Debugging

1
Debugging

• Chapter 5 (ALBINGs)
• Section 4.3 (ALBINGs)
• Section 4.4 (ALBINGs)

2
FetchURL example

• Assert post-conditions in right place when you
  have conditions
• You can use the URL class to
• Download an HTTP document from a Web server. This
  document can be a static file or can be
  dynamically constructed by the Web server
• Send an e-mail message
• A URL has four parts
• Protocol name
• Host address
• Port (80 by default for http)
• port number to which the TCP connection is made
  on the remote host machine
• Path to resource file
• http//java.sun.com80/index.html

3
URL to Read Web Pages

• When you start the client connects to a Web
  server. In the client code, you
• Create a URL object
• Import java.net.
• URL x new URL(http//www.google.com)
• URL y new URL(mailtoirahal_at_csbsju.edu)
• Create an InputStream object from the URL object
• X.openStream()
• Shortcut for x.openConnection().getInputStream()
• opens a connection to the server and allows us to
  read its response to our clients request (get
  page)
• Returns an InputStream object which we pass to
  the InputStreamReader to convert bytes to
  characters
• Then pass result to BufferedReader so that we can
  read it one line at a time
• BufferedReader rdr new BufferedReader(new
  InputStreamReader( x.openStream())
• BufferedReader rdr new BufferedReader(new
  InputStreamReader( x.openConnection().
  getInputStream()))

4
FetchURL example

• while ((line rdr.readLine()) ! null)
• Why do we see HTML?
• Because we are not using a browser so we output
  the HTML tags as is

5
URL to Send EMails

• Before starting, client must connect to a mail
  server, such as sendmail
• Create a URL object
• System.getProperty("mail.host",
  "unix.csbsju.edu")
• URL doesn't contain any information about the
  mail server ? need to specify it explicitly by
  setting a Java system property
• "unix.csbsju.edu is the default in case non is
  found
• URL url new URL("mailtoirahal_at_csbsju.com")
• Create a URLConnection object
• url.openConnection()
• Returns a URLConnection object that represents a
  connection to the remote object referred to by
  the URL
• Create an OutputStream object from the URL object
• PrintStream out new PrintStream(url.openConnect
  ion(). getOutputStream(), true)
• Write the mail using out object
• Close out
• A connection to a server is required for these
  actions

6
list

• main1 list
• 31
• 32 e.printStackTrace()
• 33 rc null
• 34
• 35 gt return line.toString()
• 36 //return rc
• 37
• 38
• 39 public String callToString()
• 40
• main1

7
locals

• main1 locals
• Method arguments
• Local variables
• rc "lt!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML
  3.2//EN"gt
• ltHTMLgt
• ltHEADgt
• ltMETA NAME"Generator" CONTENT"Cosmo Create
  1.0.3"gt
• ltBASE HREF"http//www2.csbsju.edu/index.html"
  gt
• ltTITLEgtCollege of Saint Benedict and Saint
  John's Universitylt/TITLEgt
• ltlink REV"made" HREF"mailtoadmissions_at_csbsj
  u.edu"gt
• ltmeta HTTP-EQUIV"Content-Type"
  CONTENT"text/html charsetISO-8859-1"gt
• ltmeta HTTP-EQUIV"Content-language"
  CONTENT"en"gt
• ltmeta HTTP-EQUIV"Reply-to"
  CONTENT"admissions_at_csbsju.edu"gt
• . lt/HTMLgt
• "
• line null
• rdr null

8
Navigating the call chain

• main1 where
• 1 FetchURL.toString (FetchURL.java35)
• 2 FetchURL.callToString (FetchURL.java41)
• 3 FetchURL.main (FetchURL.java51)
• main1 up (go up the caller of 1 which is
  2)
• main2 locals
• No local variables
• main2
• main2 up (go up the caller of 2 which is 3)
• main3 locals
• Method arguments
• args instance of java.lang.String1 (id424)
• Local variables
• i 0
• f instance of FetchURL(id425)
• main3

9
Finding the call site in main

• main3 list
• 47 for (int i 0 i lt args.length
  i)
• 48
• 49 System.out.println(argsi
  " ")
• 50 f new
  FetchURL(argsi)
• 51 gt System.out.println(f.callToS
  tring())
• 52
• 53
• 54
• 55
• main3

