请用接口实现以下UML图 ，Java程序：使用匿名类实现，有三个柱体，分别以三角形，圆形，矩形为底面积，求它们的体积。 测试用例：:三角形边：（3，4，5）;圆形半径：2; 矩形边（3，4），柱体高：6.

//定义接口Geometry
interface Geometry {
    double getArea();
}

//定义三角形类Triangle，实现Geometry接口
class Triangle implements Geometry {
    double a, b, c;
    Triangle(double a, double b, double c) {
        this.a = a;
        this.b = b;
        this.c = c;
    }
    public double getArea() {
        double p = (a + b + c) / 2;
        return Math.sqrt(p * (p - a) * (p - b) * (p - c));
    }
}

//定义圆形类Circle，实现Geometry接口
class Circle implements Geometry {
    double r;
    Circle(double r) {
        this.r = r;
    }
    public double getArea() {
        return Math.PI * r * r;
    }
}

//定义矩形类Rectangle，实现Geometry接口
class Rectangle implements Geometry {
    double a, b;
    Rectangle(double a, double b) {
        this.a = a;
        this.b = b;
    }
    public double getArea() {
        return a * b;
    }
}

//定义柱体类Pillar
class Pillar {
    double height;
    Geometry bottom;
    Pillar(Geometry bottom, double height) {
        this.bottom = bottom;
        this.height = height;
    }
    public double getVolume() {
        return bottom.getArea() * height;
    }
}

public class Main {
    public static void main(String[] args) {
        //创建三角形、圆形、矩形对象
        Geometry triangle = new Triangle(3, 4, 5);
        Geometry circle = new Circle(2);
        Geometry rectangle = new Rectangle(3, 4);

        //创建三个柱体对象
        Pillar pillar1 = new Pillar(triangle, 6);
        Pillar pillar2 = new Pillar(circle, 6);
        Pillar pillar3 = new Pillar(rectangle, 6);

        //输出三个柱体的体积
        System.out.println("三角形底的柱体体积为：" + pillar1.getVolume());
        System.out.println("圆形底的柱体体积为：" + pillar2.getVolume());
        System.out.println("矩形底的柱体体积为：" + pillar3.getVolume());
    }
}

--相关问题--:
1. 什么是接口？接口和抽象类有什么