Excerpts from Java Software Solutions 5th edition by Lewis&Loftus (Appendix F)
Method and variable names generally start with a lowercase letter and class names normally start with an uppercase letter. Identifiers are often a multi-word description of what they are identifying, and uppercase letters are used to specify word breaks. For example, a variable representing a first name might be called firstName. A class representing a bank account might be called BankAccount.
Code between an open brace ({) and the corresponding close brace (}) should be indented a consistent number of spaces. This applies to if statements, loops, method definitions, and class definitions. The close brace should always be lined up with the header of the statement. L&L suggest that the open brace be on a new line, however putting the open brace at the end of the header line is also common. Choose your own style, and be consistent!
Examples:
if(firstName.equals("Bob"))
{
//all code indented by the same amount
System.out.println("Short for Robert?");
System.out.println("Or is that your full name?");
}
public static void main(String[] args) { //open brace at the end of the header line
//all code indented by the same amount
System.out.println("Hello, world");
}
- Put one space after each comma in a parameter list.
- Put one space on either side of a binary operator.
- Do not put spaces immediately after a left parenthesis or before a right parenthesis.
- Do not put spaces before a semicolon.
- Put one space before a left parenthesis, except before an empty parameter list.
- Every source code file should contain a header block of documentation providing basic information about the contents and the author.
- Each class and interface, and each method in a class, should have a small header block that describes its role.
- Use in-line documentation as appropriate to clearly describe interesting processing.
- Don't wait until a program is finished to insert documentation. As pieces of your system are completed, comment them appropriately.
Beginning programmers are typically most concerned with getting their code to run. Just getting a program to compile can be such a huge hurdle that the programmer doesn't stop to think about whether someone else can actually read the code, or whether it can be easily extended to support new functionality. However, the process of designing a clean program is extremely important, and a good design can make the coding itself much simpler.
Becoming a good designer takes lots of practice, and it also takes a bit of confidence. As you design programs, you have to have confidence that you will be able to figure out a way to implement your designs. Rather than try to piece together what you know how to do, think about what you want your program to do and have confidence that you can find a way to make your program do that.
Additionally, understand that program design is a creative process. Your design for a program may differ from that of one of your classmates. You may also design a program and decide that your design isn't quite right. You need to be willing to redesign your programs when you discover that your design just doesn't support everything it needs to.
Design really is a creative process and each person may approach the process differently. For the purposes of this class, the outcome of the design process will be a set of classes you need to implement, the data and methods each class will contain, and and overview of how the classes will interact. Larger programs may have more complex design issues and the first outcome of the design process will be a system architecture with multiple components for which a more refined design will then be developed.
Keep in mind that an initial design is unlikely to be flawless. You will almost certainly need to go back and refine or change your design as you implement your program.
Class Responsibilities Collaborators (CRC) Model
The CRC model is an approach to design wherein the designers use index cards to represent the classes interacting in a program. For each class, the designers identify the responsibilities of the class and the classes with which it will need to collaborate in order to execute its responsibilities.
Links:
http://www.agilemodeling.com/artifacts/crcModel.htm
Unified Modeling Language (UML)
UML stands for the Unified Modeling Language, which has become the most popular notation for representing the design of an object-oriented program.
UML class diagrams represent each class with a rectangle, inside of which are the data members and methods supported by the class. Dotted arrows are drawn between classes to indicated that one class invokes the methods of another. There are many other types of UML diagrams as well.
Links:
http://dn.codegear.com/article/31863
Identifying Classes
The CRC model and UML help you to think through what each class should contain and how to relate one class to another. But, the question of how to identify an initial set of classes still remains. It is certainly worth your time to revisit Chapter 6 (particularly 6.1-6.4) of the L&L text.
One approach (discussed in the text) to identifying the classes you should use in your design is to identify the nouns and noun phrases present in the description of the program you must write. Below is a description of a Connect Four program. From this description, identify a set of classes you might use to implement the program. An example might be a class to represent the board.
The game is played using a board with 7 columns and 6 rows. Each player is assigned a color, one player is red and one player is black. At each turn, a player places a checker of her color in the top empty space of one of the columns. Once a checker has been placed, your program will check to see if a player has won the game, or if the board is full. A player wins if four checkers of her color are adjacent either vertically, horizontally, or diagonally. If there is a win or tie, the program will print an appropriate message and exit. If not, the next player takes a turn.
Links:
http://www.codeproject.com/gen/design/idclass.asp
Identifying Methods
Methods define the behaviors of each class. To identify the methods necessary for the program, consider the actions described by the verbs in your program description. In the example above, we would likely want to have a method to support placing a checker on the board. That might indicate that a placeChecker method should be implemented in the Board class.
It may not always be clear in which class a method should be implemented. Again, don't be afraid to consider multiple options and change your design if necessary.
Discussion:
Date: 2007-08-13