HCLTech Technical Lead interview questions

1)Explain OOPS 2)Difference between String Buffer and String Builder 3)Why String is immutable 4)Write a programme to retrieve second large number in the list with out using API's 5)Write a programme to remove duplicate characters from String 6)Asked to write a programme for pattern 7)Difference between runnable and callable 8)How do you inject abstract method using spring 9)Difference between synchronized block and explict syncronized keyword on a method 10)what is fail fast and fail sage, give examples 11)Difference between get and load in hibernate 12)Write a rest api for upload and download a file 13)difference between put and post