Java开发工程师常见笔试题及答案

单例模式

饿汉式
classSingleton{
privatestaticSingletoninstance=newSingleton();
privateSingleton(){}
staticSingletongetInstance(){
returninstance;
}
}
懒汉式
classSingleton{
privatestaticSingletoninstance=null;
privateSingleton(){}
staticSingletongetInstance(){
if(instance==null)
instance=newSingleton();
returninstance;
}
}

sql语句

查找表中多余的重复记录，重复记录是根据单个字段（peopleId）来判断
select*frompeople
wherepeopleIdin(selectpeopleIdfrompeoplegroupbypeopleIdhavingcount(peopleId)>1)