用java设计并实现一元二次方程类 若不是一元二次方程，抛出异常 测试该类，若有实根求之，若没有，显示“无实根”

好的，以下是用 Java 设计并实现一元二次方程类的代码：

public class QuadraticEquation {
    private double a, b, c;

    public QuadraticEquation(double a, double b, double c) throws Exception {
        if (a == 0) {
            throw new Exception("Not a quadratic equation!");
        }
        this.a = a;
        this.b = b;
        this.c = c;
    }

    public double getDiscriminant() {
        return b * b - 4 * a * c;
    }

    public double getRoot1() {
        return (-b + Math.sqrt(getDiscriminant())) / (2 * a);
    }

    public double getRoot2() {
        return (-b - Math.sqrt(getDiscriminant())) / (2 * a);
    }

    public String solve() {
        double discriminant = getDiscriminant();
        if (discriminant < 0) {
            return "No real roots!";
        } else if (discriminant == 0) {
            return "One real root: " + getRoot1();
        } else {
            return "Two real roots: " + getRoot1() + " and " + getRoot2();
        }
    }
}

你可以使用以下代码来测试该类：

public class TestQuadraticEquation {
    public static void main(String[] args) {
        try {
            QuadraticEquation qe1 = new QuadraticEquation(1, -3, 2);
            System.out.println(qe1.solve()); // Two real roots: 2.0 and 1.0
            QuadraticEquation qe2 = new QuadraticEquation(1, 2, 1);
            System.out.println(qe2.solve()); // One real root: -1.0
            QuadraticEquation qe3 = new QuadraticEquation(1, 1, 1);
            System.out.println(qe3.solve()); // No real roots!
        } catch (Exception e) {
            System.out.println(e.getMessage());
        }
    }
}

如果输入的系数是一元二次方程的系数，那么程序会输出方程的根；如果输入的系数不是一元二次方程的系数，程序会抛出异常并输出错误信息。