A Philosophy of Software Design

by John Ousterhout

Splitting and joining methods The issue of when to subdivide applies not just to classes, but also to methods: are there times when it is better to divide an existing method into multiple smaller methods? Or, should two smaller methods be combined into one larger one? Long methods tend to be more difficult to understand than shorter ones, so many people argue that length alone is a good justification for breaking up a method. Students in classes are often given rigid criteria, such as “Split up any method longer than 20 lines!” However, length by itself is rarely a good reason for splitting up a method. In general, developers tend to break up methods too much. Splitting up a method introduces additional interfaces, which add to complexity. It also separates the pieces of the original method, which makes the code harder to read if the pieces are actually related. You shouldn’t break up a method unless it makes the overall system simpler; I’ll discuss how this might happen below.