Wednesday, June 07, 2001

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CM245 Lecture 1
CM245 - Contemporary Programming Methods Lecture 2
Wednesday, June 07, 2001 Cecil P.
Schmidt Department of Computer Information
Sciences Washburn University Topeka, KS.
66621 zzschmid_at_washburn.edu
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Presentation Outline

• Syllabus
• Introduction to Java
• Chapter 1 of Bell Parr
• How to compile a Java program at Washburn
• Punch and run assignment

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Applets vs. Applications (Review)

• Applets are invoked as part of a Web page
• Applets cannot run alone. The must run with the
  aid of a browser.
• Applications are free standing programs
• Applications require the main method
• example Hello.java

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How Do You Build a Java Program

• Text Editor with Java Development Kit (JDK)
• Integrated Development Environments (IDE)
• VisualAge Java
• Visual J
• JBuilder
• An IDE is great for large applications, screen
  painting and debugging. Its best to learn
  without one first.
• We are not using an IDE for this class. We are
  using the text editor option.

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Files and Directories

• Java source file ltfilename.javagt
• Java object file ltfilename.classgt
• Typical data file ltfilename.datagt
• Directory contains a set of (related) files

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Edit-Compile-Execute Process

• Edit build a .java file using either an IDE or
  an editor
• Compile converts .java to .class (byte code)
• Execute run the .class file with the JVM

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Creating and running an applet

• HelloApplet.java
• Using the appletviewer utility
• Moving the file to your web site after testing

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Chapter 3 - Introduction to graphics

• Drawing a line on a graphic object
• g.drawLine(0,0,100,100)
• g is a graphic object which is automatically
  created for you because your program ISA applet
  and all applets have access to a method call
  paint and a graphics object!
• drawLine is method that comes with a graphics
  object
• The graphics screen
• Java graphics based on pixels
• A pixel is a small dot on the screen which can
  accessed.
• Different screens have different pixel counts
• In HTML we can define the initial pixel width and
  height
• A pixel is identified by a pair of numbers
  (coordinates) starting at zero
• (x,y) x horizontal position (increases left to
  right)
• y vertical position (increases top to bottom)

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The FirstLine Program

• An explanation of the program
• g.drawline(0,0,100,100)
• g.drawline(xStart,yStart,xEnd,yEnd)
• where xStart, yStart, xEnd, yEnd are know as
  parameters (arguments) in java,
• g is the name of the object
• drawline is the method name (same as function)
• note the semicolons and not all methods require
  arguments
• The paint method
• This method must be written by the programmer in
  support on an applet
• For our purposes now, we will assume that this is
  the first method that runs in our applet.

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Other methods used for drawing

• Lets find the Graphics object and see what it has
  to offer!
• The Graphics class is a member of the AWT
  library.
• void drawLine(int x1, int y1, int x2, int y2)
• Draws a line, using the current color, between
  the points (x1, y1) and (x2, y2) in this graphics
  context's coordinate system
• void drawRect(int x, int y, int width, int
  height)
• Draws the outline of the specified rectangle.
• void fillOval(int x, int y, int width, int
  height)
• Fills an oval bounded by the specified rectangle
  with the current color.
• void drawArc(int x, int y, int width, int height,
  int startAngle, int arcAngle)
• Draws the outline of a circular or elliptical arc
  covering the specified rectangle

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Filling shapes and setting colors

• setColor
• fillRect
• fillArc
• fillOval
• The FirstShapes.java program
• Displaying characters on a graphic
  object g.drawString("Hello CM245 class",30,40)
• Joining strings with

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Exercises

• PunchRun 2 (Lab 2)
• Data Visualization Exercise
• See course web site for complete write-up