[编程入门]自定义函数求一元二次方程 （Java代码）

import java.util.*;
import java.text.DecimalFormat;
public class Main
{
    public static void main(String[] args)
    {
        Scanner in = new Scanner(System.in);
        double a = in.nextDouble();
        double b = in.nextDouble();
        double c = in.nextDouble();
        double sum = b*b - 4*a*c;
        double x1;
        double x2;
        double x11;
        DecimalFormat x = new DecimalFormat("0.000");
        if(sum >= 0)
        {
            b = -b;
            x1 = (b+Math.sqrt(sum))/(2*a);
            x2 = (b-Math.sqrt(sum))/(2*a);
            System.out.print("x1="+x.format(x1)+" x2="+ x.format(x2));
        } 
        else
        {
            x11 = -b/(2*a);
            x1 = (Math.sqrt(-sum))/(2*a);
            x2 = (-Math.sqrt(-sum))/(2*a);
            System.out.print("x1="+x.format(x11)+"+"+x.format(x1)+"i"+" x2="+x.format(x11)+x.format(x2)+"i");
        }
    }
}