GVSU CS 162 Lecture-Module #02: Overview of Java Programming with Graphics

CS 162 Lecture-Module #02:
Overview of Java Programming with Graphics

"The Analytical Engine has no pretensions whatever to originate anything. [But] it can do whatever we know how to order it to perform."
: Ada Lovelace, the world's first computer programmer

programs operate in the context of a system

hence need framework

import java.awt...          ----+
                                |
public class Picture {          |
 .                              | ~~ignore this as much as possible
  .                             |    --- just copy as needed
   .                            |
                                |
    public void                 |
                draw() {        | <some main 'method'>
                            ----+
                            ----+
        .                       | <-- here is where you work
        .                       |     -==-
        .                       |     writing your program
                             ---+       --- list of instructions
         }

programming environment --- ~~significant part of framework
* type your program:  prog.java ,  prog.html
* basic editor such as  NotePad
or
* IDE such as BlueJ
* compile and execute i.e. run your program
* MSDOS / Command prompt
*  javac prog.java
*  appletviewer prog.html
or
* within IDE use menus etc. to request everything
* improve/debug your program:
* consider compilation-errors particularly the first one
e.g. if forget ";" at end of first  import-line
*  javac prog.java 2>&1  more
or things your program does differently from what you want
* re-edit your  .java file
* re-try compiling and executing
(* save and print your material)

<Picture>

Java coordinate-system:

        (0,0)    15                 horizontal
            +----+----------------------->
            |
            |
            |
            |
         25 +    
            |
            |
            |
         40 +    
            |
            |
vertical    V

positive
increasing
downward

(
NOT Cartesian coordinate-system where vertical coordinates increase upward:

    y ↑
      |
      |
      +--->
          x

)
a way to remember that vertical coordinates increase downward here is:
consider that when type on computer, increasing lines ==>

unit of measurement is

line of text ~~12 pixels depth -- but skip 15 from one line to next for inter-line space
order of statements appears not to matter much here
but we'll be seeing that things drawn later are drawn on top