Page Comparison

This page documents the standard adopted for Java code in the Continuuity Cask project(s).

All committers are expected to follow these standards; checkstyle Checkstyle or similar (lyntLynt) is used to check compliance.

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Indent using two spaces. No tabs.

braces Braces always go on same line, e.g.

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Java source files must have a ".java" suffix (this will be enforced by the compiler) [mandatory].
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].
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].
Source files should not exceed 1500 lines [recommended].
No line in a source file should exceed 120 characters [mandatory].
The sections of a source file should be presented in the following order [mandatory]:
1. Copyright Information
2. File information comment (see rule 7 below).
3. Package name (see rules 1 to 3 in the section 2.1 above and rule 8 below).
4. Imports (see rules 9 to 10 below).
5. Other class definitions.
6. Public class definition.
Every class that is to be released must be a member of a package [mandatory].
1. 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.
All class imports from the same package should be grouped together. A single blank line should separate imports from different packages [recommended]. The actual order of imports must be as follows, with each group ordered lexically:
1. all comco.continuuitycask
2. all other but non-java
3. all java[x]
No import package.* allowed. Classes must be imported one by one [mandatory].
Use javadoc Javadoc tags and use HTML mark-up to enhance the readability of the output files [mandatory].
Every package can should provide package-info.html [recommended].

Compilation

This section defines the general rules associated with results of compiling a Java source file.

Compiling a java Java source should not result in undefined documentation compilation errors [mandatory].
Compiling a java Java source should result in no warnings [mandatory].

Java Elements

This section gives advice on coding the various elements of the Java programming language.

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Class names should start with a capital letter with every subsequent word capitalised, for example: DataProcessor [mandatory].
The name of exception classes should end in the word exception, for example: UnknownMungeException [mandatory].
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.
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 2 spaces more than their enclosing class [mandatory].
Declare a class as final only if specialisation specialization 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].
For all but simplest classes the following methods should have useful definitions [recommended]:
```
public boolean equals(Object obj)
public int hashCode()
public String toString()
```
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.
The order of presentation of variables in a class definition should be [recommended]:
1. private, protected, public: static final variables (aka constant class variables).
2. private, protected, public: static variables (aka class variables).
3. private, protected, public: final variables (aka constant instance variables).
4. private, protected, public: variables (aka instance variables).
  It should be noted that as javadoc Javadoc will automatically order variables in a consistent manner, rigid adherence to this rule is not necessary.
Variable modifiers must be presented in the following order: static, final, transient, volatile [mandatory].
The names of static final variables should be upper case with subsequent words prefixed with an underscore [mandatory]. For example:
```
public static final int NOT_FOUND = -1;
```
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.
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:
```
String name;
String[] childrensNames;
```
Class and instance variables must be prefixed with an underscore (_) [mandatory].
Variables must not be named using the so-called Hungarian notation [mandatory]. For example:
```
int nCount = 4; // not allowed
```
Only one variable may be defined per line [mandatory].
Variable declarations should be indented 4 2 spaces more than their enclosing class [mandatory].
All variables should be preceded by a comment that explains what the variable is for, where it is used and so forth, unless it is obvious. The comment should not be a JavaDocJavadoc, unless it is a public or protected variable.
All public constants must be preceded by a JavaDoc Javadoc that explains the meaning of the constant [mandatory].
Never declare instance variables as public unless the class is effectively a "struct" [mandatory].
Never give a variable the same name as a variable in a superclass [mandatory].

