Package names

• Package names should be all lower case without underscores or other special characters.
• Package names begin with the reversed authority part of the web address of the company of the developer. This part can be followed a by project/program structure dependent package substructure.
• Don’t use plural form. Follow the convention of the standard API which uses for instance java.lang.annotation and not java.lang.annotations.
• Examples: com.yourcompany.widget.button, com.yourcompany.core.api

Class, Interface and Enum Names

• Class and enum names should typically be nouns.
• Interface names should typically be nouns or adjectives ending with …able.
• Use mixed case with the first letter in each word in upper case (i.e. CamelCase).
• Match the regular expression ^[A-Z][a-zA-Z0-9]*$.
• Use whole words and avoid using abbreviations unless the abbreviation is more widely used than the long form.
• Format an abbreviation as a word if the it is part of a longer class name.
• Examples: ArrayList, BigInteger, ArrayIndexOutOfBoundsException, Iterable.

Method Names

Method names should typically be verbs or other descriptions of actions

• They should match the regular expression ^[a-z][a-zA-Z0-9]*$.
• Use mixed case with the first letter in lower case.
• Examples: toString, hashCode

Variables

Variable names should be in mixed case with the first letter in lower case

• Match the regular expression ^[a-z][a-zA-Z0-9]*$
• Further recommendation: Variables
• Examples: elements, currentIndex

Type Variables

For simple cases where there are few type variables involved use a single upper case letter.

• Match the regular expression ^[A-Z][0-9]?$
• If one letter is more descriptive than another (such as K and V for keys and values in maps or R for a function return type) use that, otherwise use T.
• For complex cases where single letter type variables become confusing, use longer names written in all capital letters and use underscore (\_) to separate words.
• Examples: T, V, SRC_VERTEX

Constants

Constants (static final fields whose content is immutable, by language rules or by convention) should be named with all capital letters and underscore (\_) to separate words.

• Match the regular expression ^[A-Z][A-Z0-9]*(_[A-Z0-9]+)*$
• Examples: BUFFER_SIZE, MAX_LEVEL

Other guidelines on naming

• Avoid hiding/shadowing methods, variables and type variables in outer scopes.
• Let the verbosity of the name correlate to the size of the scope. (For instance, use descriptive names for fields of large classes and brief names for local short-lived variables.)
• When naming public static members, let the identifier be self descriptive if you believe they will be statically imported.
• Further reading: Naming Section (in the official Java Style Guide)

Source: Java Style Guidelines from Oracle