The document contains code for multiple classes and methods: 1. A tanSo method that takes a 2D integer array as input and returns a HashMap counting the occurrences of each unique number. 2. A kiemTraBoiSo2 method that takes an Iterator of Integers and returns true if any element is even. 3. ThiSinh, DotThi and MasterCheft classes that model exam students, exam sessions, and a competition respectively - ThiSinh stores scores per session and calculates a total, MasterCheft manages a sorted set of students. 4. A CaesarCoding class that implements Caesar cipher encryption/decryption on alphabetic characters using mapping tables