In this chapter, you learned that simple types are value-type structs but can still be used anywhere objects are expected in a program due to boxing and unboxing conversions. You learned that linked lists are collections of data items that are “linked together in a chain.” You also learned that a program can perform insertions and deletions anywhere in a linked list (though our implementation performed insertions and deletions only at the ends of the list). We demonstrated that the stack and queue data structures are constrained versions of lists. For stacks, you saw that insertions and deletions are made only at the top—so stacks are known as last-in, first out (LIFO) data structures. For queues, which represent waiting lines, you saw that insertions are made at the tail and deletions are made from the head—so queues are known as first-in, first out (FIFO) data structures. We also presented the binary tree data structure. You saw a binary search tree that facilitated high-speed searching and sorting of data and efficient duplicate elimination. In the next chapter, we introduce generics, which allow you to declare a family of classes and methods that implement the same functionality on any type.