import java.util.*;
import java.io.*;
public class ObjectPoolFactory
{
  // 定義一個(gè)對(duì)象池,前面是對(duì)象名，后面是實(shí)際對(duì)象
  private Map<String ,Object> objectPool = new HashMap<>();
  // 定義一個(gè)創(chuàng)建對(duì)象的方法，
  // 該方法只要傳入一個(gè)字符串類名，程序可以根據(jù)該類名生成Java對(duì)象
  private Object createObject(String clazzName)
     throws InstantiationException
     , IllegalAccessException , ClassNotFoundException
  {
   // 根據(jù)字符串來獲取對(duì)應(yīng)的Class對(duì)象
   Class<?> clazz = Class.forName(clazzName);
   // 使用clazz對(duì)應(yīng)類的默認(rèn)構(gòu)造器創(chuàng)建實(shí)例
   return clazz.newInstance();
  }
  // 該方法根據(jù)指定文件來初始化對(duì)象池，
  // 它會(huì)根據(jù)配置文件來創(chuàng)建對(duì)象
  public void initPool(String fileName)
     throws InstantiationException
     , IllegalAccessException ,ClassNotFoundException
  {
   try(
      FileInputStream fis = new FileInputStream(fileName))
   {
     Properties props = new Properties();
     props.load(fis);
     for (String name : props.stringPropertyNames())
     {
      // 每取出一對(duì)key-value對(duì)，就根據(jù)value創(chuàng)建一個(gè)對(duì)象
      // 調(diào)用createObject()創(chuàng)建對(duì)象，并將對(duì)象添加到對(duì)象池中
      objectPool.put(name ,
         createObject(props.getProperty(name)));
     }
   }
   catch (IOException ex)
   {
     System.out.println("讀取" + fileName + "異常");
   }
  }
  public Object getObject(String name)
  {
   // 從objectPool中取出指定name對(duì)應(yīng)的對(duì)象。
   return objectPool.get(name);
  }
  public static void main(String[] args)
     throws Exception
  {
   ObjectPoolFactory pf = new ObjectPoolFactory();
   pf.initPool("obj.txt");
   System.out.println(pf.getObject("a"));   // ①
   System.out.println(pf.getObject("b"));   // ②
  }
}

a=java.util.Date
b=javax.swing.JFrame

import java.lang.reflect.*;
public class CreateJFrame
{
  public static void main(String[] args)
     throws Exception
  {
   // 獲取JFrame對(duì)應(yīng)的Class對(duì)象
   Class<?> jframeClazz = Class.forName("javax.swing.JFrame");
   // 獲取JFrame中帶一個(gè)字符串參數(shù)的構(gòu)造器
   Constructor ctor = jframeClazz
      .getConstructor(String.class);
   // 調(diào)用Constructor的newInstance方法創(chuàng)建對(duì)象
   Object obj = ctor.newInstance("測(cè)試窗口");
   // 輸出JFrame對(duì)象
   System.out.println(obj);
  }
}