EquationSolver.java

/**
 * Program for solving quadratic equations of view:
 * a*x^2+b*x+c=0 where a,b,c represent polynomial coefficients
 * Checks correctness of arguments ,then prints out roots or root of equation.
 */
public class EquationSolver {

    public static void main(String[] args) {
        solveEquation(1, 6, 9);
    }

    private static void solveEquation(double a, double b, double c) {
        if (isEquationIncorrect(a)) {
            System.out.println("Equation must be quadratic.\n Please check entered parameters and try again!");
        } else {
            double d = evaluateDiscriminant(a, b, c);
            if (hasRoots(d)) {
                yieldRoots(a, b, c, d);
            } else {
                System.out.println("Particularly this equation has no solution!");
            }
        }
    }

    //roots are defined iff D>=0;
    private static boolean hasRoots(double d) {
        return d >= 0;
    }

    private static void yieldRoots(double a, double b, double c, double d) {
        if (d > 0) {
            double x1 = ((-b) + Math.sqrt(d)) / (2 * a);
            double x2 = ((-b) - Math.sqrt(d)) / (2 * a);
            System.out.println("Roots of equation are \n" + "x1=" + x1 + "\n" + "x2=" + x2);
        } else if (d == 0) {
            double x = -b / (2 * a);
            System.out.println("Equation has single root \n" + "x=" + x);
        }
    }

    private static double evaluateDiscriminant(double a, double b, double c) {
        double d = b * b - 4 * a * c;
        return d;
    }

    private static boolean isEquationIncorrect(double a) {
        return a == 0;
    }

}