深入解析Java的设计模式编程中单例模式的使用

package com.wolf.action;
import java.util.HashMap;
import java.util.Map;
public class demo {
 public static void main(String args[]) throws InstantiationException,
  IllegalAccessException, ClassNotFoundException {
 System.out.println(Son.getInstance().getName());
 System.out.println("我是谁");
 }
}
class Son extends Father {
 private String name = "儿子";
 final String CLASS = "demo";
 protected String getName() {
 return this.query("aaa");
 }
 public static Son getInstance() throws InstantiationException,
  IllegalAccessException, ClassNotFoundException {
 // 这里必须是全局路径 否则无法找到
 return (Son) instance("com.wolf.action.Son");
 }
}
class Father {
 private static Map<String, Object> instance = new HashMap<String, Object>();
 private String name = "父类";
 protected void Fatcher() {
 System.out.println("我是父类");
 }
 protected String query(String sql) {
 return sql + "has been done";
 }
 public static Object instance(String objname)
  throws InstantiationException, IllegalAccessException,
  ClassNotFoundException {
 if (instance.get(objname) == null
  || !(instance.get(objname) instanceof Father)) {
  instance.put(objname, Class.forName(objname).newInstance());
 }
 return instance.get(objname);
 }
}

public class Singleton { 
  private static Singleton singleton = new Singleton(); 
  private Singleton(){} 
  public static Singleton getInstance(){ 
    return singleton; 
  } 
} 

public class Singleton { 
  private static Singleton singleton; 
  private Singleton(){} 
   
  public static synchronized Singleton getInstance(){ 
    if(singleton==null){ 
      singleton = new Singleton(); 
    } 
    return singleton; 
  } 
} 

Class c = Class.forName(Singleton.class.getName()); 
Constructor ct = c.getDeclaredConstructor(); 
ct.setAccessible(true); 
Singleton singleton = (Singleton)ct.newInstance();