1. Common Coding Defects

2. Agenda
Baby defects
Web Applications Common Defects

3. Baby Defects (1)
Do not string concatenated in loop, use StringBuffer instead
//Wrong example:
String stNumber = "";
for(i=0; i<100; i++) {
stNumber = stNumber + i; }
// Correct one
StringBuffer stBuf = new StringBuffer();
for(i=0; i<100; i++) {
stNumber.append(i);
}      
String stNumber = stBuf.toString();

4. Baby Defects (2) Do not get size of array in for statements condition
// Wrong example:
for(i=0; i<arrTemp.size(); i++) {
// do smt here }
// Correct answer:
int intSize = arrTemp.size();
f or(i=0; i<intSize; i++) {
// do smt here }

5. Baby Defects (3) // Wrong example: : if(stVariable.equals(“”)){ }
Compare a string with a constant, always call equals function from constant to avoid null pointer exception error.
// Wrong example: :
if(stVariable.equals(“”)){
// do smt here }
// Correct answer:
int intSize = arrTemp.size();
if(“”.equals(stVariable){
// do smt here }

6. Baby Defects (4) // Wrong : for(i=0; i<intSize; i++){ }
Avoid select from database to check for existing of values in a loop, this will increase system performance.
// Wrong :
for(i=0; i<intSize; i++){
// select database to check here }
// Select database, put to a HastTable object or List object. Remember Hastable object do not allow duplicate value :
for(i=0; i<intSize; i++){
// select the HastTable to check here }

7. Baby Defects (5) // Wrong : for(i=0; i<intSize; i++){ }
Do not create object in loop.
// Wrong :
for(i=0; i<intSize; i++){
TableRow objTable = (TableRow) vtResult.getElementAt(i);
// do smt here }
// Correct:
TableRow objTable = null;
for(i=0; i<intSize; i++){
objTable = (TableRow) vtResult.getElementAt(i);
// do smt here }

8. Baby Defects (6) // Wrong:
Use toString() function instead of typecast.
// Wrong:
String stTemp = x==y ? “” : objABC.toString();
// Correct:
String stTemp = x==y ? “” : (String)objABC;

9. Baby Defects (7) // Wrong: String stTemp = Integer.toString(i);
Redundant typecast
// Wrong:
String stTemp = Integer.toString(i);
// Correct:
String stTemp = “” + i;

10. Baby Defects (7) // Wrong:
Check for null before use objects to avoid null pointer exception
// Wrong:
String stAction = request.getAttribute("stAction").toString();
// Correct:
String stAction = request.getAttribute("stAction")==null ? "" :request.getAttribute("stAction");

11. Baby defects (8) SQL Injection (1) Lack of checking for null value(1)
public bool IsValidLogin(string userName, string password) {
SqlConnection con = null;
SqlCommand cmd = null;
bool result = false;
try {
con = new SqlConnection(DB_CONNECTION);
con.Open();
string cmdtext = string.Format("SELECT * FROM [Users] WHERE [Account]='{0}' AND [Password]='{1}' “, userName, password);
cmd = new SqlCommand(cmdtext);
cmd.Connection = con;
cmd.CommandType = CommandType.Text;
result= cmd.ExecuteReader().HasRows;
cmd.Dispose();
con.Dispose();
return result; }
catch (SqlException)
{return false;} }
SQL Injection (1)
Lack of checking for null value(1)
SQL Performance Issue !!(2)
Memory leak !! (2)

12. parameters as the same time
Baby Defects(9)
Combine function calling and passing
parameters as the same time
Assign value of the called function to a temp variable instead of pass it directly to the calling function, for example, instead of:
a = func1(func2(func3, func4));
you can use three temp variables:
b=func(3);
c=func(4);
d=fun2(b,c);
a=fun1(d);
When you use the temp variable, the code are clearly, and you can avoid the long line same as:
strReturn = objDoc.SelectNodes(objNode.Attributes(objAttr.ChildNodes.Item(0).ToString()));

