class A(){private A(){}public name;pulbic static A creatInstance(){return new A();}}A a = A.createInstance();
a.name; //name 属性

public class single{ private static final single s=new single(); private single(){ } public static single getInstance(){ return s; }
}

public class Singleton {private static Singleton uniqueInstance = null;private Singleton() {// Exists only to defeat instantiation.
 }public static Singleton getInstance() {if (uniqueInstance == null) {uniqueInstance = new Singleton();}return uniqueInstance;}// Other methods...

}

public class TestStream {private String name;public String getName() {return name;}public void setName(String name) {this.name = name;} //该类只能有一个实例private TestStream(){}    //私有无参构造方法//该类必须自行创建//有2种方式/*private static final TestStream ts=new TestStream();*/private static TestStream ts1=null;//这个类必须自动向整个系统提供这个实例对象public static TestStream getTest(){if(ts1==null){ts1=new TestStream();}return ts1;}public void getInfo(){System.out.println("output message "+name);}}

public class TestMain {public static void main(String [] args){TestStream s=TestStream.getTest();s.setName("张孝祥");System.out.println(s.getName());TestStream s1=TestStream.getTest();s1.setName("张孝祥");System.out.println(s1.getName());s.getInfo();s1.getInfo();if(s==s1){System.out.println("创建的是同一个实例");}else if(s!=s1){System.out.println("创建的不是同一个实例");}else{System.out.println("application error");}}}

//饿汉式单例类.在类初始化时，已经自行实例化 public class Singleton1 {//私有的默认构造子private Singleton1() {}//已经自行实例化 private static final Singleton1 single = new Singleton1();//静态工厂方法 public static Singleton1 getInstance() {return single;}}

//懒汉式单例类.在第一次调用的时候实例化 public class Singleton2 {//私有的默认构造子private Singleton2() {}//注意，这里没有final    private static Singleton2 single=null;//静态工厂方法 public synchronized  static Singleton2 getInstance() {if (single == null) {  single = new Singleton2();}  return single;}}

import java.util.HashMap;import java.util.Map;//登记式单例类.//类似Spring里面的方法，将类名注册，下次从里面直接获取。public class Singleton3 {private static Map<String,Singleton3> map = new HashMap<String,Singleton3>();static{Singleton3 single = new Singleton3();map.put(single.getClass().getName(), single);}//保护的默认构造子protected Singleton3(){}//静态工厂方法,返还此类惟一的实例public static Singleton3 getInstance(String name) {if(name == null) {name = Singleton3.class.getName();System.out.println("name == null"+"--->name="+name);}if(map.get(name) == null) {try {map.put(name, (Singleton3) Class.forName(name).newInstance());} catch (InstantiationException e) {e.printStackTrace();} catch (IllegalAccessException e) {e.printStackTrace();} catch (ClassNotFoundException e) {e.printStackTrace();}}return map.get(name);}//一个示意性的商业方法public String about() {    return "Hello, I am RegSingleton.";    }    public static void main(String[] args) {Singleton3 single3 = Singleton3.getInstance(null);System.out.println(single3.about());}}

//单例对象的初始化同步
public class GlobalConfig {private static GlobalConfig instance = null;private Vector properties = null;private GlobalConfig() {//Load configuration information from DB or file//Set values for properties
    }private static synchronized void syncInit() {if (instance == null) {instance = new GlobalConfig();}}public static GlobalConfig getInstance() {if (instance == null) {syncInit();}return instance;}public Vector getProperties() {return properties;}}

public class GlobalConfig {private static GlobalConfig instance;private Vector properties = null;private boolean isUpdating = false;private int readCount = 0;private GlobalConfig() {//Load configuration information from DB or file//Set values for properties
 }private static synchronized void syncInit() {if (instance == null) {instance = new GlobalConfig();}}public static GlobalConfig getInstance() {if (instance==null) {syncInit();}return instance;}public synchronized void update(String p_data) {syncUpdateIn();//Update properties
 }private synchronized void syncUpdateIn() {while (readCount > 0) {try {wait();} catch (Exception e) {}}}private synchronized void syncReadIn() {readCount++;}private synchronized void syncReadOut() {readCount--;notifyAll();}public Vector getProperties() {syncReadIn();//Process data
  syncReadOut();return properties;}}

public class GlobalConfig {private static GlobalConfig instance = null;private Vector properties = null;private GlobalConfig() {//Load configuration information from DB or file//Set values for properties
    }private static synchronized void syncInit() {if (instance = null) {instance = new GlobalConfig();}}public static GlobalConfig getInstance() {if (instance = null) {syncInit();}return instance;}public Vector getProperties() {return properties;}public void updateProperties() {//Load updated configuration information by new a GlobalConfig objectGlobalConfig shadow = new GlobalConfig();properties = shadow.getProperties();}}