Headers

Look at the Headers document for more information.

Indentations

4 spaces. NO tabs.

Javadoc

All API interfaces and classes must be fully documented through javadocs comments at interface/class, method and package level.

When you inherit or extend from another interface or class which is already documented, and implement or rewrite one of the parent methods, don't write any javadoc comments, as they are also inherited since java 1.4.

Brackets

All brackets should begin at the end of the line that begins the statement, and end on a new line indented to the beginning of the statement. Example:

AVOID:

public class MyClass 
{

    public void someMethod() 
    {
        if (...) { // Do something }
}
}

RIGHT:

public class MyClass {

    public void someMethod() {
        if (...) {
          // Do something
        }
    }
}

Brackets are mandatory even for single line statements:

if (expression)       // AVOID!
    // some code

if (expression) {     // RIGHT
    // some code
}

Blank Spaces

Keywords followed by a parenthesis should be separated by a space. Example:

while (true) {
    // some code
}

Blank space should appear after commas in argument lists. Binary operators should be separated from their operands by spaces:

a += c + d;
a = (a + b) / (c * d);

while (d++ = s++) {
    n++;
}

printSize("size is " + foo + "\n");

Class variables

Class variables should not have any prefix or suffix related to its data type or scope. Example:

String nameString;   // AVOID!

String name;         // RIGHT

Parameter names

Method parameters should be prefixed by "the" for differentiating them from inner variables, when there is an inner variable with the same name or use. For example:

public void someMethod(String theClassName) {
    String className; // inner variable
}

Line length

Avoid lines longer than 80 characters for Code, comments, ...

Versioning

All .java files should have a @version tag like the one below into the class javadoc comment:

@version $Id$

Logging

Do not use System.out to log. Instead, use the SLF4J logging API. For example:

private static final Logger LOG = 
    LoggerFactory.getLogger(MyClass.class);

public void someMethod() {
    LOG.debug("some debug text");
}

For more information on SLF4J usage, you can read the Logging document.

Exception handling

Managing exceptions correctly requires experience. This is not supposed to be a guide on managing exceptions, simply a few best practices.

• Rule 1: Try to catch exceptions as much as possible and rethrow higher level exceptions (meaning hiding the low level detailed and putting a message that is more related to the function of your code).
• Rule 2: It is important not to loose the stack trace which contains important information. Use chained exceptions for that.
• Rule 3: Always log the exception at the higher level (ie. where it is handled and not rethrown).
• Rule 4: Try to avoid catching Throwable or Exception and catch specific exceptions instead.
• Rule 5: Create one parent Exception for each API library, so methods of the API that throw any exception use that parent exception or one of the child ones.
• Rule 6: If you have an exception or an error which can't be handled or resolved by code, throw or rethrow a BaseRuntimeException subclass.

An example:

public void getTestClass() {
    try {
        Class responseClass =
            Class.forName("some.package.MyClass");
    } catch (ClassNotFoundException cnfe) {
        String message = "Cannot instantiate test class";
        LOG.error(message, ex);
        throw new ChainedRuntimeException(message, e);
    }
}

Qualified imports

All import statements should containing the full class name of classes to import and should not use the "*" notation: An example:

// AVOID!
import java.util.*;
import java.net.*;

// RIGHT
import java.util.Date;
import java.net.HttpURLConnection;

Use interfaces in the declaration of methods and variables.

By example, if you need a variable x that is a list, declare it as List instead an ArrayList:

// AVOID!
ArrayList x = new ArrayList();
HashMap y = new HashMap();

public HashMap create(ArrayList keys, ArrarList values) {
    ...
}

// RIGHT
List x = new ArrayList();
Map y = new HashMap();

public Map create(List keys, List values) {
    ...
}

API packages

Usually, API interfaces and classes will belong to the library's main root package. If you create subpackages, use them to group by functionality, not by type.

How to name packages

All packages must begin with org.gvsig.

For more information on this convention, you can read the How to name packages document.