单例模式(3.注册式)

package test;

import java.util.HashMap;

public class RegSingleton {

 private static HashMap m_registry = new HashMap();

 static {
  RegSingleton x = new RegSingleton();
  m_registry.put(x.getClass().getName(), x);
 }

 // 注意该构造器不能是私有的，子类构造器需要调用
 public RegSingleton() {
 }

 public static RegSingleton getInstance(String name) {
  if (name == null) {
   name = "test.RegSingleton";
  }
  if (m_registry.get(name) == null) {
   try {
    m_registry.put(name, Class.forName(name).newInstance());
   } catch (Exception e) {
    System.out.println("Error happened.");
   }
  }
  return (RegSingleton) (m_registry.get(name));
 }
}

 

package test;

public class RegSingletonChild extends RegSingleton {
 /**
  * 构造器不能为private,父类getInstance方法需要调用该构造器
  */
 public RegSingletonChild() {
 }

 /**
  * 静态工厂方法
  */
 public static RegSingletonChild getInstance() {
  return (RegSingletonChild) RegSingleton.getInstance("test.RegSingletonChild");
 }

 public String toString() {
  return "I am RegSingletonChild's instance.";
 }
}