前言

涉及知识点

• 1.对于创建对象和类的初步实践；
  如构建圆类和矩形类；
• 1.对于抽象类和继承与多态的认识；
  如构建shape类；

题量

• 不多，可以完成。

难度

• 不大，可以完成。

设计与分析

题目源码如下

import java.util.*;

public class Main {
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        Scanner input = new Scanner(System.in);

        int choice = input.nextInt();

        switch (choice) {
            case 1://Circle
                double r = input.nextDouble();
                Shape circle = new Circle(r);
                circle.getArea();
                break;
            case 2://Rectangle
                double x1 = input.nextDouble();
                double y1 = input.nextDouble();
                double x2 = input.nextDouble();
                double y2 = input.nextDouble();

                Point leftTopPoint = new Point(x1, y1);
                Point lowerRightPoint = new Point(x2, y2);

                Rectangle rectangle = new Rectangle(leftTopPoint, lowerRightPoint);
                rectangle.getArea();
                break;
        }

    }
}

public abstract class Shape {


    public abstract void getArea();
}
```plaintext
public class Circle extends Shape {
    double r;

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

    @Override
    public void getArea(){
        double s = (3.1415926)*r*r;
        System.out.printf("%.2f",s);
    }
}

public class Rectangle extends Shape {

    private Point topLeftPoint;
    private Point lowerRightPoint;

    public Rectangle(Point topLeftPoint,Point lowerRightPoint){
        this.lowerRightPoint=lowerRightPoint;
        this.topLeftPoint=topLeftPoint;
    }
    @Override
    public void getArea(){
        double s=(topLeftPoint.getX() - lowerRightPoint.getX())*(topLeftPoint.getY()- lowerRightPoint.getY());
        if(s<0){
            s=-s;
        }
        System.out.printf("%.2f",s);
    }



}

public class Point {
        private double x;
        private double y;

        public Point(){

        }

        public Point(double x,double y){
            this.x=x;
            this.y=y;
        }

        public double getX() {
            return x;
        }

        public double getY() {
            return y;
        }
    }

踩坑心得

1.implements实现并不熟悉;

改进建议

1.多加练习;

总结

我学到了很多关于类的基本使用、抽象类的创建及使用、继承和多态的性质等知识，但是对于接口实现还是不够熟练，日后需要多多练习;