Common code smells

Type codes and switch statements are common code smells. In addition, there are quite some other code smells that are also very common. Below is a summary list:

- Duplicate code.
- Too many comments.
- Type code.
- Switch or a long if-then-else-if.
- Cannot give a good name to a variable, method or class.
- Use names like XXXUtil, XXXManager, XXXController and etc.
- Use the words "And", "Or" and etc. in the name of a variable, method or class.
- Some instance variables are not always used.
- A method contains too much code.
- A class contains too much code.
- A method takes too many parameters.
- Two classes are using each other.