PTC Software Specialist interview questions

There were one technical round and one managerial round. Each round had two interviewers. Technical round: They started with core java and then jumped into hibernate and JPA, then in spring boot.

2 interview Rounds - 1st round - 1) write a own string class and implement string functions such as strlen etc , 2) difference between Linked list and Vector wihch has insertion effieceint 3) do you know the design patterns, explain singletone design pattern 4) copy constructor