Boilerplate code

Code that has to be included in many places with little or no alteration

In computer programming, boilerplate code, or simply boilerplate, are sections of code that are repeated in multiple places with little to no variation. When using languages that are considered verbose, the programmer must write a lot of boilerplate code to accomplish only minor functionality. The need for boilerplate can be reduced through high level mechanisms such as metaprogramming (which has the computer automatically write the needed boilerplate code or insert it at compile time), convention over configuration (which provides good default values, reducing the need to specify program details in every project) and model driven engineering (which uses models and model to code generators, eliminating the need for manual boilerplate code). It is also possible to move boilerplate code to an abstract class so that it can be inherited by any number of concrete classes. Another option would be to move it into a subroutine so that it can be called instead of being duplicated.

The term arose from the newspaper business. Columns and other pieces that were distributed by print syndicates were sent to subscribing newspapers in the form of prepared printing plates. Because of their resemblance to the metal plates used in the making of boilers, they became known as "boiler plates", and their resulting text—"boilerplate text". As the stories that were distributed by boiler plates were usually "fillers" rather than "serious" news, the term became synonymous with unoriginal, repeated text. A related term is bookkeeping code, referring to code that is not part of the business logic but is interleaved with it in order to keep data structures updated or handle secondary aspects of the program.

In Java programs, DTO classes are often provided with methods for getting and setting instance variables. The definitions of these methods can frequently be regarded as boilerplate. Although the code will vary from one class to another, it is sufficiently stereotypical in structure that it would be better generated automatically than written by hand. For example, in the following Java class representing a pet, almost all the code is boilerplate except for the declarations of Pet, name, and owner:

In addition to declarations, methods in OOP languages also contribute to the amount of boilerplate. A 2015 study on popular Java projects shows that 60% of methods can be uniquely identified by the occurrence of 4.6% of its tokens, making the remaining 95.4% boilerplate irrelevant to logic. The researchers believe this result would translate to subroutines in procedural languages in general.