10
Examining Values

• main3 dump f
• f requestURL instance of java.net.URL(id426)
  
• main3 dump i
• i 0

11
More Navigation

• main3 down
• main2 down
• main1
• main1 exit

12
System Properties

• GetMailURL.java
• //enumerates over a collection of objects
• Enumeration enm System.getProperties().propertyN
  ames()
• while (enm.hasMoreElements())
• String propName (String) enm.nextElement()Sys
  tem.out.println(propName""System.getProperty(pr
  opName))
• Output
• java.runtime.nameJava(TM) 2 Runtime Environment,
  Standard Edition
• sun.boot.library.path/usr/local/jdk1.5.0/jre/lib/
  i386
• java.vm.version1.5.0-b64
• java.vm.vendorSun Microsystems Inc.
• java.vendor.urlhttp//java.sun.com/
• path.separator
• java.vm.nameJava HotSpot(TM) Client VM

13
System Properties

• file.encoding.pkgsun.io
• user.countryUS
• sun.os.patch.levelunknown
• java.vm.specification.nameJava Virtual Machine
  Specification
• user.dir/usr/people/faculty/cs/irahal/csci230bin/
  FetchURL
• java.runtime.version1.5.0-b64
• java.awt.graphicsenvsun.awt.X11GraphicsEnvironmen
  t
• java.endorsed.dirs/usr/local/jdk1.5.0/jre/lib/end
  orsed
• os.archi386
• java.io.tmpdir/tmp
• line.separator
• sun.cpu.isalist

14
System Properties

• java.vm.specification.vendorSun Microsystems
  Inc.
• os.nameLinux
• sun.jnu.encodingUTF-8
• java.library.path/usr/local/jdk1.5.0/jre/lib/i386
  /client/usr/local/jdk1.5.0/jre/lib/i386/usr/loca
  l/jdk1.5.0/jre/../lib/i386/usr/local/fortran/lib
  /usr/local/oracle/lib
• java.specification.nameJava Platform API
  Specification
• java.class.version49.0
• sun.management.compilerHotSpot Client Compiler
• os.version2.6.9-34.0.1.ELsmp
• user.home/usr/people/faculty/cs/irahal
• user.timezone
• java.awt.printerjobsun.print.PSPrinterJob
• file.encodingUTF-8
• java.specification.version1.5
• user.nameirahal
• java.class.path/usr/people/faculty/cs/irahal/Java
  Packages/usr/people/classes/Java/mysql-connector-
  java-3.1.10-bin.jar/usr/people/classes/Java/objec
  tdraw/objectdraw.jar/usr/people/classes/Java.

15
System Properties

• java.vm.specification.version1.0
• sun.arch.data.model32
• java.home/usr/local/jdk1.5.0/jre
• java.specification.vendorSun Microsystems Inc.
• user.languageen
• java.vm.infomixed mode, sharing
• java.version1.5.0
• java.ext.dirs/usr/local/jdk1.5.0/jre/lib/ext
• sun.boot.class.path/usr/local/jdk1.5.0/jre/lib/rt
  .jar/usr/local/jdk1.5.0/jre/lib/i18n.jar/usr/loc
  al/jdk1.5.0/jre/lib/sunrsasign.jar/usr/local/jdk1
  .5.0/jre/lib/jsse.jar/usr/local/jdk1.5.0/jre/lib/
  jce.jar/usr/local/jdk1.5.0/jre/lib/charsets.jar/
  usr/local/jdk1.5.0/jre/classes
• java.vendorSun Microsystems Inc.
• file.separator/
• java.vendor.url.bughttp//java.sun.com/cgi-bin/bu
  greport.cgi
• sun.cpu.endianlittle
• sun.io.unicode.encodingUnicodeLittle

16
System Properties

• Still leaves out so many other properties
  (environment variables)
• Security reasons !

