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【第15章：Java反射机制】_工厂设计模式

发布时间：2021-01-07 18:13:12编辑：雪饮阅读（）

 一个简单的工厂设计模式

package org.kasumi;
interface Fruit{
       public void eat();
}
class Apple implements Fruit{
       public void eat(){
              System.out.println("苹果");
       }
}
class Orange implements Fruit{
       public void eat(){
              System.out.println("橙子");
       }
}
class Factory{
       public static Fruit getInstance(String className){
              Fruit fruit=null;
              if("apple".equals(className)){
                     fruit=new Apple();
              }
              if("orange".equals(className)){
                     fruit=new Orange();
              }
              return fruit;
       }
}
public class Hello{
   public static void main(String args[]){
              Fruit f=Factory.getInstance("apple");
              if(f!=null){
                     f.eat();
              }
       }
};

缺点：这种工厂设计模式，如果要有新的类型需要工厂类来生产其实例，则需要重新修改下工厂类
用反射实现工厂设计模式
package org.kasumi;
interface Fruit{
       public void eat();
}
class Apple implements Fruit{
       public void eat(){
              System.out.println("苹果");
       }
}
class Orange implements Fruit{
       public void eat(){
              System.out.println("橙子");
       }
}
class Factory{
       public static Fruit getInstance(String className){
              Fruit fruit = null ;
              try{
                     fruit = (Fruit)Class.forName(className).newInstance() ;
              }catch(Exception e){
                     e.printStackTrace() ;
              }
              return fruit ;
       }
}
public class Hello{
   public static void main(String args[]){
              Fruit f = Factory.getInstance("org.kasumi.Apple") ;
              if(f!=null){
                     f.eat() ;
              }
       }
};
D:\>javac -d . Hello.java
D:\>java org.kasumi.Hello
苹果
利用反射实现的工厂设计模式，若有新类则工厂类无需变动代码
不足：有新类时候要在调用处修改新类的以包为基的路径指向，若能直接做成配置文件就更好了。
用配置文件决定工厂模式工厂类的对象实例生产
package org.kasumi;
import java.util.Properties ;
import java.io.File ;
import java.io.FileOutputStream ;
import java.io.FileInputStream ;
interface Fruit{
       public void eat();
}
class Apple implements Fruit{
       public void eat(){
              System.out.println("苹果");
       }
}
class Orange implements Fruit{
       public void eat(){
              System.out.println("橙子");
       }
}
class Init{
       public static Properties getPro(){
              Properties pro = new Properties() ;
              File f = new File("d:\\fruit.properties") ;      // 找到属性文件
              try{
                     if(f.exists()){     // 文件存在
                            pro.load(new FileInputStream(f)) ;      // 读取属性
                     }else{
                            pro.setProperty("apple","org.kasumi.Apple") ;
                            pro.setProperty("orange","org.kasumi.Orange") ;
                            pro.store(new FileOutputStream(f),"FRUIT CLASS") ;
                     }
              }catch(Exception e){}
              return pro ;
       }
};
class Factory{
       public static Fruit getInstance(String className){
              Fruit fruit = null ;
              try{
                     fruit = (Fruit)Class.forName(className).newInstance() ;
              }catch(Exception e){
                     e.printStackTrace() ;
              }
              return fruit ;
       }
}
public class Hello{
   public static void main(String args[]){
              Properties pro = Init.getPro() ;
              Fruit f = Factory.getInstance(pro.getProperty("apple")) ;
              if(f!=null){
                     f.eat() ;
              }
       }
};
D:\>javac -d . Hello.java
D:\>java org.kasumi.Hello
苹果