CS100A, Lecture 16, 27 October 1998

1

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.

CS100A, Lecture 16, 27 October 1998

2

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 can’t change.

instance of TextField: a string that the user can change

instance of TextArea:2-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.

CS100A, Lecture 16, 27 October 1998

3

(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);

CS100A, Lecture 16, 27 October 1998

4

part of class Window (superclass of Frame)

public class java.awt.Window extendsjava.awt.Container {

//Constructor

public 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 ();

CS100A, Lecture 16, 27 October 1998

5

part of class Container (superclass of Window)

public class java.awt.Container extendsjava.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( );

CS100A, Lecture 16, 27 October 1998

6

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 inputpublic void disable( ); public void enable( );

// repaint this componentpublic void repaint( );

// Change the width and height to w and hpublic void resize(int w, int h);

// Set the background color to cpublic void setBackground(Color c);

// Make sure the component is seen on the screenpublic void show( );

CS100A, Lecture 16, 27 October 1998

7

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.

Basically, 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.

CS100A, Lecture 16, 27 October 1998

8

GridBagLayout and GridBagConstraints

AAAAA

BBBBBBBB

0 1 2 3 4 5 6 7

0

1

2

3

4

CCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCC

A: TextField

B: Button

C: TextArea

A frame with a TextField, a Button, and a TextArea

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);

CS100A, Lecture 16, 27 October 1998

9

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).

CS100A, Lecture 16, 27 October 1998

10

// 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 buttonsString[ ] bs= {"new game", "quit"};

// The layout and constraint variables for this frameGridBagLayout gbl;GridBagConstraints gbc;

final int xw= 100; // Weights for all the componentsfinal int yw= 100; // when they are resized

(class Experiment to be continued)

CS100A, Lecture 16, 27 October 1998

11

// Constructor: a frame with various componentspublic Experiment() {

super("Experiment");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,gbl,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,gbl,gbc,1,3,1,1,xw,yw);

add(new Button(bs[0]),gbl,gbc, 2,0, 1,1, xw,yw);add(new Button(bs[1]),gbl,gbc, 3,0, 1,1, xw,yw);pack( ); move(150,50); show();setResizable(false);}

CS100A, Lecture 16, 27 October 1998

12

// 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)

CS100A, Lecture 16, 27 October 1998

13

// If button was pressed, process it; otherwise, let method// action in the superclass process itpublic boolean action(Event e, Object arg) {

if (arg.equals(buttons[0])) {// Handle press of "New game" and return true

System.out.println("\"new game\" pressed"); return true;}

if (arg.equals(buttons[1])) {// Handle press of "Quit" and return true

System.out.println("\"Quit\" pressed");System.out.println("TextField is: \"" +

textf.getText( ) + "\"");System.out.println("selection is: \"" +

textf.getSelectedText( ) + "\"");return true;

}return super.action(e,arg);}

(class Experiment to be continued)

CS100A, Lecture 16, 27 October 1998

14

// Process press of WINDOW_DESTROY or mouse up// in a CheckersSquarepublic 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)

CS100A, Lecture 16, 27 October 1998

15

public class TrivialApplication {public static void main(String args[]) {

System.out.println( "Hello World!" );Experiment f= new Experiment();

}

// A square of the game Checkerspublic 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 squareint 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 boardpublic CheckersSquare(int c, int r) {

super();col= c; row= r;if ((c+r)%2 == 1) setBackground(color.gray);else setBackground(color.pink);resize(42,42); b= bounds();repaint();}

(to be continued)

CS100A, Lecture 16, 27 October 1998

16

(continuation of CheckersSquare)

// Constructor: An initially empty square that belongs in// column c, row r of the boardpublic CheckersSquare(int c, int r) {

super();col= c; row= r;if ((c+r)%2 == 1) setBackground(color.gray);else setBackground(color.pink);resize(42,42); b= bounds();repaint();}

// Paint square (with its piece, if any), using Graphics gpublic void paint (Graphics g) {

Color save= g.getColor( ); if (fill==RED) g.setColor(Color.red);else g.setColor(Color.black);g.fillOval(b.x+b.width/5, b.y+b.width/5,

b.width/2, b.height/2);g.setColor(save);}

}

(end of class CheckersSquare)

CS100A, Lecture 16, 27 October 1998

17

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);}

CS100A, Lecture 16, 27 October 1998

18

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.

CS100A, Lecture 16, 27 October 1998

19

Class CheckersSquare

Each square of the checkerboard is an instance of CheckersSquare.

Field fill is the piece on this square

Fields row, col contain the square’s 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.

CS100A, Lecture 16, 27 October 1998

20

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; it’s// the only highlighted square

int clickflag = 0;CheckersSquare oldSq;

int colorToPlay; // player (i.e. color) to place nextint 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 gamepublic void newGame( )

CS100A, Lecture 16, 27 October 1998

21

// Move piece from oldSq to newSq and return true. If// move is not possible, do nothing and return false.private boolean validMove(CheckersSquare 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 squareprivate boolean isValidNonjump(CheckersSquare 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 squareprivate boolean isValidjump(CheckersSquare oldSq, CheckersSquare newSq)

// clickflag=1. 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 playerspublic void processClickTwo(CheckersSquare newSq)