java抽象类用法

Question

嗨,我想在Eclipse中执行此代码.

abstract class ShapeNew {
    int length;
    public abstract double area();
}
 class Rect extends Shape{
    Rect(int side){
        this.length = side;
    }
    public double area(){
        System.out.println("area of rectangle"+ length*length);
        return length*length;
    }



    /**
     * @param args
     */
public static class Area{
    public static void main(String[] args) {
        // TODO Auto-generated method stub

        ShapeNew rect = new Rect(32);// I am unable to use this. The eclipse throws an error//

        rect.area();
    }

}

任何人都可以帮助我.为什么我无法将ShapeNew的引用分配给Rect的对象？我收到这个错误

Exception in thread "main" java.lang.Error: Unresolved compilation problem: 
    Type mismatch: cannot convert from Rect to ShapeNew

Answer 1

你有一个错字:你需要从你定义的类扩展:

class Rect extends ShapeNew {

(另外,看起来你已经实现了一个正方形而不是一个矩形,因为你的面积函数是一个长度).