vavrtom commented on a change in pull request #36: QPID-8361: [Broker-J] Create a developer guide for Qpid Broker-J URL: https://github.com/apache/qpid-broker-j/pull/36#discussion_r324152658
########## File path: doc/developer-guide/src/main/markdown/code-guide.md ########## @@ -0,0 +1,446 @@ +# Qpid Broker-J Coding Standards + +This article documents the standard adopted for Java code in the Qpid project. +All committers are expected to follow this standard. + +## Executive Summary + +The main things for layout purposes in the standard are: + + * Indent using four spaces. No tabs. + * braces always go on new lines, e.g. +```java +if (x == 5) +{ + System.out.println("Hello"); +} +``` + +rather than + +```java +if (x == 5} { + System.out.println("Hello"); +} +``` + +Always add braces, e.g. + +```java + if (x == 5) + { + System.out.println("Hello"); + } +``` +rather than + +```java +if (x == 5} + System.out.println("Hello"); +``` + +Fields prefixed with underscores, e.g. `_messageCount` + +Spaces after keywords but no spaces either before or after parentheses in method calls, e.g. + +```java + if (x == 5) +``` + +rather than + +```java + if(x==5) +``` + +but + +```java + foo.bar(4, 5) +``` + +rather than + +```java + foo.bar( 4, 5 ) +``` + +## Details + +### Introduction + +This document describes two types of coding standard: + +1. **Mandatory** standards must be followed at all times. +2. **Recommended** standards should in general be followed but in particular cases may be omitted + where the programmer feels that there is a good reason to do so. + +Code that does not adhere to mandatory standards will not pass the automated checks +(or a code review if the guideline is not stylistic). + +### Source files + +This section defines the general rules associated with the contents of a Java source file and the order +in which the each part should be presented. No rules on programming style, naming conventions or indentation are given here. + +1. Java source files must have a ".java" suffix (this will be enforced by the compiler) [mandatory]. +2. The basename of a Java source file must be the same as the public class defined therein + (this will be enforced by the compiler) [mandatory]. +3. Only one class should be defined per source file (except for inner classes and one-shot uses + where the non-public class cannot conceivably be used outside of its context) [mandatory]. +4. Source files should not exceed 1500 lines [recommended]. +5. No line in a source file should exceed 120 characters [mandatory]. +6. The sections of a source file should be presented in the following order [mandatory]: + * File information comment (see rule 7 below). + * Package name (see rules 1 to 3 in the section 2.1 above and rule 8 below). + * Imports (see rules 9 to 10 below). + * Other class definitions. + * Public class definition. +7. Do not use automatically expanded log or revision number provided by your source code management system + unless it provides a facility to avoid "false conflicts" when doing merges due simply to revision number changes + (which happens, for example, with cvs when branches are used). [mandatory] +8. Every class that is to be released must be a member of a package [mandatory]. + Rationale: classes that are not explicitly put in a package are placed in the unnamed package by the compiler. + Therefore as the classes from many developers will be being placed in the same package the likelihood of a name + clash is greatly increased. +9. All class imports from the same package should be grouped together. A single blank line should separate imports + from different packages [recommended]. +10. Use javadoc tags and use HTML mark-up to enhance the readability of the output files [mandatory]. + +### Java Elements + +This section gives advice on coding the various elements of the Java programming language. + +#### Class definitions + +This section gives guidelines for class and interface definitions in Java. +The term class in this section is used more broadly to mean class and interface: + +1. Class names should start with a capital letter with every subsequent word capitalised, + for example: `DataProcessor` [mandatory]. +2. All classes should be preceded by a javadoc comment describing the purpose of the class [recommended]. +3. Class-level javadoc comments should specify the thread-safety of the class [recommended]. +4. The name of exception classes should end in the word exception, for example: UnknownMungeException [mandatory]. +5. Class names should in general not be overloaded. For example, defining a class "com.foo.bar.String" + should be avoided as there is already a class "java.lang.String" [recommended]. + Rationale: adhering to this rule reduces the likelihood of confusion and means that the use of fully qualified + class names should not be required. +6. The definition of the primary class (i.e. the class with the same name as the java file) should start in column 0 + of the source file. Inner class definitions should be indented 4 spaces more than their enclosing class [mandatory]. +7. Declare a class as final only if specialisation will never be required and improved performance is essential. + With modern JVMs there in fact may be no performance advantage. Warning: use of final limits code reuse [mandatory]. +8. For all but simplest classes the following methods should have useful definitions [recommended]: + ```java + public boolean equals(Object obj) + public int hashCode() + public String toString() + ``` +9. The order of presentation of the sections in a class should be [mandatory]: + * Variables + * Methods + +#### Variables +This section gives guidelines for class and instance variable definitions in Java. +In this section if a rule uses the term variable rather than instance variable or class variable, +then the rule applies to both types of variable. + +1. The order of presentation of variables in a class definition should be [recommended]: + * private, protected, public: static final variables (aka constant class variables). + * private, protected, public: static variables (aka class variables). + * private, protected, public: final variables (aka constant instance variables). + * private, protected, public: variables (aka instance variables). + It should