CS100A Lecture 16 27 October 1998

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• CS100A Lecture 16 27 October 1998
• Assignment 7 A Checker-playing program learning
  about GUIs and working with a well-designed and
  well-documented program
• GUI Graphical User Interface
• Project designed to show advantage of
  object-oriented programming. The
• awt (abstract window toolkit)
• contains many classes --and subclasses-- and
  extending some of them is an integral part of
  implementing a GUI.
• This project will NOT require you to write code
  that deals with the GUI the assignment gives you
  only an introduction to the topic. Your
  programming will deal with the code that
  manipulates the checkers represented in a
  two-dimensional array. And a lot of it requires
  only calling already-written methods.

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• Some classes in the abstract window toolkit
• class Frame An instance is a window on the
  screen. It can contain components. You get to
  say where the components go.
• Frame is a subclass of Window
• Window is a subclass of Container
• Container is a subclass of Component
• Some components that can appear in a Frame
• instance of Button a button to be clicked with
  mouse.
• instance of Label a String that the user cant
  change.
• instance of TextField a string that the user can
  change
• instance of TextArea2-dimensional text area,
  changeable
• instance of Canvas Can be drawn on using
  Graphics
• class Event An instance describes some event,
  like mouse up, mouse drag, click on a
  button, click on the window-destroy field, a
  keystroke.

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(part of) class Frame public class
java.awt.Frame extends java.awt.Window
implements java.awt.MenuContainer
// possible cursor types for method setCursor
public final static int CROSSHAIR_CURSOR
public final static int DEFAULT_CURSOR
public final static int HAND_CURSOR
... public Frame(String title) public void
dispose() public String getTitle()
public void setTitle(String title)
public boolean isResizable() public void
setResizable(boolean resizable) public
int getCursorType() public void
setCursor(int cursorType)
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part of class Window (superclass of
Frame) public class java.awt.Window
extends java.awt.Container //Constructor publi
c Window(Frame parent) // Remove, get rid of,
this window public void dispose ( ) // Lay out
the components in window with preferred
size public void pack( ) // Make this window
visible public void show( ) // Put window
behind other windows public void toBack( ) //
Put window in front of other windows public void
toFront ()
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part of class Container (superclass of
Window) public class java.awt.Container
extends java.awt.Component // Add component
comp to the container public Component
add(Component comp) // remove comp from the
container public void remove(Component comp) //
Tell container what layout manager to use public
void setLayout(LayoutManager mgr) // Lay out
the components in container with // preferred
size public void pack( )
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part of class Component (superclass of
Component) public class java.awt.Component //
Process action, return action has been
handled public boolean action(Event evt, Object
what) // Handle event, return event has been
handled public boolean handleEvent(Event evt)
// Make component insensitive (sensitive) to
use input public void disable( ) public void
enable( ) // repaint this component public void
repaint( ) // Change the width and height to w
and h public void resize(int w, int h) // Set
the background color to c public void
setBackground(Color c) // Make sure the
component is seen on the screen public void show(
)
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Layout Manager Used to place and control
components on a Frame. Several layout managers
--simple ones give programmer less control, the
more complex ones give more There are also
programs that help you build GUIs without having
to do all the programming. Look briefly at one
layout manager, GridBagLayout. Requires an
instance of another class, GridBagConstraints. Ba
sically, to add a new component to the Frame, you
set the properties you want it to have in the
instance of GridBagConstraints and then call a
method add.
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GridBagLayout and GridBagConstraints

