Lecture Set 16 Command Line Running Issues Comments Command line Java Arguments to Main Method Commenting Review 1 2 3 CMSC 131 Spring 2008 Jan Plane adapted from Bonnie Dorr Command Line Java Source File an ASCII text file named appropriately for the class it contains i e ClassDemo java created by an editor emacs vi edit notepad Translate to byte code javac ClassDemo java creates a file named ClassDemo class Run and interpret the Byte Code java ClassDemo runs the java application defined in the the ClassDemo file Finding Things For the System to be able to find javac and java Command Search Path must be set it is named PATH For the System to be able to find the class named as the argument to the java command The Class Search Path must be set it is named CLASS PATH Both of these are set in Windows using the Control Panel System Advanced Environment Variables In Class Demonstration CMSC 131 Spring 2008 1 Jan Plane adapted from Bonnie Dorr Arguments to main Recall prototype of main method public static void main String args args is array of Strings args come from operating system Demonstration from Command Line When user runs executable s he can provide arguments simple arguments treating arguments as integers Demonstration from within Eclipse CMSC 131 Spring 2008 Jan Plane adapted from Bonnie Dorr 2 1 Types of Documentation Two kinds of code commentary in Java JavaDoc Implementation comments Interface comments from inside Eclipse from outside of Eclipse Common Errors in Commenting Too many comments This can obscure the flow of your program Too few comments Your intent may not be understood code is never self documenting Comments that repeat the code int total 0 initialize integer total to 0 Using comments to conceal unclear code just rewrite the code double a h w set the area a to the height h times width w double area height width Uninformative comments What the heck does that mean double d processValue Change later legacy Misleading erroneous comment These are dangerous for int i 0 i a length 1 i run through the whole array CMSC 131 Spring 2008 Jan Plane adapted from Bonnie Dorr 3 Javadoc Documentation Class comments Immediately prior to each public class add a javadoc comment that explains what the class does You can also add the following special tags which javadoc recognizes and provides special formatting for author the author of the class version the current software version number see refer the reader to related classes Example In Rational java Sample javadoc class comment This class implements a rational number object and provides methods for performing arithmetic on rational numbers see java lang Math author Schultzie von Wienerschnitzel III version 3 14159 public class Rational CMSC 131 Spring 2008 Jan Plane adapted from Bonnie Dorr 4 Javadoc Documentation Method comments Immediately prior to each public method add a javadoc comment explaining what the method does the meanings of the parameters the return value and any errors The following tags are recognized param give the name and description of each parameter There should be one for each parameter return describe the return value unless it is void throws Later we will discuss error exceptions later this semester deprecated Usually for system use indicates that a method should be avoided since better alternatives exist Example Sample javadoc method comment Multiplies two rational numbers and returns their the product param q The first operand param r The second operand return A reference to a newly created Rational with the sum public static Rational multiply Rational q Rational r CMSC 131 Spring 2008 Jan Plane adapted from Bonnie Dorr 5 2
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