be noted that as javadoc will automatically order variables in a consistent manner, + rigid adherence to this rule is not necessary. +2. Variable modifiers should be presented in the following order: static, final, transient, volatile [mandatory]. +3. The names of static final variables should be upper case with subsequent words prefixed with an underscore [mandatory]. + For example: + ```java + public static final int NOT_FOUND = -1; + ``` +4. When a subclass refers to a static final variable defined in a parent class, access should be qualified + by specifying the defining class name [mandatory]. + For example: use `ParentClass.MAX` rather than `MAX`. +5. The names of variables (other that static final) should start with a lower case letter. + Any words that are contained in the rest of the variable name should be capitalised [mandatory]. + For example: + ```java + String name; + String[] childrensNames; + ``` +6. Class and instance variables must be prefixed with an underscore (_) [mandatory]. +7. Variables must not be named using the so-called Hungarian notation [mandatory]. + For example: + ```java + int nCount = 4; // not allowed + ``` +8. Only one variable may be defined per line [mandatory]. +9. Variable declarations should be indented 4 spaces more than their enclosing class [mandatory]. +10. All variables should be preceded by a javadoc comment that specifies what the variable is for, + where it is used and so forth. The comment should be of the following form and be indented + to the same level as the variable it refers to [recommended] +11. Never declare instance variables as public unless the class is effectively a "struct" [mandatory]. +12. Never give a variable the same name as a variable in a superclass [mandatory]. +13. Ensure that all non-private class variables have sensible values even if no instances have been created + (use static initialisers if necessary, i.e.`static { ... }`) [mandatory]. + Rationale: prevents other objects accessing fields with undefined/unexpected values. + +#### Methods +This section gives guidelines for class and instance method definitions in Java. +In this section if a rule uses the term method rather than instance method or class method, +then the rule applies to both types of method. + +1. Constructors and finalize methods should follow immediately after the variable declarations [mandatory]. +2. Do not call non-final methods from constructors. This can lead to unexpected results when the class is subclassed. + If you must call non-final methods from constructors, document this in the constructor's javadoc [mandatory]. + Note that private implies final. +3. Methods that are associated with the same area of functionality should be physically close to one another [recommended]. +4. After grouping by functionality, methods should be presented in the following order [recommended]: + * private, protected, public: static methods. + * private, protected, public: instance methods. + It should be noted that as javadoc will automatically order methods in a consistent manner, + rigid adherence to this rule is not necessary. +5. Method modifiers should be presented in the following order: abstract, static, final., synchronized [mandatory] +6. When a synchronized method is overloaded, it should be explicitly synchronized in the subclass [recommended]. +7. Method names should start with a lower case letter with all subsequent words being capitalised [mandatory]. + For example: + ```java + protected int resize(int newSize) + protected void addContentsTo(Container destinationContainer) + ``` +8. Methods which get and set values should be named as follows [mandatory]: + ```java + Type getVariableName() + void setVariableName(Type newValue) + ``` + Exceptions should be used to report any failure to get or set a value. + The "@param" description should detail any assumptions made by the implementation, + for example: "Specifying a null value will cause an error to be reported". +9. Method definitions should be indented 4 spaces more than their enclosing class [mandatory]. +10. All non-private methods should be preceded by a javadoc comment specifying what the method is for, + detailing all arguments, returns and possible exceptions [mandatory] +11. The braces associated with a method should be on a line on their own and be indented to the same level + as the method [mandatory]. For example: + ```java + public void munge() + { + int i; + // method definition omitted... + } + ``` +12. The body of a method should be indented 4 columns further that the opening and closing braces associated with it [mandatory]. + See the above rule for an example. +13. When declaring and calling methods there should be no white space before or after the parenthesis [mandatory]. +14. In argument lists there should be no white space before a comma, and only a single space (or newline) after it [mandatory]. + For example: + ```java + public void munge(int depth, String name) + { + if (depth > 0) + { + munge(depth - 1, name); + } + // do something + } + ``` +15. Wherever reasonable define a default constructor (i.e. one that takes no arguments) + so that `Class.newInstance()` may be used [recommended]. If an instance which was created by default construction + could be used until further initialisation has been performed, then all unserviceable requests should cause + a runtime exception to be thrown. +16. The method public static void main() should not be used for test purposes. + Instead a test/demo program should be supplied separately. [mandatory]. +17. Public access methods (i.e. methods that get and set attributes) should only be supplied when required [mandatory]. +18. If an instance method has no natural return value, declare it as void rather than using the "return this;" + convention [mandatory]. +19. Ensure that non-private static methods behave sensibly if no instances of the defining class have been created [mandatory]. + +### Expressions +This section defines the rules to be used for Java expressions: + +1. Unary operators should not be separated from their operand by white space [mandatory]. +2. Embedded ++ or – operators should only be used when it improves code clarity [recommended]. This is rare. 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