadraticequationroot/ComplexRootsCalculator.java

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+package com.baeldung.math.quadraticequationroot;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class ComplexRootsCalculator {
+
+    public static List<Complex> getPolynomRoots(Polynom polynom) {
+        List<Complex> roots = new ArrayList<>();
+        double discriminant = polynom.getDiscriminant();
+        if (discriminant > 0) {
+            roots.add(Complex.ofReal((-polynom.getB() - Math.sqrt(discriminant)) / (2 * polynom.getA())));
+            roots.add(Complex.ofReal((-polynom.getB() + Math.sqrt(discriminant)) / (2 * polynom.getA())));
+        } else if (discriminant == 0) {
+            roots.add(Complex.ofReal(-polynom.getB() / (2 * polynom.getA())));
+        } else {
+            roots.add(new Complex(-polynom.getB() / (2* polynom.getA()), -Math.sqrt(-discriminant) / 2* polynom.getA()));
+            roots.add(new Complex(-polynom.getB() / (2* polynom.getA()), Math.sqrt(-discriminant) / 2* polynom.getA()));
+        }
+        return roots;
+    }
+
+}

core-java-modules/core-java-lang-math-3/src/main/java/com/baeldung/math/quadraticequationroot/Polynom.java

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+package com.baeldung.math.quadraticequationroot;
+
+public class Polynom {
+
+    private double a;
+    private double b;
+    private double c;
+
+    public Polynom(double a, double b, double c) {
+        if (a == 0) {
+            throw new IllegalArgumentException("a can not be equal to 0");
+        }
+        this.a = a;
+        this.b = b;
+        this.c = c;
+    }
+
+    public double getA() {
+        return a;
+    }
+
+    public double getB() {
+        return b;
+    }
+
+    public double getC() {
+        return c;
+    }
+
+    public double getDiscriminant() {
+        return b * b - 4 * a * c;
+    }
+
+}

core-java-modules/core-java-lang-math-3/src/main/java/com/baeldung/math/quadraticequationroot/RealRootsCalculator.java

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+package com.baeldung.math.quadraticequationroot;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class RealRootsCalculator {
+
+    public static List<Double> getPolynomRoots(Polynom polynom) {
+        List<Double> roots = new ArrayList<>();
+        double discriminant = polynom.getDiscriminant();
+        if (discriminant > 0) {
+            roots.add((-polynom.getB() - Math.sqrt(discriminant)) / (2 * polynom.getA()));
+            roots.add((-polynom.getB() + Math.sqrt(discriminant)) / (2 * polynom.getA()));
+        } else if (discriminant == 0) {
+            roots.add(-polynom.getB() / (2 * polynom.getA()));
+        }
+        return roots;
+    }
+
+}

core-java-modules/core-java-lang-math-3/src/test/java/com/baeldung/math/quadraticequationroot/ComplexRootsCalculatorUnitTest.java

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+package com.baeldung.math.quadraticequationroot;
+
+import org.junit.jupiter.api.Test;
+
+import java.util.List;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+public class ComplexRootsCalculatorUnitTest {
+
+    @Test
+    void givenPolynomWithStrictlyPositiveDiscriminant_whenGetPolynomRoots_ThenReturnBothRealRoots() {
+        Polynom polynom = new Polynom(1d, 1d, -6d);
+        List<Complex> roots = ComplexRootsCalculator.getPolynomRoots(polynom);
+        assertEquals(2, roots.size());
+        assertTrue(roots.stream().anyMatch(c -> c.getRealPart() == 2d && c.getImaginaryPart() == 0));
+        assertTrue(roots.stream().anyMatch(c -> c.getRealPart() == -3d && c.getImaginaryPart() == 0));
+    }
+
+    @Test
+    void givenPolynomWithDiscriminantEqualsZero_whenGetPolynomRoots_ThenReturnRoot() {
+        Polynom polynom = new Polynom(1d, 4d, 4d);
+        List<Complex> roots = ComplexRootsCalculator.getPolynomRoots(polynom);
+        assertEquals(1, roots.size());
+        assertTrue(roots.get(0).getRealPart() == -2d && roots.get(0).getImaginaryPart() == 0d);
+    }
+
+    @Test
+    void givenPolynomWithStrictlyNegativeDiscriminant_whenGetPolynomRoots_ThenReturnBothComplexRoot() {
+        Polynom polynom = new Polynom(1d, -4d, 8d);
+        List<Complex> roots = ComplexRootsCalculator.getPolynomRoots(polynom);
+        assertEquals(2, roots.size());
+        assertTrue(roots.stream().anyMatch(c -> c.getRealPart() == 2d && c.getImaginaryPart() == 2d));
+        assertTrue(roots.stream().anyMatch(c -> c.getRealPart() == 2d && c.getImaginaryPart() == -2d));
+    }
+
+}

core-java-modules/core-java-lang-math-3/src/test/java/com/baeldung/math/quadraticequationroot/PolynomUnitTest.java

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+package com.baeldung.math.quadraticequationroot;
+
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+public class PolynomUnitTest {
+
+    @Test
+    void givenaEqualTo0_WhenNewPolynom_ThenThrows() {
+        assertThrows(IllegalArgumentException.class, () -> new Polynom(0, 1, 1));
+    }
+
+}

core-java-modules/core-java-lang-math-3/src/test/java/com/baeldung/math/quadraticequationroot/RealRootsCalculatorUnitTest.java

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+package com.baeldung.math.quadraticequationroot;
+
+import org.junit.jupiter.api.Test;
+
+import java.util.Arrays;
+import java.util.List;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+class RealRootsCalculatorUnitTest {
+
+    @Test
+    void givenPolynomWithStrictlyPositiveDiscriminant_whenGetPolynomRoots_ThenReturnBothRoots() {
+        Polynom polynom = new Polynom(1d, 1d, -6d);
+        List<Double> roots = RealRootsCalculator.getPolynomRoots(polynom);
+        assertEquals(2, roots.size());
+        assertTrue(roots.containsAll(Arrays.asList(2d, -3d)));
+    }
+
+    @Test
+    void givenPolynomWithDiscriminantEqualsZero_whenGetPolynomRoots_ThenReturnRoot() {
+        Polynom polynom = new Polynom(1d, 4d, 4d);
+        List<Double> roots = RealRootsCalculator.getPolynomRoots(polynom);
+        assertEquals(1, roots.size());
+        assertTrue(roots.get(0).equals(-2d));
+    }
+
+    @Test
+    void givenPolynomWithStrictlyNegativeDiscriminant_whenGetPolynomRoots_ThenReturnNoRoot() {
+        Polynom polynom = new Polynom(3d, 2d, 5d);
+        List<Double> roots = RealRootsCalculator.getPolynomRoots(polynom);
+        assertEquals(0, roots.size());
+    }
+
+}