1CMSC 131 Spring 2008Jan Plane (adapted from Bonnie Dorr)Lecture Set #16:Command Line Running Issues & Comments1. Command-line Java2. Arguments to Main Method3. Commenting ReviewCMSC 131 Spring 2008Jan Plane (adapted from Bonnie Dorr)1Command-Line JavaSource 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.javacreates a file named ClassDemo.classRun (and interpret the Byte Code):java ClassDemoruns the java application defined in the the ClassDemo fileFinding ThingsFor the System to be able to find javac and javaCommand Search Path must be set it is named PATHFor the System to be able to find the class named as the argument to the java commandThe Class Search Path must be set it is named CLASS PATHBoth of these are set in Windows using the Control Panel/System/Advanced/Environment VariablesIn Class Demonstration2CMSC 131 Spring 2008Jan Plane (adapted from Bonnie Dorr)2Arguments to mainRecall prototype of main methodpublic static void main (String[] args);args is array of Stringsargs come from operating systemWhen user runs executable …… s/he can provide argumentsDemonstration from Command Linesimple argumentstreating arguments as integersDemonstration from within EclipseCMSC 131 Spring 2008Jan Plane (adapted from Bonnie Dorr)3Types of Documentation Two kinds of code commentary in JavaImplementation commentsInterface comments JavaDocfrom inside Eclipsefrom outside of EclipseCommon Errors in CommentingToo 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 0Using comments to conceal unclear code: …just rewrite the codedouble 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 dangerousfor ( int i = 0; i < a.length-1; i++) // run through the //whole array3CMSC 131 Spring 2008Jan Plane (adapted from Bonnie Dorr)4Javadoc DocumentationClass 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 classesExample: In Rational.java/*** 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 { … }Sample javadocclass commentCMSC 131 Spring 2008Jan Plane (adapted from Bonnie Dorr)5Javadoc DocumentationMethod 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. Thereshould 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 beavoided, since better alternatives exist)Example:/*** 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) { … }Sample javadoc method
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