题目：计算各种图形的周长和面积(圆,平行四边形,长方形,梯形)

package com.a4_22;

/**
 * Created by HongWeiPC on 2017/5/2.
 */
public interface Calculate {
    double area();
    double perimeter();
    void show();
}

class Circle implements Calculate {
    private int r;

    public Circle(int r){
        this.r=r;
    }
    @Override
    public double area() {
        return Math.PI * r * r;
    }

    @Override
    public double perimeter() {
        return 2 * Math.PI * r;
    }

    @Override
    public void show() {
        System.out.println("圆面积是"+this.area());
        System.out.println("圆周长是"+this.perimeter());
    }
}

class Parallelogram implements Calculate {
    private int a, h, b; //a是底边，b是斜边，h是高

    public Parallelogram(int a, int b, int h) {
        this.a = a;
        this.b = b;
        this.h = h;
    }

    @Override
    public double area() {
        return a * h;
    }

    @Override
    public double perimeter() {
        return 2 * (a + b);
    }
    public void show() {
        System.out.println("\n平行四边形面积是"+this.area());
        System.out.println("平行四边形周长是"+this.perimeter());
    }
}

class Rectangle implements Calculate {
    private double a, b;
    public Rectangle(double a,double b){
        this.a=a;
        this.b=b;
    }

    @Override
    public double area() {
        return a * b;
    }

    @Override
    public double perimeter() {
        return 2 * (a + b);
    }

    @Override
    public void show() {
        System.out.println("\n矩形面积是"+this.area());
        System.out.println("矩形周长是"+this.perimeter());
    }
}

class Trapezoid implements Calculate {
    private double ul, dl, h; //ul是上边长，dl是下边长，h是高
    private double x1,x2; //x1是斜边1，x2是斜边2
    public Trapezoid(double ul,double dl,double h,double x1,double x2){
        this.ul=ul; this.dl=dl; this.h=h; this.x1=x1; this.x2=x2;
    }
    @Override
    public double area() {
        return ((ul + dl) * h) / 2;
    }

    @Override
    public double perimeter() {
        return ul+dl+h+x1+x2;
    }
    public void show() {
        System.out.println("\n梯形面积是"+this.area());
        System.out.println("梯形周长是"+this.perimeter());
    }
}

class TestCalculate{
    public static void main(String[] args) {
        Circle c1 = new Circle(5);
        Parallelogram p1 = new Parallelogram(3,4,6);
        Rectangle r1=new Rectangle(2,3);
        Trapezoid t1=new Trapezoid(3,5,2,3,4);
        c1.show();
        p1.show();
        r1.show();
        t1.show();
    }

}

运行图