给定以下多重元素:publicclassMultiton{privatestaticfinalMultiton[]instances=newMultiton[...];privateMultiton(...){//...}publicstaticMultitongetInstance(intwhich){if(instances[which]==null){instances[which]=newMultiton(...);}returninstances[which];}}在没有getInstance()方法昂贵的同步和双重检查锁定的争议的情况下，我们如何才能保持线程安全和惰性？提到