Cylinder c2=new Cylinder(9,4);以上语句在报错，怎么改正呢?(语言-java)

Question

public class Circle{ double radius; public Circle(int r){
radius=r;}
public double getArea() { return Math.PI*radius*radius; }
public double getPre() { return Math.PI*radius*2; }
public class Cylinder{ Circle c; int h; Cylinder(int h1,int r1){
h=h1;
c=new Circle(r1);
} public double getArea(){
return c.getArea()*2+c.getArea()*h;} public double getVol(){
return c.getArea()*h;}`

   }`
    public static void main(String[]args) `{
        Circle c1=new Circle(4);
        c1.getArea();
        c1.getPre();
        Cylinder c2=new Cylinder(9,4);
        c2.getArea();
        c2.getVol(); 
        System.out.println("圆的面积="+c1.getArea());
        System.out.println("圆的周长="+c1.getPre());
        System.out.println("圆柱表面积="+c2.getArea());
        System.out.println("圆柱体积="+c2.getVol());
}`
       }`

Answer 1

• 对象的组合：

public class Circle {
    double radius;

    public Circle(int r) {
        radius = r;
    }

    public double getArea() {
        return Math.PI * radius * radius;
    }

    public double getPre() {
        return Math.PI * radius * 2;
    }

    public static void main(String[] args) {
        Circle c1 = new Circle(4);
        c1.getArea();
        c1.getPre();
        Cylinder c2 = new Cylinder(9, 4);
        c2.getArea();
        c2.getVol();
        System.out.println("圆的面积=" + c1.getArea());
        System.out.println("圆的周长=" + c1.getPre());
        System.out.println("圆柱表面积=" + c2.getArea());
        System.out.println("圆柱体积=" + c2.getVol());
    }
}

class Cylinder {
    Circle c;
    int h;

    Cylinder(int h1, int r1) {
        h = h1;
        c = new Circle(r1);
    }

    public double getArea() {
        return c.getArea() * 2 + c.getArea() * h;
    }

    public double getVol() {
        return c.getArea() * h;
    }

}

• 继承

public class Circle {
    double radius;

    public Circle(int r) {
        radius = r;
    }

    public double getArea() {
        return Math.PI * radius * radius;
    }

    public double getPre() {
        return Math.PI * radius * 2;
    }

    public static void main(String[] args) {
        Circle c1 = new Circle(4);
        c1.getArea();
        c1.getPre();
        Cylinder c2 = new Cylinder(9, 4);
        c2.getArea();
        c2.getVol();
        System.out.println("圆的面积=" + c1.getArea());
        System.out.println("圆的周长=" + c1.getPre());
        System.out.println("圆柱表面积=" + c2.getArea());
        System.out.println("圆柱体积=" + c2.getVol());
    }
}

class Cylinder extends Circle{
    int h;

    Cylinder(int h1, int r1) {
        super(r1);
        h = h1;
    }

    public double getArea() {
        return super.getArea() * 2 + super.getArea() * h;
    }

    public double getVol() {
        return super.getArea() * h;
    }

}