extends作业三

public class 测试 {    public static void main(String[] args) {        Rectangle r=new Rectangle(3,4);        System.out.println("长=4，宽=3的矩形周长="+r.perimeter());        Triangle t=new Triangle();        System.out.println( "边分别是3,4,5的三边形周长是：");        t.perimeter(3, 4, 5);           }}

public class Rectangle extends Shape {    private double a;    private double b;    public Rectangle( double a, double b) {        super();        this.a = a;        this.b = b;         }    @Override    public double perimeter(){        double perimeter;        perimeter=(a+b)*2;        return perimeter;    }    public double area(){        double area;        area=a*b;        return area;    }}

public class Shape {    private double perimeter;    private double area;    public Shape(double perimeter, double area) {        super();        this.perimeter = perimeter;        this.area = area;       }    public Shape() {        super();    }    //抽象一个周长方法     public  double perimeter(){        return perimeter;        }    //抽象一个面积方法     public  double area(){            return area;        }    }

public class Triangle extends Shape {    private double b;    private double c;    private double d;    public Triangle( double b, double c, double d) {        super();        this.b = b;        this.c = c;        this.d = d;    }    public Triangle() {    }    //周长     public void     perimeter (double b,double c,double d) {         if(b+c>d&&(b-c)<d) {             double perimeter ;             System.out.println(perimeter =b+c+d);               }else {            System.out.println("这不是三角形");           }             }}