what does the abstract keyword dowhat are

Question

1. What does the abstract keyword do?
2. What are generics as they relate to the built in linked list class? Why do we need them?
3. What is the purpose of try/catch and exception handling?
4. Given an employee object which contains a field for first name, last name, and phone number. Write the necessary JSON to represent a list of two employees. You may make up their first name, last name, and phone numbers.
5. Write a method named factorial that takes an int as a parameter and returns the factorial of that number. You must write this method recursively.
6. In Java, write the employee class from question number four. You should provide an appropriate constructor as well as getter methods.
7. Write a method named doubleLetters which takes a string as a parameter and returns a new string with each character in the original doubled. For example: "cat" becomes "ccaatt"
8. Write a class called Stack which stores char primitive types in a stack data structure. Make sure to provide the necessary methods: push, pop, and peak.
9. Convert "MIKE" from base 16 to base 10.
10. Convert "111011010" from binary to octal.

Small Questions for the expert after the assignment is completed:

1) Which parts of the assignment were you not able to complete fully? For each, explain why you were unable to complete this part and what steps you took to attempt to complete it. Give me as much detail as possible such that I may award partial credit where it is due.

2)what would you do differently if you could do this assignment again?