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Merge pull request #12678 from thibaultfaure/article/BAEL-5709-find-roots-of-a-quadratic-equation

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BAEL-5709 code for the Finding the roots of a quadratic equation article
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davidmartinezbarua 2022-09-05 21:03:35 -03:00 committed by GitHub
commit c1a759900e
7 changed files with 190 additions and 0 deletions
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25
core-java-modules/core-java-lang-math-3/src/main/java/com/baeldung/math/quadraticequationroot/Complex.java Normal file
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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;
}
}

23
core-java-modules/core-java-lang-math-3/src/main/java/com/baeldung/math/quadraticequationroot/ComplexRootsCalculator.java Normal file
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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;
}
}

34
core-java-modules/core-java-lang-math-3/src/main/java/com/baeldung/math/quadraticequationroot/Polynom.java Normal file
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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;
}
}

20
core-java-modules/core-java-lang-math-3/src/main/java/com/baeldung/math/quadraticequationroot/RealRootsCalculator.java Normal file
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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;
}
}

38
core-java-modules/core-java-lang-math-3/src/test/java/com/baeldung/math/quadraticequationroot/ComplexRootsCalculatorUnitTest.java Normal file
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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));
}
}

14
core-java-modules/core-java-lang-math-3/src/test/java/com/baeldung/math/quadraticequationroot/PolynomUnitTest.java Normal file
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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));
}
}

36
core-java-modules/core-java-lang-math-3/src/test/java/com/baeldung/math/quadraticequationroot/RealRootsCalculatorUnitTest.java Normal file
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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());
}
}