LCC 6310 Computation as an Expressive Medium

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LCC 6310Computation as an Expressive Medium

• Lecture 8

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Outline

• Programming concepts
• Processing Java-mode (programming in raw java)
• Introducing Parsing HTML
• HTMLEditorKit.ParserCallback
• HTMLReader
• Discuss reading
• Mythinformation

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Java Mode

• Allows you to program in pure Java
• Lets you import classes that arent normally
  imported into a Processing app
• Importing means making a classes available to
  your program the Java API docs tell you what
  package classes are in so you know what to import
• To go into Java mode, create a class that extends
  BApplet
• Normally all Processing applets extend BApplet
  behind the scenes
• Take at any compiled Processing app
• So, those top-level functions that werent
  methods of any class really are methods of a
  class, a class extending BApplet
• setup(), loop(), etc. are methods of the class
  extending BApplet

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Template of a Java-mode program

• class MyProgram extends BApplet
• void setup()
• void loop()
• void myTopLevelMethod()
• class Text // Text is just an example
• int xPos, yPos
• String word
• Notice that any classes you define are inside the
  top class

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Why use Java-mode again?

• Java-mode gives you access to the entire Java SDK
• We need access to some SDK classes for HTML
  parsing that Processing doesnt make visible by
  default
• Java-mode helps you to understand how Processing
  is built on-top of Java
• All those magic functions and variables are
  just methods and fields of BApplet that your
  program inherits

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What do you mean parse HTML?(and why would you
want to do it?)

• Parsing means to walk through the structure of
  a file (not just look at it character-by-character
  , word-by-word)
• Look at an HTML file
• The structure of an HTML file is the tag
  structure
• So parsing means to walk through and interpret
  the tags
• If you can parse HTML files, that means you can
  pull content out of web pages and do stuff with
  it
• Procedural manipulation of web content

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Basic approach

• Use two classes to parse
• One class reads info from a URL HTMLParser
• The other class is used by HTMLParser to process
  tags child of HTMLEditorKit.ParserCallback
• HTMLParser recognizes when a tag appears (ltTAGgt)
  and calls appropriate methods on the
  ParserCallback class (start-tags, end-tags,
  simple-tags, text, etc.)
• The programmer (ie. you), fill in the
  ParserCallback methods to do whatever you want
  when you see different kinds of tags

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Running the example

• Weve written HTMLParser for you
• To access it, it must be in the data directory of
  your project
• Simplest thing will be just to copy the code from
  the website and put the directory in your default
  sketchbook directory

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handleSimpleTag

• public void handleSimpleTag(HTML.Tag tag,
  MutableAttributeSet attrib, int pos)
• Called for tags like IMG
• tag stores the name of the tag
• attrib stores any attributes
• pos is the position in the file
• Example ltimg srcimage.gif alttext
  description of image alignright width10gt
• The tag is img
• The attributes are src, alt, align, width (with
  their respective values)

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handleStartTag

• public void handleStartTag(HTML.Tag tag,
  MutableAttributeSet attrib, int pos)
• Called for tags like BODY
• tag stores the name of the tag
• attrib stores any attributes
• pos is the position in the file
• Example ltbody bgcolorFFFFFF topmargin0
  leftmargin0 marginheight0 marginwidth0gt
• The tag is body
• The attributes are bgcolor, topmargin,
  leftmargin, marginheight (with their respective
  values)

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handleEndTag

• public void handleEndTag(HTML.Tag tag, int pos)
• Called for tags like lt/agt
• tag stores the name of the tag
• pos is the position in the file

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handleText

• public void handleText(char data, int pos)
• Handles anything thats not a tag (the text
  between tags)
• data is an array of characters containing the
  text
• pos is the position

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Filling in these methods

• You fill in these methods to do whatever
  processing you want
• In the image collage example
• handleSimpleTag is looking for images
• handleStartTag is looking for the start of
  anchors and follows links