一段抽象类的代码，类方法中报错，不知道哪有问题

This topic created in 2784 days ago, the information mentioned may be changed or developed.

package com.yau;

public abstract class Shape {

    public abstract void calArea();

    public abstract void calPerimeter();


    public class Rectangle extends Shape {
        public double h;
        public double w;

        public Rectangle(double h, double w) {
            this.h = h;
            this.w = w;
        }

        public void calArea() {
            System.out.println("Rectangle's area:" + h * w);
        }

        public void calPerimeter() {
            System.out.println("Rectangle's perimeter" + 2 * (h + w));
        }
    }

    public class Circle extends Shape {
        public double r;

        public Circle(double r) {
            this.r = r;
        }

        public void calArea() {
            System.out.println("Circle's area:" + r * r * Math.PI);
        }

        public void calPerimeter() {
            System.out.println("Circle's perimeter:" + 2 * r * Math.PI);
        }
    }

    public static void main(String[] args) {
        Shape s1 = new Rectangle(8.2,2.8);     //此处报错
        s1.calArea();
        s1.calPerimeter();
        Shape s2 = new Circle(9.39);           //此处报错
        s2.calArea();
        s2.calPerimeter();

    }
}

public

void

shape

double

4 replies • 2018-10-22 15:51:45 +08:00

JohnZorn

Oct 22, 2018

main 是静态方法非静态的东西拿到静态能直接用？要么静态内部类要么 main 构造实例

huangzhe8263

Oct 22, 2018 via Android

好消息好消息
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TommyLemon

Oct 22, 2018

目测是声明与引用顺序的问题，把 Rectangle 和 Circle 分别单独写成一个文件试试

quinoa42

Oct 22, 2018

```
Temp.java:43: error: non-static variable this cannot be referenced from a static context
Shape s1 = new Rectangle(8.2,2.8); //此处报错
^
Temp.java:46: error: non-static variable this cannot be referenced from a static context
Shape s2 = new Circle(9.39); //此处报错
```
javac 不是都报了吗……
简单的说，你的 rectangle 和 circle 是 inner class，关联的是单独的一个 shape instance 而不是 shape class
要过编译的话在 rectangle 和 circle 的声明行加上 static