public class Singleton {

private static Singleton instance=null;

private Singleton(){

}

private static synchronized void syncInitSigleton(){

if(instance==null){

instance=new Singleton();

}

}

public static Singleton getInstance(){

if(instance==null){

syncInitSigleton();

}

return instance;

}

public Object readResolve(){

return instance;

}

public void doSomething(){

System.out.println("This is a singleton.");

}

}

/*

//内部类实现的单例模式

public class Singleton {

// 私有构造方法，防止被实例化

private Singleton() {

}

// 此处使用一个内部类来维护单例

private static class SingletonFactory {

private static Singleton instance = new Singleton();

}

// 获取实例

public static Singleton getInstance() {

return SingletonFactory.instance;

}

// 如果该对象被用于序列化，可以保证对象在序列化前后保持一致

public Object readResolve() {

return getInstance();

}

public void doSomething(){

System.out.println("This is a singleton.");

}

}

//影子实例实现对单例对象属性的同步更新

public class Singleton {

private static Singleton instance = null;

private Vector properties = null;

public Vector getProperties() {

return properties;

}

private Singleton() {

}

private static synchronized void syncInit() {

if (instance == null) {

instance = new Singleton();

}

}

public static Singleton getInstance() {

if (instance == null) {

syncInit();

}

return instance;

}

public void doSomething(){

System.out.println("This is a singleton.");

}

public void updateProperties() {

Singleton shadow = new Singleton();

properties = shadow.getProperties();

}

} */