FrameEditorDemo

1
Lecture 4

• FrameEditorDemo
• Packages
• System Object
• Runtime Object
• File Systems

2

User
(JVM)
runs
Files
FrameEditorTester
creates
reads/writes
FrameEditor
GameFrame
creates
creates
quitButton
interacts with
User
3
Flow of ActionEvents
FrameEditorTester
?
FrameEditor
GameFrame
?
4
Effect of wrapper addActionListener methods
FrameEditorTester
initial calls to addActionListener()
FrameEditor
GameFrame
relayed calls to addActionListener()
5
Packages

• Hierarchy of classes, independent of
  inheritance.
• Packages group classes related by function.
• A package is a namespace
• protected/package access specifiers

6
Creating Packages

• First line of each file is
  package packagename
• To access a class import packagename.classna
  me
• To access all classes from a package import
  packagename.
• Each package has its own directory, named
  packagename.

7
Using Packages

• By default, files are in the unnamed package.
  This is only ok for very small projects.
• Can have hierarchies of packages. Ex
  com.company.region.package. This corresponds to
  the directory CLASSPATH/com/company/region/packag
  e. There are a few naming conventions.
• Separate import statements for each package,
  even subpackages.

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Example Package Layout
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File Layout
ActionFrame.java
(unnamed)
frameeditor
FrameEditor.java
app
pres
trans
EditorFrame EditorPanel EditorMenuBar IconSelector
HelpFrame EditorToolbar
FileSaver EditUndoer
TargetHandler EditorPanelHandler EditorMenuHandler
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Package code
frameeditor.FrameEditor
package frameeditor import ActionFrame import
frameeditor.pres. import frameeditor.app. impo
rt frameeditor.trans.
frameeditor.pres.EditorFrame
package frameeditor.pres import
ActionFrame import frameeditor.FrameEditor
frameeditor.trans.EditorMenuHandler
package frameeditor.trans import
ActionFrame import frameeditor.FrameEditor impor
t frameeditor.app. import frameeditor.pres.Edito
rMenuBar
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Package Details

• Matters where you compile from. Java and Javac
  look in 2 places for packages CLASSPATH, and
  the current directory.
• Java, Javac can find classes and directories
  stored in ZIP and JAR archives.
• May have to disambiguate names, e.g.
  javax.swing.Timer, java.util.Timer and
  com.thomasphayes.silly.Timer

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File Systems

• A standardized, high-level mechanism to allow a
  user or users to access organized data on a
  medium or media.
• Usually a rooted tree at heart (Unix), sometimes
  a rooted forest (Win), may be a directed graph
  (both fake this).
• Files, directories, paths.
• Permissions, owners, locks.

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Paths

• Steps from one node to another.
• May be absolute (starts at root), canonical
  (absolute, plus no redundancies or shortcuts), or
  relative (starts somewhere else).
• . current, .. parent, / or \
  file-separator, or path-separator.
• Root / in Unix. L\ in Win

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Warning File systems

• Notably, the pathnames for Win and Unix are
  different.
• Windows C\home\hayest\fname
• Unix /home/hayest/fname
• File location conventions also differ.
• JRE seems to support Unix symlinks but not
  Windows Shortcuts.

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Solutions

• java.io.File.separator
  Do not hard-code pathnames.
• Environment variables. HOME, PATH, CLASSPATH,
  FRAMEEDITORSAVEPATH, etc. Your installer
  can easily set up more.
• Make user locate files (JFileChooser)

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Example Fixing filenames

• images/starters/icon1.gif or
  images\\starters\\icon1.gif should be replaced
  by images file.separator starters
  file.separator icon1.gif
• Avoid symbolic links and absolute paths.
• e.g. images needs to be replaced by ..
  file.sep .. file.sep images file.sep
  starters in a number of the demos.

17
Environment variables

• Can get a few of these with System.getProperties(
  )
• Can get all from shell, but code will be highly
  system dependent. Runtime rt
  Runtime.getRuntime() Process proc
  rt.exec(set) //code to grab output from
  process
• Demo code

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RunTime and System

• System provides a system-independent way of
  accessing system resources, but is very limited.
• Runtime lets you execute OS commands, and fiddle
  with the Java Interpreter and Java Virtual
  Machine. You should minimize and encapsulate
  this code to retain some portability.

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The Runtime Object
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System calls

• Get the Runtime instance (there can be only
  one). Runtime rt
  Runtime.getRuntime()
• Call an exec method. This returns a Process
  object and may throw an IOException.
• Monitor the returned Process.

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Runtime Example

• Runtime.getRuntime() gets the Runtime object.
• exec() creates a Process object.
• Wrap the InputStream produced by the Process
  object, then use read() methods to read the
  input.
• waitFor(), destroy() methods available.

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Shells

• A tool for low-level OS control.
• High-level conveniences, such as variables, job
  control, automatic completion, scripting.
• Downside steep learning curve, ugly.
• Perfect candidate for a GUI!

23
Shell --gt WinDohs 101

• Goal Ability to open and close directories, and
  to view files and their properties.
• Shell normally lets you into only one directory
  at a time this doesnt make sense for our GUI.
  Each window can display the contents of a
  directory.
• When to refresh?

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Oh no!

• We must be experts at using the File, System,
  and Runtime objects.
• We must be experts on the shell.
• We must be experts on the OS.
• We must be experts on GUIs.
• We must be crazy!

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Dont Panic!

• Basically, our job is translation.
• The shell will do all the really hard work.
• Plenty of help out there for the asking.
• We have already learned most of what we need.

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User
(JVM)
runs
WinDohs
creates
creates
Runtime
DirectoryFrame
invokes
creates
creates
data
Process
interacts with
User
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create desktop bring up FolderSelector
click on directory name check permissions open
and refresh a new window if ok
FolderSelector
Cancel
click on refresh button or refresh timer
event. check permissions exec(ls) display
output if ok
QuitDialog
Quit
Done
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Summary

• Work on FrameEditor!
• Study the Demos
• Course Project Specs TBA this week