多种方法实现单例模式

package cn.singleton;

import java.util.HashMap;
import java.util.Map;

/**
?* 单例模式实现
?* @author 姚伟楠
?*
?*/
public class Singleton {

?/**
? * 测试入口
? * @param args
? */
?public static void main(String[] args) {
??// TODO Auto-generated method stub
??Object obj1=Object.getInstance();
??Object obj2=Object.getInstance();
??System.out.print("懒汉式：");
??System.out.println(obj1==obj2);
??Object1 obj3=Object1.getInstance();
??Object1 obj4=Object1.getInstance();
??System.out.print("饿汉式：");
??System.out.println(obj3==obj4);
??Object2 obj5=Object2.getInstance(Object2.class.getName());
??Object2 obj6=Object2.getInstance(Object2.class.getName());
??System.out.print("登记式：");
??System.out.println(obj5==obj6);
??
?}

}
/**
?* 懒汉式单例(需要时候才实例化)
?* @author 姚伟楠
?*
?*/
class Object{
?private static Object instance=null;
?private Object() {}
?public static synchronized Object getInstance(){
??if(null==instance)instance=new Object();
??return instance;
??
?}
}
/**
?* 饿汉式(初始化类时候实例化)
?* @author 姚伟楠
?*
?*/
class Object1{
?private static Object1 instance=new Object1();
?private Object1(){}
?public static Object1 getInstance(){
??return instance;
?}
}
/**
?* 登记式(内类存储实例并作登记,需要时直接按照登记号（类名）获取)
?* @author 姚伟楠
?*
?*/
class Object2{
?private static Map<String, Object2> instances=new HashMap<String, Object2>();
?static{
??Object2 instance=new Object2();
??instances.put(Object2.class.getName(), instance);
?}
?/**
? * 保证子类、同包、自身可以创建非单例实例
? */
?protected Object2(){}
?public static Object2 getInstance(String name){
??if(null==name){
???name = Object2.class.getName();
??}
?? if(instances.get(name) == null) {
???????????? try {
???????????? ?instances.put(name, (Object2) Class.forName(name).newInstance());
???????????? } catch (InstantiationException e) {
???????????????? e.printStackTrace();
???????????? } catch (IllegalAccessException e) {
???????????????? e.printStackTrace();
???????????? } catch (ClassNotFoundException e) {
???????????????? e.printStackTrace();
???????????? }
???????? }

??return instances.get(name);
??
?}
}