gbl new GridBagLayout() gbc new
GridBagConstraints() setLayout(gbl) TextField
tf new TextField(a text field) TextArea ta
new TextArea(text\narea) Button b new
Button(name on button) add(tf,gbl,gbc, 0,0,
3,1, 100,100) add(ta,gbl,gbc, 1,1, 2,2,
100,100) add(tf,gbl,gbc, 3,2, 5,3,
100,100)
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Following slides class Experiment, which is an
extension of Frame. It has several components in
the frame. class TrivialApplication, which
defines a variable that can contain an
Experiment. class CheckersSquare (stripped down
version), a component of class Canvas. We spend
some time demonstrating and investigating these
classes. You can download these three classes in
a single file from our web site (look for
assignment 7). Start a new codewarrior project,
using the Java application stationery (not the
CUCS stationery). Then replace file
TrivialApplication.java with this file (of the
same name).
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// Frame to illustrate the awt. public class
Experiment extends Frame // Components that go
in the frame CheckersSquare sq Label lab
TextField textf TextArea texta // Titles for
buttons String bs "new game", "quit" //
The layout and constraint variables for this
frame GridBagLayout gbl GridBagConstraints
gbc final int xw 100 // Weights for all the
components final int yw 100 // when they are
resized (class Experiment to be continued)
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// Constructor a frame with various
components public Experiment() super("Experimen
t") gbl new GridBagLayout() gbc new
GridBagConstraints() setFont(new Font("Dialog",
Font.PLAIN, 10)) setLayout(gbl) gbc.fill
gbc.BOTH sq new CheckersSquare(0,0) add(sq,gb
l,gbc,0,0,1,1,xwt,yw) gbc.fill
gbc.BOTH lab new Label("A label at
(1,1)") add(lab, gbl,gbc,1,1,1,1,xw,yw)
textf new TextField("A TextField at (1,2)")
add(textf,gbl,gbc,1,2,1,1,xw,yw) texta
new TextArea("A TextArea\nat (1,3)") add(texta,g
bl,gbc,1,3,1,1,xw,yw) add(new
Button(bs0),gbl,gbc, 2,0, 1,1, xw,yw) add(new
Button(bs1),gbl,gbc, 3,0, 1,1, xw,yw) pack(
) move(150,50) show() setResizable(false)

