Lesson 12 is the first of four lessons on lambda expressions. Lambdas are Java's way of representing functions. The lesson introduces lambda expressions and illustrates how their use can make your code more flexible and reusable. The lesson closes with two examples of applications that would be difficult and cumbersome without lambdas but which are relatively simple and short with them. The first is a numerical integration routine, and the second is a reusable tool for collecting performance-timing results.