Can you please help me in this homework?

EX 3.2 List the collections in the Java Collections API and mark the ones that are covered in this text.

EX 3.6 What should be the time complexity of the isEmpty(), size(), and toString() methods?

EX 3.9 Draw an example using the five integers (12, 23, 1, 45, 9) of how a stack could be used to reverse the order (9, 45, 1, 23, 12) of these elements.

PP 3.2 Design and implement an application that reads a sentence from the user and prints the sentence with the characters of each word backwards. Use a stack to reverse the characters of each word.