Java Programming

Write a program to sign people up for a seminar. Everybody is assigned an ID number in [0, 30]. It will start with a simple routine that asks users to type in their number. Once you have the array of up to 30 numbers (each one in [0, 30], you will want to check whether some people may have entered their numbers twice or not. Write a program, which can show the following information:

a. ALL numbers in the array that have duplicates

b. The two most frequently appeared numbers