My Java Code Style

My Java code style: a collection of Java good practices.

Today I want to talk about my own Java code style. It’s been 2 years that I coded professionally, since my intern at Google Summer of Code. Most of the time, I write Java. So I want to do a summery on this field. This blog post will keep update on the next months.


  • Marks utility class as final. All methods in a utility class are static, extending such class does not make sense: static methods cannot be overridden.
  • Use private constructor for utility class.
  • Data class should be immutable. The less mutable state, the easier it is to ensure thread safe. (Immutable objects are automatically thread-safe)


  • Mark class variable as final. It ensures the variable is initialized and is initialized only once, either in constructor or at declaration. Its reference is never changed during object’s lifecycle.
  • Never use null for variable assignment.
  • Never use final for method parameter.
  • Never use final for local variable. This increases the readability.


  • Don’t restrict method input to List<T> if possible, use Iterable<T>.
  • Provide 2 choices for iterable method input: Iterable<T> and T....
  • Always use @Override.
  • Name method as getXXX when it’s a getter method.
  • Name method as hasXXX or isXXX if a boolean is returned.


  • Use camel-case for enum class name.
  • Use upper-case for enum members.
  • Marks a enum variable as public if it is immutable and needs to be referenced from outside. This avoids unnecessary getter method.
  • Avoid using switch to implement logic. It can cause errors when new member(s) added into the enum. Attach the logic directly into the enum.


  • Never use null for variable assignment.
  • Use no-op pattern if there’s nothing to do.
  • Use Optional<T> as result type, if the result is nullable.


  • Don’t throw exception if possible. Consider failures as a possible result—use something like Try<T> instead of only returning the correct result.
  • Use only one exception type for one module. It helps to handle unexpected cases.


  • Use one-line lambda
  • Use method reference for lambda whenever possible


  1. Scala - scala.util.Try[+T]
  2. EGit/Contributor Guide - Coding Standards
  3. Google Gerrit Code Review - Contributing, Style
  4. Devoxx FR 2018: Clean Code with Java8 4 years later (V. Rentea)
  5. Java Concurrency in Priactice, chapter 5 summary (page 110)