This chapter includes 30 problems that involve arrays, collections, and several data structures. The aim is to provide solutions to a category of problems encountered in a wide range of applications, including sorting, finding, comparing, ordering, reversing, filling, merging, copying, and replacing. The solutions provided are implemented in Java 8-12 and they can also be used as a basis for solving other related issues. At the end of this chapter, you will have at your disposal a solid breadth of knowledge that will prove useful in solving a variety of problems involving arrays, collections, and data structures.