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Constructors and finalize methods should follow immediately after the variable declarations [mandatory].
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 Javadoc [mandatory]. Note that private implies final.
Methods that are associated with the same area of functionality should be physically close to one another [recommended].
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 Javadoc will automatically order methods in a consistent manner, rigid adherence to this rule is not necessary.
Method modifiers should be presented in the following order: abstract, static, final., synchronized [mandatory]
When a synchronized method is overloaded, it should be explicitly synchronized in the subclass [recommended].
Method names should start with a lower case letter with all subsequent words being capitalised [mandatory]. For example:
```
protected int resize(int newSize)
protected void addContentsTo(Container destinationContainer)
```
Methods which get and set values should be named as follows [mandatory]:
```
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".
Method definitions should be indented 4 2 spaces more than their enclosing class [mandatory].
All methods should be preceded by a javadoc Javadoc comment specifying what the method is for, detailing all arguments, returns and possible exceptions. This comment should be of the following form and be indented to the same level as the method it refers to [mandatory]:
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:
```
public void munge() {
    int i;
    // method definition omitted...
}
```
The body of a method should be indented 4 2 columns further that the opening and closing braces associated with it [mandatory]. See the above rule for an example.
When declaring and calling methods there should be no white space whitespace before or after the parenthesis [mandatory].
In argument lists there should be no white space before a comma, and only a single space (or newline) after it [mandatory]. For example:
```
public void munge(int depth, String name) {
    if (depth > 0) {
        munge(depth - 1, name);
    }
    // do something
}
```
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.
The method public static void main() should not be used for test purposes. Instead a test/demo program should be supplied separately. [mandatory].
Public access methods (i.e. methods that get and set attributes) should only be supplied when required [mandatory].
If an instance method has no natural return value, declare it as void rather than using the "return this;" convention [mandatory].

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Unary operators should not be separated from their operand by white space [mandatory].
Embedded ++ or – operators should only be used when it improves code clarity [recommended]. This is rare.
Extra parenthesis should be used in expressions to improve their clarity [recommended].
The logical expression operand of the "?:" (ternary) operator must be enclosed in parenthesis. If the other operands are also expressions then they should also be enclosed in parenthesis [mandatory]. For example:
```
biggest = (a > b) ? a : b;
complex = (a + b > 100) ? (100 * c) : (10 * d);
```
Nested "?:" (ternary) operators can be confusing and should be avoided [mandatory].
Use of the binary "," operator (the comma operator) should be avoided [mandatory]. Putting all the work of a for loop on a single line is not a sign of great wisdom and talent.
If an expression is too long for a line (i.e. extends beyond column 119120) then it should be split after the lowest precedence operator near the break [mandatory]. For example:
```
if ((state == NEED_TO_REPLY) ||
    (state == REPLY_ACK_TIMEOUT)) {
    // (re)send the reply and enter state WAITING_FOR_REPLY_ACK
}
```
Furthermore if an expression requires to be split more than once, then the split should occur at the same logical level, if possible.

All binary and ternary operators (,with the exception for of ".") , should be separated from their operands by a space [mandatory].

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The body of a compound statement should be indented by 4 2 spaces more than the enclosing braces [mandatory]. See the following rule for an example.
The braces associated with a compound statement should be on their own line and be indented to the same level as the surrounding code [mandatory]. For example:
```
if ((length >= LEN_BOX) && (width >= WID_BOX)) {
    int i;
    // Statements omitted...
}
```
If the opening and closing braces associated with a compound statement are further than 20 lines apart then the closing brace should annotated as follows [mandatory]:
```
for (int j = 0; j < SIZE; j++) {
    lotsOfCode();
} // end for
```
All statements associated with an if or if-else statement should be made compound by the use of braces [mandatory]. For example:
```
if (a > b){
    statement();
} else {
    statement1();
    statement2();
}
```
The case labels in a switch statement should be on their own line and indented by a further 4 2 spaces. The statements associated with the label should be indented by 4 2 columns more than the label and not be enclosed in a compound statement. [mandatory]. For example:
```
switch (tState) {
    case NOT_RUNNING:
        start();
        break;

    case RUNNING: // FALLTHROUGH
    default:
        monitor();
        break;
}
```
In switch statements - the statements associated with all cases should terminate with a statement which explicitly determines the flow of control, for example break [recommended].
In switch statements - fall through should be avoided wherever possible, however if it is unavoidable it must be commented with "// FALLTHROUGH" [mandatory].

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Versions Compared

Old Version 1

New Version 2

Key

Compilation

Java Elements