Java编译器无法识别派生类，即 "symbol not found"错误

Question

当我尝试编译此代码时，出现“找不到符号”错误。总的来说，我可以创建 Ball 类型的对象，没有问题，但如果我尝试创建篮球类型的对象，编译器会提示。我对java很陌生，请帮忙吗？

class Ball {
    public double radious;
    public String color;

    Ball( double radious, String color ) {
        this.radious = radious;
        this.color = color;
    }

    public double area() {
        return (4 * Math.pow(this.radious, 2) * Math.PI );
    }

    public void display() {
            System.out.println("\nRadious: " + radious );
            System.out.println("Color: " + color );
    }

    class Basketball extends Ball {
        public int noOfStripes;

        Basketball( int n, double r, String c ) {
            super( r, c );
            noOfStripes = n;
        }

        Basketball( double r, String c ) {
            super( r, c );
            noOfStripes = 8; // Default value 
        }

        public void display() {
            super.display();
            System.out.println("Area: " + area() );
            System.out.println("noOfStripes: " + noOfStripes );
        }
    }
}

class Driver {
    public static void main( String[] args ) {
        Ball basket1 = new Ball( 29.5, "Orange" );
        basket1.display();

        Ball basket2 =new Basketball( 29.5, "Black" );
    }
}

Answer 1

您不仅创建了 Basketball 作为 Ball 的子类，而且还创建了一个内部类。它不需要是内部类。

在 Ball 类的大括号之外定义 Basketball。

    }
}  // End of Ball class

class Basketball extends Ball
{
   // ...