一个单例工厂类，要求线程安全？

1.双重检查加锁

public class test {
private volatile static test uniqueInstance = null;

private test(){

}

public static test getInstance(){
if(uniqueInstance == null){
synchronized (test.class){
if(uniqueInstance == null){
uniqueInstance = new test();
}
}
}
return uniqueInstance;
}
}