代码错误import java.util.Scanner; public class Main{ public static void main (String args[]){ Shape s=new Oval(a,b); System.out.println("The area of "+s.toString()+" is "+s.area()); System.out.println("The perimeterof "+s.toString()+" is "+s.perimeter()); }} class Shape{ abstract double area(); abstract double perimeter(); } class Oval extends Shape{ private double a; //长轴半径 private double b; //短轴半径 Oval(double a,double b){ Scanner scanner = new Scanner(System.in); this.a= scanner.nextDouble(); this.b= scanner.nextDouble(); } Oval(){ this.a=0; this.b=0; } double area(){ return Math.PI*a*b; } double perimeter(){ return 2*Math.PI*b+4*(a-b); //L=2πb+4(a-b) } public String toString() { return "Oval(a:" + this.a + ",b:" + this.b + ")"; } }

这段代码有两个问题：

1. 在创建 Oval 对象时，应该将 main 函数中的 a 和 b 作为参数传递进去，而不是从控制台读取输入。因此，Shape s=new Oval(a,b); 应该改为 Shape s=new Oval(3, 4);（3 和 4 可以替换为任意值）

2. 在 Shape 类中的 abstract 方法需要添加 abstract 关键字，因为 Shape 类是一个抽象类。

修改后的代码如下：

import java.util.Scanner;

public class Main {
    public static void main(String args[]) {
        double a = 3; // 长轴半径
        double b = 4; // 短轴半径

        Shape s = new Oval(a, b);
        System.out.println("The area of " + s.toString() + " is " + s.area());
        System.out.println("The perimeter of " + s.toString() + " is " + s.perimeter());
    }
}

abstract class Shape {
    abstract double area();

    abstract double perimeter();
}

class Oval extends Shape {
    private double a; // 长轴半径
    private double b; // 短轴半径

    Oval(double a, double b) {
        this.a = a;
        this.b = b;
    }

    Oval() {
        this.a = 0;
        this.b = 0;
    }

    double area() {
        return Math.PI * a * b;
    }

    double perimeter() {
        return 2 * Math.PI * b + 4 * (a - b); // L=2πb+4(a-b)
    }

    public String toString() {
        return "Oval(a:" + this.a + ",b:" + this.b + ")";
    }
}