JAVA学习笔记

Rectangle.java

class Rectangle extends Shape{//class 子类 extends 父类
double area(){ // 计算矩形面积的功能。
	 double a = super.getHeight();//get用来赋值，set用来获取值
	 double b = super.getWidth();
	 //super.(A)  super可以访问父类的①构造方法；②成员变量；③成员方法
	 return a * b;    
    }
}

Shape.java

public class Shape { //目标父类
    private double height; //高
    private double width; // 底边
	//构造
    public double getHeight() {
        return height;
    }
    public void setHeight(double height) {
        this.height = height;
    }

    public double getWidth() {
        return width;
    }
    public void setWidth(double width) {
        this.width = width;
    }
}

Triangle.java

// 定义一个Triangle的公开类，并继承Shape类
class Triangle extends Shape{
double area(){
    double a = super.getHeight();
    double b = super.getWidth();
    return 0.5*a * b;
    
    }
}

Test.java

public class Test {
    public static void main(String[] args) {
        Rectangle rectangle = new Rectangle();//构造
        rectangle.setHeight(30);//赋值
        rectangle.setWidth(20);
        Triangle triangle = new Triangle();
        triangle.setHeight(10);
        triangle.setWidth(15);
        System.out.printf("矩形的面积：%.2fn三角形的面积为%.2f",rectangle.area(),triangle.area());
    }
}

Demo(小样例)

public class Demo {
    public static void main(String[] args) {
        Sphere sphere = new Sphere(20.0);
        double s = sphere.area();
        System.out.printf("球的表面积为：%.2f", s);
    }
}

Sphere

class Shape {
    private double r; //球的半径
    // 球的体积3/4*π*r^3
    public double area(){
        double s = (double)3/4*Math.PI*Math.pow(r,3);
        return s;
    }
}
public class Sphere extends Shape{

    private double r; //球的半径
    public Sphere(double r) {//有参构造
        this.r = r;
    }
    // 重写 Shape 中的 area 方法，计算球的表面积（4πr^2），将计算结果返回
    public double area(){
        double s = (double)4 * Math.PI * Math.pow(r, 2);
        //Math.pow(a, b) 表示次方 a^b
        return s;
    }
}

Demo

public class Demo {
    public static void main(String[] args) {
        Seal seal = new Seal(0.7, 32.00);
        System.out.println("商品打折后的价格为："+seal.sealX());
        System.out.println("商品原来的价格为："+seal.getTotalMoney());
    }
}

seal

class Total {
    double totalMoney = 50.00;
    public double getTotalMoney(){
        return totalMoney;
    }
}
// 定义一个Seal的公开类，并继承Total类
public class Seal extends Total{
    double discount;//折扣
    double totalMoney;//总价格
    public Seal(double discount, double totalMoney){//有参构造
        this.discount=discount;
        this.totalMoney=totalMoney;
    }
    public double sealX(){//计算打折后的商品价格并返回
        return totalMoney*discount;
    }
}