GVSU CS 162 Lecture-Module #04: More Details about Statements etc. (Chapter 2)

CS 162 Lecture-Module #04:
More Details about Statements etc. (Chapter 2)

(Chapter 2 of our textbook)

actually first note official, thorough documentation for Java is at http://java.sun.com/
or more specifically http://java.sun.com/javase/6/docs/
particularly http://java.sun.com/javase/6/docs/api/ (API)
and http://java.sun.com/javase/6/docs/api/ (syntax)
plus http://java.sun.com/docs/books/tutorial/index.html (tutorials)
(the API is most useful)

primitive output

System.out.println(...);
produces output
not graphical (NOT drawing circles/colors/...)
just text
where?
that name and this primitiveness reflects that this is
very old fashioned

those monitors with keyboards were called "terminals"
screens had only characters

versus more modern output: graphics, dialogs
e.g. could add the following to Picture.java:
import javax.swing.*;
JOptionPane.showMessageDialog(null, "It's a beautiful day!");

anyway, you can apply System.out.println(...); to Strings, ints, doubles, floats, chars, ...

by the way, to have single char in Java use
e.g.

to have material continue on same line in output,
use System.out.print() instead of System.out.println()
e.g. adding to Circle.java:

 .
  .
   .
    private void draw()
    {
        if(isVisible) {

by the way, can include quotation marks inside String using e.g.:
System.out.print();
...
System.out.println();
alternatively rem. " is a single char so could use :
System.out.println();

by contrast with that joining lines, to have more separated lines in output, do this to produce an empty line:

numeric operations

basic arithmetic ones as usual:
+   -   *   /
e.g.  7 + 6 - 4 * 5 / 2
for further mathematical functions, use Math.SOMETHING
e.g.  Math.sqrt(196),  Math.sin(3),  Math.PI
squaring/cubing/exponentiation(x^y) do NOT have any specific operator, in particular NOT "^" (used for something else)
instead use  Math.pow(x,y) e.g.  Math.pow(3,2),  Math.pow(5,6)

|String| operations

you can material with  Strings using  +
e.g. in  labclasses project, in  LabClass.java, in method  printList():
System.out.println("Lab class " + timeAndDay);
when you do this, technically you get another result  String
then you can concatenate further material with that  String
e.g.  System.out.println("Instructor: " + instructor + "   room: " + room);
e.g.  System.out.println("color is \"" + color + '"');
e.g. to enable better viewing of code with some long output:

  System.out.println("Welcome to the Picture Drawing Program, which is a really nice demonstration of graphics and object-oriented programming.");
  System.out.println("Welcome to the Picture Drawing Program, "
        + "which is a really nice demonstration of graphics "
        + "and object-oriented programming.");

.length()

.indexOf(...)
e.g.  color.indexOf('e')
e.g.  color.indexOf('r')
produces number of characters from  String's beginning to the target
different from 'position' if counted characters starting at 1
instead, here, consider counting characters in  String starting at 0

.substring(beginIndex, limitIndex)
produces contents of String beginning at beginIndex and ending just before limitIndex
e.g. if color is "green",
color.substring(2,5) would yield
color.substring(1,3) would yield

if this way of doing output etc. is so old fashioned, do we need to learn any of it?
well actually you use some of these operations to produce dialogs

methods possibly returning values

all the methods we've examined so far make objects do things
e.g.  Circle.moveVertical(...),  Square.makeVisible()
as they change objects' characteristics, such methods called

alternatively,  methods obtain information from objects

such a method
* needs to indicate what kind of thing it returns via return type
String or  int or something, not just  void used by mutators we've seen
* returns a value via
e.g. add to  class Circle:

then in  Picture.draw() could do:
System.out.println("initially, sun's color: " +  );

further examples in  TicketMachine

if, else

arrange for program to do one thing or another depending on a condition
syntax:

    if ( condition )
    {
        statements
    }
    else
    {
        statements
    }

e.g.:

    if ( x < y )
    {
        System.out.println("The winner is " + x);
    }
    else
    {
        System.out.println("The winner is " + y);
    }

syntax for condition:
* compare values using "<", ">", "<=", ">=", "==", "!="
* check boolean variable

examples in programs we've been using