用java编程，求axx+bx+c=0的根 考虑d=b*b-4ac，大于0，等于0，小于0三种情况

public class QuadraticEquation {
public static void main(String[] args) {
QuadraticEquation qe = new QuadraticEquation();
double[] d = qe.calculate(1, 3, 10);
if (null == d) {
System.out.println("no real number results");
} else if (d.length == 1) {
System.out.println("x=" + d[0]);
} else {
System.out.println("x1=" + d[0] + ", x2=" + d[1]);
}
}

private double[] calculate(double a, double b, double c) {
double[] d;
double delta = Math.pow(b, 2) - 4 * a * c;

if (delta > 0) {
d = new double[2];
d[0] = (0 - b + Math.sqrt(delta)) / (2 * a);
d[1] = (0 + b + Math.sqrt(delta)) / (2 * a);
} else if (delta == 0) {
d = new double[1];
d[0] = b / (2 * a);
} else {
d = null;
}
return d;
}
}