java抽象类：[1]抽象类shape

java中抽象类作用：通过继承它实现多态，后期绑定，可以为将来要实现的东西做好接口，实现重用性。要如何使用呢，接下来我们来简单实现一下例：定义一个抽象类shape,他包含一个抽象方法getArea(),从shape类派生出Rectang和circle类，这两个类都用getArea（）方法计算对象的面积首先写一个抽象类shape,他包含一个抽象方法getArea()从shape类派生出rectang类，并用了getArea()计算矩形的面积从shape类派生出circle类，并用了getArea()计算圆的面积实例化对象，并调用方法结果以下为完整代码public class demo3 {public static void main(String[] args) {rectang rec=new rectang(3,5);System.out.println("Area for Circle with width=3 and height=5 is:"+rec.getArea());circle cir=new circle(2);System.out.println("Area for Circle with r=2 is:"+cir.getArea()); }}abstract class shape{public abstract double getArea();} class rectang extends shape{private double width;private double height;public rectang(double width,double height){this.width=width;this.height=height;}public double getArea(){return width*height;}}class circle extends shape{private double r;public circle(double radius){this.r=radius;}public double getArea(){return Math.PI*r*r;}}