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// Add component c to gbl with constraints gbc at
position // (x,y). Component c takes w columns
and r rows, and is // weighted (wx, wy). private
void add(Component c, GridBagLayout
gbl, GridBagConstraints gbc, int x, int
y, int w, int h, int wx, int wy) gbc.gridx
x gbc.gridy y gbc.gridwidth
w gbc.gridheight h gbc.weightx
wx gbc.weighty wy gbl.setConstraints(c,
gbc) add(c) (class Experiment to be
continued)
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// If button was pressed, process it otherwise,
let method // action in the superclass process
it public boolean action(Event e, Object arg)
if (arg.equals(buttons0)) // Handle
press of "New game" and return true System.out.
println("\"new game\" pressed") return
true if (arg.equals(buttons1)) // Handle
press of "Quit" and return true System.out.prin
tln("\"Quit\" pressed") System.out.println("Te
xtField is \"" textf.getText( )
"\"") System.out.println("selection is \""
textf.getSelectedText( )
"\"") return true return
super.action(e,arg) (class Experiment to be
continued)
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// Process press of WINDOW_DESTROY or mouse up //
in a CheckersSquare public boolean
handleEvent(Event e) //System.out.println(""
e) if (e.id Event.WINDOW_DESTROY)
System.out.println("Window destroy
clicked") //dispose() return true if
(e.id Event.MOUSE_UP e.target instanceof
CheckersSquare) System.out.println("Mouse up
in a CheckersSquare") return
true if (e.id Event.MOUSE_MOVE)
System.out.println("Mouse move") return
true return super.handleEvent(e) (
End of class Experiment)
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public class TrivialApplication public static
void main(String args) System.out.println(
"Hello World!" ) Experiment f new
Experiment() // A square of the game
Checkers public class CheckersSquare extends
Canvas static public final int EMPTY 0 static
public final int RED 1 static public final int
BLACK 2 Rectangle b // Containing
rectangle of this square int col int row// col,
row no. of this square on board private int
fill EMPTY // Constructor An initially empty
square that belongs in // column c, row r of the
board public CheckersSquare(int c, int r)
super() col c row r if ((cr)2 1)
setBackground(color.gray) else
setBackground(color.pink) resize(42,42) b
bounds() repaint() (to be continued)
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(continuation of CheckersSquare) // Constructor
An initially empty square that belongs in //
column c, row r of the board public
CheckersSquare(int c, int r) super() col c
row r if ((cr)2 1) setBackground(color.gra
y) else setBackground(color.pink) resize(42,42
) b bounds() repaint() // Paint square
(with its piece, if any), using Graphics g public
void paint (Graphics g) Color save
g.getColor( ) if (fillRED)
g.setColor(Color.red) else
g.setColor(Color.black) g.fillOval(b.xb.width/5
, b.yb.width/5, b.width/2,
b.height/2) g.setColor(save) (end of
class CheckersSquare)
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EVENTS Event something like mouse down, mouse
drag, click on a button, pressing a key down,
letting a key up, and clicking on the
window-destroy box. An event represented by an
instance of class Event. Java 1.0 event handling
is different from Java 1.1 event handling. We
discuss Java 1.0 event handling. When an event
happens, one of two methods is called // Handle
button click --return click processed public
boolean action(Event e, Object arg) Similar to
body of handleEvent // Handle all other events
--return event handled public boolean
handleEvent(Event e) if (event can be handled)
Process event return true return
super.handleEvent(e)
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The game of checkers To play the game using a
finished program, execute the applet on the
CS100A home page (look for assignment 7). For
this assignment, download files as instructed on
the handout for the assignment. You get a copy of
the completed program with parts removed, and you
have to fill them in. You will not have to write
code that manipulates the GUI, but you are
encouraged to study the GUI code! Class Checkers
is a subclass of Frame, so an instance is a
window on the monitor. Class CheckersSquare is a
subclass of Canvas, so an instance is a component
on which one can draw ovals and such. An 8x8
array of elements of Class CheckersSquare forms
the checker board. Class IntLabel is used to
encode two different representations of a number
Int and Label.
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Class CheckersSquare Each square of the
checkerboard is an instance of CheckersSquare. Fi
eld fill is the piece on this square Fields row,
col contain the squares row, col number Field
toBeMoved The piece should be
highlighted Method paint is called by the
system whenever the square should be repainted.
Repainging can also be requested by a method of
this class by calling method repaint. Class
CheckersSquare contains a bunch of methods that
you should use in writing your code. Spend
several minutes familiarizing yourself with them
before doing any coding.
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Class Checkers Fields for checker game (not
GUI) // Number of red pieces and black pieces on
the board IntLabel redCount new IntLabel(0,
reds) IntLabel blackCount new IntLabel(0,
blacks) // clickflag describes clicks made by
the user // 0 No piece has been chosen
(clicked on). For all // squares, field
toBeMoved is false. // 1 click was made on
a piece of color colorToPlay // oldSq is
the square of the piece to be moved its // the
only highlighted square int clickflag
0 CheckersSquare oldSq int colorToPlay //
player (i.e. color) to place next int
otherColor // the other color Your changes are
restricted to five methods, but before you make
the changes, study carefully at all the other
methods in class Checkers. // Set the board up
for a new game public void newGame( )
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// Move piece from oldSq to newSq and return
true. If // move is not possible, do nothing and
return false. private boolean validMove(CheckersSq
uare oldSq, CheckersSquare newSq) // Return
"move oldSq to newSq is valid non-jump // move
for player colorToPlay". Assume oldSq contains //
a piece of colorToPlay and newSq is empty black
square private boolean isValidNonjump(CheckersSqua
re oldSq, CheckersSquare newSq) // Return
"move oldSq to newSq is valid jump for player //
colorToPlay". Assume oldSq contains piece and
that // newSq is an empty black square private
boolean isValidjump(CheckersSquare oldSq,
CheckersSquare newSq) // clickflag1. If
pieces on oldSq and newSq have same // color,
switch to moving the piece on newSq. Otherwise //
try to move piece from oldSq to square newSq. If
not // possible, give error message if possible,
do it and // switch players public void
processClickTwo(CheckersSquare newSq)