public class SingletonDemo5 implements Serializable{

private static SingletonDemo5 instance;

//防止单例被反射

private SingletonDemo5(){

if(null!=instance){

throw new RuntimeException("不能被反射");

}

}

/* public static synchronized SingletonDemo2 getInstance(){

if(null==instance){

return instance=new SingletonDemo2();

}

return instance;

}*/

//资源不够优化，可以进行双重检查，注释部分

public static SingletonDemo5 getInstance(){

//双重检查，提高效率

if(null==instance){

synchronized (SingletonDemo5.class) {

if(null==instance){

instance=new SingletonDemo5();

}

}

}

return instance;

}

//当反序列化的时候，直接调用当前的对象

private Object readResolve(){

return instance;

}

}

 

public class Test2 {

public static void main(String[] args) throws IOException, ClassNotFoundException {

SingletonDemo5 s1=SingletonDemo5.getInstance();

SingletonDemo5 s2=SingletonDemo5.getInstance();

System.out.println(s1);

System.out.println(s2);

//注释  readResolve()方法的时候

//s1 com.my.design.single.SingletonDemo5@15db9742

//s2 com.my.design.single.SingletonDemo5@15db9742

//s3 com.my.design.single.SingletonDemo5@e9e54c2

File file=new File("d:/a.txt");

FileOutputStream fos=new FileOutputStream(file);

ObjectOutputStream os=new ObjectOutputStream(fos);

os.writeObject(s1);

ObjectInputStream is=new ObjectInputStream(new FileInputStream(file));

SingletonDemo5 s3=(SingletonDemo5) is.readObject();

System.out.println(s3);

}

}

//没注释 readResolve()方法的时候

//s1 com.my.design.single.SingletonDemo5@15db9742

//s2 com.my.design.single.SingletonDemo5@15db9742

//s3 com.my.design.single.SingletonDemo5@15db9742

前面是防止反序列化，如果要防止反射的话可以在构造器中抛出异常