Kotlin Code style guidelines
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The document outlines coding style guidelines by Sanjay Hans for Kotlin programming, emphasizing naming conventions, spacing, and structure within code. It includes specifics on class and variable naming, indentation practices, the use of semicolons, and annotations. Additionally, it offers XML guidance relevant to Android development and provides resources for further reference.
Kotlin Code style guidelines
- 1. Code Style Guidelines By Sanjay Hans
- 2. Nomenclature Declarations Spacing Semicolons Brace Style When Statements Annotations Types Xml Guidance Language Credit TOC
- 3. Nomenclature Packages Package names are similar to Java: all lower-case, multiple words concatenated together, without hyphens or underscores: org.example.kotlin Classes & Interfaces Names of classes and objects start with an upper case letter and use the camel case: class DeclarationProcessor Function names Names of functions, properties and local variables start with a lower case letter and use the camel case and no underscores: fun processDeclaration(){/*…*/} var declarionCount = 1
- 4. Property names Constant values in the companion object should be written in uppercase, with an underscore separating words: class const val MAX_COUNT = 8 val USER_NAME_FIELD = "UserName" Variables & Parameters Written in lowerCamelCase. Single character values must be avoided, except for temporary looping variables.
- 5. Declarations Visibility Modifiers Only include visibility modifiers if you need something other than the default of public. Fields & Variables Prefer single declaration per line. username: String twitterHandle: String Classes Exactly one class per source file, although inner classes are encouraged where scoping appropriate.
- 6. Data Type Objects Prefer data classes for simple data holding objects. Enum Classes Enum classes without methods may be formatted without line-breaks, as follows: private enum CompassDirection { EAST, NORTH, WEST, SOUTH }
- 7. Spacing Indentation Indentation is using spaces - never tabs. Blocks Indentation for blocks uses 2 spaces (not the default 4): Line Wraps Indentation for line wraps should use 4 spaces (not the default 8):
- 8. Line Length Lines should be no longer than 100 characters long. Vertical Spacing There should be exactly one blank line between methods to aid in visual clarity and organization. Whitespace within methods should separate functionality, but having too many sections in a method often means you should refactor into several methods. Semicolons: Semicolons are dead to us should be avoided wherever possible in Kotlin.
- 9. Brace Style Unlike Java, direct access to fields in Kotlin is preferred.
- 10. When Statements Unlike switch statements in Java, when statements do not fall through. Separate cases using commas if they should be handled the same way. Always include the else case.
- 11. Annotations Standard annotations should be used - in particular override. This should appear on the same line as the function declaration.
- 12. Types Always use Kotlin's native types when available. Type Inference Type inference should be preferred where possible to explicitly declared types. val something = MyType() val meaningOfLife = 42 Constants vs. Variables Constants are defined using the val keyword, and variables with the var keyword. Always use val instead of var if the value of the variable will not change.
- 13. XML Guidance Since Android uses XML extensively in addition to Java, we have some rules specific to XML. XML File Names View-based XML files should be prefixed with the type of view that they represent. • activity_login.xml • fragment_main_screen.xml • button_rounded_edges.xml Use Context-Specific XML Files •Strings => res/values/strings.xml •Styles => res/values/styles.xml •Colors => res/color/colors.xml •Animations => res/anim/ •Drawable => res/drawable Language Use US English spelling. String color = "red";
- 14. Useful resources https://kotlinlang.org/docs/reference/coding- conventions.html https://developer.android.com/kotlin/style-guide https://source.android.com/setup/contribute/code-style https://github.com/raywenderlich/kotlin-style-guide https://jakewharton.com/just-say-no-to-hungarian-notation/
- 15. Q&A
Editor's Notes
- #7: 1