Morgan Stanley Software Engineer interview questions

How does JVM manage cyclic references? Does JVM collect variables that have cyclic references? What are different types of locks in multi-threading? Do you know about semaphore lock? What is a good hashcode? How to generate hashcode? How does map.put work? what is the complexity of hashtable? If you have a very large text file. You have comma separated characters. How do you know how many times a word appeared? How will you print the first maximum top 10 words.