Oracle Java Developer interview questions

String,String buffer,String builder difference. Can u write your own immutable class n how? hashmap implementation and hashcode(),equals() method he asked me to write 2 logical testing programs with reduced complexity( 0,1,1,2,4,5,3,3,1,0,1 traverse once only n get the duplicate number's along with the count). printing pascal triangle duplicate letter from a string with less complexity reversing words of string individually(this is a tree---o/p: siht si a eert)

Some advanced database questions for a java developer position.