13. Baby defects (10) Hardcode constant
-Give a fixed value when you format data, for example:
dgrView.PageSize = 10;
-Fixed error message in code
strErr = "Error message here";
-The problem occurs when you should change these values. If you put them in the constant file, you need change only one time, if you fixed them, you'll be find and change anywhere you have the fix value

14. Baby defects (11) Method can not be tested
public void aMethod( object arg) {
try {
\\ CODE BLOCK HERE }
catch (Exception) {
\\ DO NOTHING

15. Web Applications Common Defects
Alignment of fields, texts
Description
- The texts are not vertically left or right aligned.
- The fields are not vertically left and right aligned.
- All text should be left-justified
- All numeric fields are right-justified
Cause
There is no GUI template
Preventive action
Use CSS Style Sheet and GUI template

16. Web Applications Common Defects
Layouts in all pages
Description
All windows and dialog boxes don't have a consistent look and feel. Following items are not the same:
- Font of text
- Color and Background
- Header and footer
- Size of Logo
- Date format
Cause
There is no GUI template
Preventive action
Use CSS Style Sheet and GUI template

17. Web Applications Common Defects
Symbol for mandatory fields
Description
There is no symbol for mandatory fields to remind users.
Cause
Coding careless
Preventive action
Use template

18. Web Applications Common Defects
The buttons don't have the same height and distances
Description
The height of buttons and the distances between them in a page and in all pages are not the same
Cause
Graphic design
No GUI template
Preventive action
Use CSS Style Sheet and GUI template

19. Web Applications Common Defects
Data in combo box, list box
Description
Data in combo box/ list box is not sorted
Cause
Coding careless
Preventive action
Use checklist

20. Web Applications Common Defects
Different browses
Description
The layout in all required browses is not correctly (e.g. in Netscape, the alignment, the distances, positions of images … are not correct as in IE)
Cause
Non compatibility between IE , FireFox and Netscape…
Preventive action
- Use CSS Style Sheet
- Should clarify earlier when we get the requirement from the customer
- Simple pages should be used more frequently

21. Web Applications Common Defects
Cannot move between fields by using Tab key and Shift +Tab keys
Description
Users cannot use Tab key to move to next enterable fields and Shift + Tab keys to previous enterable fields.
Cause
Not set Tab index
Preventive action
Set Tab index

22. Web Applications Common Defects
Cursor location
Description
- The cursor is not located in the first enterable field when the screen is opened.
- After an error message occurs, the focus does not return to the error field.
Cause
Not focus on load
Preventive action
Set focus

23. Web Applications Common Defects
Images with links have blue borders
Description
Should hide the color of border of the image.
Cause
Coding
Preventive action
Set border properties = 0

24. Web Applications Common Defects
Incorrect links or the link does not work
Description
The links are not correctly. After clicking the links, error page or wrong page is displayed.
Cause
Coding
Preventive action
- Use tool to test broken links
- Use global variables to control
- Directly links need to be coded by experienced developers

25. Web Applications Common Defects
Using mouse and keyboard
Description
In general, everything can be done using both the mouse and the keyboard.
Cause
Not set focus
Preventive action
Set focus

26. Web Applications Common Defects
Error by input HTML tags, character '
Description
Should prevent errors when user inputs HTML tags or character ' in text fields. HTML tags can destroy the layout.
Cause
Careless, un-experienced coding
Preventive action
Use HTML Encode, URL Encode and SQL Encode

27. Web Applications Common Defects
Start date is greater than End date
Description
The logic of date is not checked, user can type Start date greater than End date, or From date is greater than To date…
Cause
Careless, un-experienced coding
Preventive action
Use checklist

28. Web Applications Common Defects
Users can return to Web application after logout
Description
- Users can back to previous page after logout by clicking "Back" button in Toolbars.
- When users logout, they cannot back to web application, and must input username and password again to login
Cause
Un-experienced coding
Preventive action
- Set cache of page = 0
- Re-set session variables
- Check session to assure that it is still active at the beginning of the page.

29. Web Applications Common Defects
Multiple users
Description
The application does not support many concurrent users as required.
Cause
Design/Coding
Preventive action
- Close connection immediately
- Optimize design, code
- Use tool to test

30. References
Refer Commons defects in attach folder

31. Q & A