Command Line Running Issues & Comments

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 inter pret 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

Arguments to main

Recall prototype of main method
public static void main (String[ ] args);

args is array of Strings
args come from operating system
When user runs executable …
… s/he can provide arguments

Demonst ration from Command Line

simple arguments
treating arguments as integers

Demonstration from within Eclipse

Types of Documentation

Math -software/how-to-multiply-two- square -roo.html">Two kinds of code commentary in Java

Implementation comments
Interface comments

JavaDoc

from inside Eclipse
from outside of Eclipse

Common Errors in Commenting
Too many comments: This can obscure the f low 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 / err oneous comment : These are dangerous
for ( int i = 0; i < a.length-1; i++) // run through the
//whole array

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 /** * 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 { … }

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:

/**

* 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) { … }