1. 07 Coding Conventions

2. Objectives • Demonstrate Developing Local Variables • Describe Separating Public and Private Members during Declaration • Explore Using System.exit • Demonstrate Validating Method Arguments • Describe Using Testing Framework • Distinguish Checked Vs. Unchecked Exceptions • Describe File Organization

3. Coding Conventions: Resource • Reference the Coding Conventions.pdf file on the Module 2 section of the Sharepoint site. • This is a booklet published by Sun that contains all of the basic coding standards for Java. • It is easier to learn to follow coding standards early in your work with a programming language. • Familiarize yourself with the most basic coding conventions, and notice how Eclipse supports you in developing within these guidelines. • The remainder of this presentation will present more abstract but equally important “Best Practices” for coding.

4. Coding Conventions: Best Practices Declare local variables immediately before use • Defines their scope. • Decreases the likelihood of illegibility or error. Fields should be private • Declaring fields to be public is usually incorrect, it does not protect the user of the class from changes in class implementation. • Declare fields as private. If fields need to be accessed by the user of the class, provide the necessary get and set methods.

5. Coding Conventions: Best Practices Separate public and private members during declaration • It is a common practice to separate the members of a class according to their scope (private, protected, public) It is the choice of the programmer which will come first. Use Javadoc liberally • Javadoc is a great tool and should be used.

6. Coding Conventions: Best Practices Use System.exit(0) with care on multi-threading applications • System.exit should be used with care. The normal method of terminating a program is to terminate all user threads. Use interface for constants • Creating a class whose sole job is to define widely-used constants is simple.

7. Coding Conventions: Best Practices Validate method arguments • The first lines of a method are usually devoted to checking the validity of all arguments. The idea is to fail as quickly as possible in the event of an error. This is particularly important for constructors. Extra space in argument list • Some programmers feel that using extra spaces within parentheses - as in ( this ) instead of (that) - slightly increases the legibility of code.

8. Coding Conventions: Best Practices Use a testing framework • Use a testing framework to ensure your class fulfills its contract. Use zero-length arrays instead of null • If a method returns an array which can be empty, do not allow it to return null. Instead, return a zero-length array. • This simplifies the client, in that it never has to check for null values.

9. Coding Conventions: Best Practices Avoid empty catch blocks • It is not good to have an empty catch block. • When the exception occurs, nothing happens, and the program fails for unknown reasons. Be specific in the throws clause • In the throws clause of a method header, be as specific as possible. Do not group together related exceptions in a generic exception class – this could result in a loss of important information.

10. Coding Conventions: Best Practices Checked vs. Unchecked Exceptions Checked exceptions : • Represent invalid conditions in areas outside the immediate control of the program (invalid user input, database problems, network outages, absent files). • Are subclasses of Exception. • Methods are obligated to establish a policy for all checked exceptions thrown by its implementation (either pass the checked exception further up the stack, or handle it somehow).

11. Coding Conventions: Best Practices Checked vs. Unchecked Exceptions Unchecked exceptions : • Represent defects in the program (often invalid arguments passed to a non-private method). • Are subclasses of RuntimeException, and are usually implemented using: • IllegalArgumentException. • NullPointerException. • IllegalStateException. • Methods are not obligated to establish a policy for the unchecked exceptions thrown by their implementation.

12. Coding Conventions: Best Practices Choosing the right collection • Sun documentation refers to ArrayList, HashMap, and HashSet as being the preferred "primary implementations". Their overall performance is better, and should be used unless a special feature provided by another implementation is needed. These special features are usually ordering or sorting. • “Ordering" refers to the order of items returned by an Iterator, and "sorting" refers to sorting items according to Comparable or Comparator.

13. Coding Conventions: Best Practices Iterate without an index • Some programmers have a strong preference for using a for-each loop or an Iterator instead of indexed for-loops. Indexes have always been a major source of error, and should generally be avoided if there is an alternative.

14. Coding Conventions: Best Practices File Organization • Each Java source file contains a single public class or interface. When private classes and interfaces are associated with a public class, they can be placed in the same source file as the public class. • The public class should be the first class or interface in the file.

15. Coding Conventions: Best Practices Line Length • Avoid lines longer than 80 characters. They are not handled well by many terminals and tools. Variable Assignments • Avoid assigning several variables to the same value in a single statement. It is hard to read. • Example: fooBar.fChar = barFoo.lchar = 'c'; // AVOID!

16. Coding Conventions: Best Practices Declarations One declaration per line is recommended since it encourages commenting. Please Note: • int level; // indentation level • int size; // size of table is preferred over • int level, size; Do not put different types on the same line. Example: • int foo, fooarray[]; //WRONG!

17. Coding Conventions: Best Practices Statements Each line should contain only one statement. Example: • argv++; // Correct • argc--; // Correct • argv++; argc--; // AVOID!

18. Key Points • Learn the traditional formats for naming variables, methods and other components of coding in Java. • Notice the guidelines on indentation. • Remember that you will be working on projects in teams, and following these conventions and standards will help to make your work much more “readable” for the other members of your team. • Declare local variables immediately before use. • Avoid declaring or assigning values of more than one variable per line of code. • Fields should be private, with setters and getters if needed. • Use System.exit with care. • Use an interface for constants. • Validate method arguments. • Use a testing framework. • Use zero-length arrays instead of null. • Choose the best collection framework. • Iterate without an index.

19. Resources Helpful Websites: http://www.javapractices.com/index.cjp http://java.sun.com/docs/codeconv/html/CodeConvTOC.doc.html http://geosoft.no/development/javastyle.html http://www.infospheres.caltech.edu/resources/code_standards/java_standard.html http://www.ambysoft.com/javaCodingStandards.html