17
The Eclipse IDE

• Section 10.4 (ALBINGs)
• http//help.eclipse.org/help32/index.jsp

18
Introduction

• Eclipse is a generic, extensible, open source IDE
  (integrated development environment)
• completely platform- and language-neutral
• diverse mix of languages supported by the Eclipse
  (Java, C/C, Cobol)
• projects underway to add support for languages as
  diverse as Python, Eiffel, PHP, Ruby on Rails,
  and C to Eclipse
• The project was originally launched in November
  2001, when IBM donated 40 million worth of
  source code from WebSphere Studio Workbench
• Eclipse includes a number of unique features such
  as
• code refactoring
• support for unit testing with JUnit

19
Eclipse Workbench

• Perspective Switcher
• Toolbar
• Editor Area
• Views
• If you close any of the views and would like to
  reopen it
• Windows gt Show View gt select it

20
Perspectives in Eclipse

• Click on the Perspective Switcher and select the
  Java perspective
• Each perspective defines a selection of views and
  their layout within the workbench window
• Each is configured for a particular task such
  Java development, debugging, etc
• Windows gt Open Perspective gt Java
• Other perspectives
• Resource useful for browsing your workspace
• Java
• Debug
• CVS Repository Exploring used for exploring CVS
  repositories
• Etc

21
Wizards

• Look at the middle of your toolbar
• New Java Project
• New Java Package
• New Java Class
• Others

22
Create a New Project

• Click on the New Java Project wizard
• Enter a qualified name
• It is common to use qualified names for projects
  in the Eclipse Workspace
• This reflects the primary Java package contained
  in each Project
• edu.csbsju.catalogue
• Insures unique self-describing names for projects
  shared in a source control repository such as CVS
• It is advisable that you check the Create
  separate source and output folders
• Creates a src folder for source code and bin
  folder for complied class files

23
Create a New Package

• Select the project folder in the Package Explorer
• A Java project folder is indicated by an open
  folder icon with an overlaid J
• Click the New Java Package wizard to create a new
  Java Package
• Enter the package name
• edu.csbsju.catalogue
• Within the workspace directory on your file
  system, three nested directories are created
  inside the project folder
• edu
• csbsju
• catalogue

24
Create a New Class

• Select the created package in the src folder in
  the Package Explorer view
• A Java package is indicated by an icon resembling
  a box wrapped with a string
• Enter class name, Catalogue
• Notice the options for creating inner classes,
  specifying a superclass, implementing interfaces,
  and generating method stubs and comments

25
Customizing Code Templates

• Window gt Preferences
• Java gt Code Style gt Code Templates
• Code gt New Java files
• Comments gt Types
• Delete and recreate class

26
Compile Run

• Redo Catalogue and CatalogueItem example from
  Eclipse Distilled by Carlson
• Compile is done while creating code!
• How do I choose my own compiler?
• Window gt Preferences gt Java gt Compiler
• To run using the Console view
• Windows gt Show View gt Console
• From Package Explorer, right click Class to run
  and select Run gt Java Application
• When moving to a new project, make sure you close
  the first one first
• File gt Close All

27
Run a Project with Command-line Arguments

• In Package Explorer
• Select file to run
• Click on Run gt Run
• Or Right click file and Run As gt Run
• Go to Arguments Tab and provide arguments each on
  a separate like
• Click on Run

28
Import a Project to Eclipse

• Create a new project
• Type project name
• Select Create project from existing source
• Browse and select your project folder
• Under Default output folder
• Browse
• Click on the Project Name
• Create a new Folder called bin
• Now your project works as if it has been created
  within Eclipse but it may not be under your
  workspace

29
Switching Workspaces

• I started eclipse but I dont see any of my
  projects !
• You can Switch Workspace to default location
• In the Java perspective, File gt Switch Workspace
• If the above doesnt work, then, in the Package
  Explorer, right click and Import
• Select Existing Projects into Workspace

30
Multiple Workspaces

• By default, all projects are stored in your
  default workspace (/Eclipse)
• If you create a new workspace then you might need
  to switch between them
• In the Java perspective, File gt Switch Workspace

31
Generating Getters and Setters

• Generating Code
• Getters and Setters
• Right click in the editor
• Select Source
• Generate Getters and Setters
• Constructor
• Right click in the editor
• Select Source
• Generate Constructor