抽象类的概念Java类的创建

抽象类的概念：通过创建抽象类形状Shape,分别计算圆、长方形、三角形的面积和周长：Shape类中定义将来子类可能会用到的属性和三个重载的构造方法以及求周长getper()和求面积area()的抽象方法。分别创建圆、长方形、三角形继承抽象类，实现求周长和求面积的计算。在主类中分别计算圆、长方形、三角形的面积和周长。
t = (a+b+c)/2.0;
double s = Math.sqrt(t*(t-a)(t-b)(t-c));

public abstract class Shape {

    protected List<Double> lengthList = new ArrayList<>();

    public Shape(double length) {
        lengthList.add(length);
    }

    public Shape(double length1, double length2) {
        lengthList.add(length1);
        lengthList.add(length2);
    }

    public Shape(double length1, double length2, double... more) {
        lengthList.add(length1);
        lengthList.add(length2);
        if (more != null) {
            for (double length : more) {
                lengthList.add(length);
            }
        }
    }

    /**
     * 计算周长
     *
     * @return
     */
    public abstract double getper();

    /**
     * 计算面积
     *
     * @return
     */
    public abstract double area();


}

public class Circle extends Shape {

    public Circle(double radius) {
        super(radius);
    }

    @Override
    public double getper() {
        return 2 * Math.PI * this.lengthList.get(0);
    }

    @Override
    public double area() {
        return Math.PI * this.lengthList.get(0) * this.lengthList.get(0);
    }
}

public class Rectangle extends Shape {

    public Rectangle(double length, double width) {
        super(length, width);
    }

    @Override
    public double getper() {
        return (this.lengthList.get(0) + this.lengthList.get(1)) * 2;
    }

    @Override
    public double area() {
        return this.lengthList.get(0) * this.lengthList.get(1);
    }

}

public class Triangle extends Shape {

    public Triangle(double length1, double length2, double length3) {
        super(length1, length2, length3);
    }

    @Override
    public double getper() {
        return this.lengthList.get(0) + this.lengthList.get(1) + this.lengthList.get(2);
    }

    @Override
    public double area() {
        Double a = this.lengthList.get(0);
        Double b = this.lengthList.get(1);
        Double c = this.lengthList.get(2);

        double t = (a + b + c) / 2.0;
        double s = Math.sqrt(t * (t - a) * (t - b) * (t - c));
        return s;
    }
}


public class Main {

    public static void main(String[] args) {
        Circle circle = new Circle(1);
        System.out.printf("圆形周长:%s,面积：%s\n", circle.getper(), circle.area());

        Rectangle rectangle = new Rectangle(3, 4);
        System.out.printf("长方形周长:%s,面积：%s\n", rectangle.getper(), rectangle.area());

        Triangle triangle = new Triangle(3, 4, 5);
        System.out.printf("三角形周长:%s,面积：%s\n", triangle.getper(), triangle.area());
    }
}

输出如下:

圆形周长:6.283185307179586,面积：3.141592653589793
长方形周长:14.0,面积：12.0
三角形周长:12.0,面积：6.0

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