为什么错误 interface Shape{ void zhouchang(); void mianji(); } class sanjiaoxing implements Shape { double a;double b;double c; sanjiaoxing(double _a,double _b,double _c) { a=_a; b=_b; c=_c; } public void zhouchang() { double d=a+b+c; System.out.println("三角形的周长="+d); } public void mianji() { double area; double s=(a+b+c)/2; area=(int)Math.sqrt(s*(s-a)*(s-b)*(s-c)); System.out.println("三角形的面积="+area); } } class juxing implements Shape{ double e;double f; juxing(double _e,double _f) { e=_e; f=_f; } public void zhouchang() { double g=e+f; System.out.println("矩形的周长="+g); } public void mianji() { double area=e*f; System.out.println("矩形的面积="+area); } } class yuan implements Shape{ double radious; yuan(double _radious){ radious= _radious; } public void zhouchang() { double h=2*3*radious; System.out.println("圆形的周长="+h); } public void mianji() { double area=3*radious*radious; System.out.println("圆形的面积="+area); } } public class Jiekoutest{ public static void main(String[] args) { Shape sanjiaoxing= new sanjiaoxing(3,4,5); Shape jixing= new juxing(6,7); Shape yuan= new yuan(2); sanjiaoxing.zhouchang(); sanjiaoxing.mianji(); juxing.zhouchang(); juxing.mianji(); yuan.zhouchang(); yuan.mianji(); } }

这段代码有两个错误：

1. 在 sanjiaoxing 类的 mianji 方法中，计算三角形面积的公式有误，应该使用海伦公式：

double s = (a + b + c) / 2;
double area = Math.sqrt(s * (s - a) * (s - b) * (s - c));

2. 在 main 方法中，jixing 变量的类型应该是 juxing，而不是 Shape。

以下是修改后的代码：

interface Shape {
    void zhouchang();
    void mianji();
}

class sanjiaoxing implements Shape {
    double a;
    double b;
    double c;

    sanjiaoxing(double _a, double _b, double _c) {
        a = _a;
        b = _b;
        c = _c;
    }

    public void zhouchang() {
        double d = a + b + c;
        System.out.println("三角形的周长=" + d);
    }

    public void mianji() {
        double s = (a + b + c) / 2;
        double area = Math.sqrt(s * (s - a) * (s - b) * (s - c));
        System.out.println("三角形的面积=" + area);
    }
}

class juxing implements Shape {
    double e;
    double f;

    juxing(double _e, double _f) {
        e = _e;
        f = _f;
    }

    public void zhouchang() {
        double g = 2 * (e + f);
        System.out.println("矩形的周长=" + g);
    }

    public void mianji() {
        double area = e * f;
        System.out.println("矩形的面积=" + area);
    }
}

class yuan implements Shape {
    double radious;

    yuan(double _radious) {
        radious = _radious;
    }

    public void zhouchang() {
        double h = 2 * Math.PI * radious;
        System.out.println("圆形的周长=" + h);
    }

    public void mianji() {
        double area = Math.PI * radious * radious;
        System.out.println("圆形的面积=" + area);
    }
}

public class Jiekoutest {
    public static void main(String[] args) {
        Shape sanjiaoxing = new sanjiaoxing(3, 4, 5);
        Shape juxing = new juxing(6, 7);
        Shape yuan = new yuan(2);

        sanjiaoxing.zhouchang();
        sanjiaoxing.mianji();
        juxing.zhouchang();
        juxing.mianji();
        yuan.zhouchang();
        yuan.mianji();
    }
}

注意，这里假设圆形的周长和面积使用的是数学常数 pi 的值，而不是 3。