题目：
利用接口和接口回调，实现简单工厂模式，当输入不同的字符，代表相应图形时，利用工厂类获得图形对象，再计算以该图形为底的柱体体积。
代码：
1、Test.java
1 /**
2 * 测试类
3 * 求体积;
4 */
5 package cn.edu.ccut;
6
7 import java.util.Scanner;
8 public class Test {
9
10 public static void main(String[] args) {
12 while(true){
13 System.out.println("柱体底的形状:");
14 Scanner reader = new Scanner(System.in);
15 char c = reader.next().charAt(0);
20 Factory f = new Factory();
21 Cone cone = new Cone(f.get(c) , 6);
22 System.out.println("体积: "+cone.getV());
23 }
24 }
25
26 }
2、Factory.java
1 /**
2 * 工厂类
3 * get返回用户所需对象;
4 */
5 package cn.edu.ccut;
6
7 public class Factory {
8 Shape shape = null;
8
9 public Shape get(char c){
10 switch(c){
11 case 'j':shape = new Rec(3,5);break;
12 case 's':shape = new Triangle(3,4,5);break;
13
14 case 't':shape = new Trapezoid(4,5,7);break;
15 case 'y':shape = new Circle(3);break;
16 default:System.out.println("wrong");
17 }
18 return shape;
19 }
20 }
3、Shape.java
1 /**
2 * 图形接口;
4 */
5 package cn.edu.ccut;
6
7 public interface Shape {
8 public double getArea();
9 }
4、Rec.java
1 /**
2 * 实现了图形接口的矩形类包含两个成员变量并实现了getArea方法;
3 * 成员变量代表的长和宽;
5 */
6 package cn.edu.ccut;
7
8 public class Rec implements Shape {
9 double a;
10 double b;
10
11 Rec(double a , double b){
12 this.a = a;
13 this.b = b;
14 }
15 public double getArea(){
16 return (a*b);
17 }
18 }
5、Circle.java
1 /**
2 * 实现了图形接口的圆类一个成员变量,两个方法;
3 * 成员变量r为半径;
4 *
5 */
6 package cn.edu.ccut;
7
8 public class Circle implements Shape{
9 double r;
10
11 public Circle(double r){
12 this.r = r;
13 }
14 public double getArea(){
15 return (Math.PI*r*r);
16 }
17 }
6、Triangle.java
1 /**
2 * 三角形类三个成员变量,两个方法;
3 * 成员变量a,b,c代表三个边;
4 *
5 */
6 package cn.edu.ccut;
7
8 public class Triangle implements Shape{
9 double a;
10 double b;
11 double c;
12
13 public Triangle (double a , double b , double c){
14 this.a = a;
15 this.b = b;
16 this.c = c;
17 }
18 public double getArea(){
19 double p = (a + b + c) / 2;
20 return Math.sqrt(p * (p - a) * (p - b) * (p - c));
21 }
22 }
7、Trapezoid.java
1 /**
2 * 梯形类包含三个成员变量,两个方法;
3 * a,b代表上底和下底,height代表高;
4 *
5 */
6 package cn.edu.ccut;
7
8 public class Trapezoid implements Shape{
9 double a;
10 double b;
11 double height;
12
13 public Trapezoid(double a , double b , double height){
14 this.a = a;
15 this.b = b;
16 this.height = height;
17 }
18 public double getArea(){
19 return (((a + b) * height) / 2);
20 }
21 }
8、Cone.java
1 /**
2 * 柱体类两个成员变量,三个方法;
3 * shape代表底,height代表高;
4 *
5 */
6 package cn.edu.ccut;
7
8 public class Cone {
9 Shape shape;
10 double height;
10
11 public Cone(Shape shape , double height){
12 this.shape = shape;
13 this.height = height;
14 }
15 public double getV(){
16 return (shape.getArea()*height);
17 }
18 public void setDi(Shape shape){
19 this.shape = shape;
20 }
21 }
运行结果：
