Download Java Programming Workshop - Allan Callaghan

Advanced Computing Workshop
Java Programming
Java Programming Workshop
Table of Contents
Java Programming Workshop ................................................................................................................................ 1
Teacher Notes ......................................................................................................................................................... 2
How To ................................................................................................................................................................... 3
Install Java .......................................................................................................................................................... 3
Compiling and running a program ..................................................................................................................... 5
Package a JAR file.............................................................................................................................................. 7
Stage 1: Simple Games ........................................................................................................................................... 8
Top Getting Started Tips .................................................................................................................................... 8
Simple Images .................................................................................................................................................... 9
Tron .................................................................................................................................................................. 10
Physics .............................................................................................................................................................. 13
Race .................................................................................................................................................................. 15
Fly the Copter ................................................................................................................................................... 16
Joust .................................................................................................................................................................. 17
Pong .................................................................................................................................................................. 18
Stage 2: Intermediate Tech ................................................................................................................................... 19
Stars with Arrays .............................................................................................................................................. 20
Gravity .............................................................................................................................................................. 23
Introduction to Post Office Server .................................................................................................................... 24
Objects .............................................................................................................................................................. 25
Stage 3: Advanced Game Techniques .................................................................................................................. 26
Other Projects ....................................................................................................................................................... 27
Network Chat System ....................................................................................................................................... 28
Notes ..................................................................................................................................................................... 32
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Advanced Computing Workshop
Java Programming
Teacher Notes
This document is free to use and distribute under Creative Commons
http://creativecommons.org/licenses/by-nc/2.0/uk/
Java is not the best starting language and I want to convert these resources to use Python and PyGame
Future
Multiball - objects
Platform
Post office server and RPG redered
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Advanced Computing Workshop
Java Programming
How To
Install Java
Windows
1.) Download & Install the JDK
http://java.sun.com/javase/downloads/
Download JDK (Java Development Kit)
Run Installer
2.) Setup Path Environment Variable
Find jdk/bin folder (example shown below)
Copy the complete “bin” path “C:\Program Files\Java\jdk1.6.????\bin”
Right click on “My Computer”
Advanced/Environment Variables
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Advanced Computing Workshop
Java Programming
Add “;(your jdk bin location)” to the end of the Path variable
NOTE: You must put the ; in
Ubuntu Linux
1.
2.
3.
4.
Load Synaptic Package Manager
Refresh list
Search for “jdk”
Mark and Install Sun JDK 6 or higher or
OpenJDK 6 or higher
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Advanced Computing Workshop
Java Programming
Compiling and running a program
Windows XP
Ubuntu Linux
GEdit
Use the commands
Use the commands
LS
Create
program in
text editor
and save it
in your
Java Code
folder
Load a
Command
Prompt
Locate the
folder with
your java
code
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Advanced Computing Workshop
DIR
CD (folder name)
CD ..
Compile
and Run
Use the Commands
javac *.java
java (filename)
[if this is the first time you are running this you will
need to compile the GameLib librarys by typing
compile_gamelib.bat]
Tips
Java Programming
CD (folder name)
CD ..
Use the Commands
javac *.java
java (filename)
[if this is the first time …
in linux you may need to make the file
executable by typing 2 commands:
chmod 755 copile_gamelib.bat
./compile_gamelib.bat
]
Use TAB to auto complete Filenames and Folder
names
Use the UP and DOWN arrows to quickly get
previous commands
Notepad as editor
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Advanced Computing Workshop
Java Programming
Package a JAR file
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Advanced Computing Workshop
Java Programming
Stage 1: Simple Games
Programming Techniques
 Command Line (ls,dir,cd)
 Compilation
 Integer
 Double
 Subroutines
 IF
 String Concatenation
Game Techniques
 Colour Comparison
 Title Screen
 Physics
 Scrolling Background
Top Getting Started Tips
case sensitive
{ paired with }
Indentation
Debug a program: System.out.println(“message”+variable)
// comments
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Advanced Computing Workshop
Java Programming
Simple Images
Putting an image on the screen
import GameLib.GameFrame;
public class ????? extends GameFrame {
public void mousePressed(int x, int y) {
putImage(x,y,"ship.gif");
repaintScreen();
}
public static void main(String[] args) {new ????();}
}
public class ????? extends GameFrame {
public void mouseDragged(int x, int y) {
putImage(x,y,"ship.gif");
repaintScreen();
}
public static void main(String[] args) {new ????();}
}
This leaves a trail of images. We want to drag our space ship around without this trail
public void mouseDragged(int x, int y) {
clearScreen();
putImage(x,y,"ship.gif");
repaintScreen();
}
Challenge
Using these commands can you place stationary shapes on the screen that the drag able ship can be in front the
ship and some behind the ship?
Replace the x,y,width,height,size with numbers.
import GameLib.GameFrame;
import java.awt.Color;
public class ????? extends GameFrame {
public void mouseDragged(int x, int y) {
clearScreen();
drawRectangle(50,50,100,50,Color.YELLOW);
putImage(x,y,"ship.gif");
drawCircleFilled(200,100,size,Color.RED);
drawString(150,200,“This is AWESOME!”);
…
Add more rectangles and ovals
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Advanced Computing Workshop
Java Programming
Tron
Part 1: Simple Line
A Line that Moves
import GameLib.GameFrame;
import java.awt.Color;
import java.awt.event.KeyEvent;
public class ??? extends GameFrame {
int
int
int
int
player1_x_pos = 50;
player1_y_pos = 50;
player1_x_move = 1;
player1_y_move = 0;
public void timerEvent() {
player1_x_pos = player1_x_pos + player1_x_move;
player1_y_pos = player1_y_pos + player1_y_move;
putPixel(player1_x_pos,player1_y_pos,Color.YELLOW);
repaintScreen();
}
public static void main(String[] args) {new ???();}
}
Keyboard Input
Replace the ? with 0, 1 or -1
public void timerEvent() {
if (isKeyPressed(KeyEvent.VK_LEFT ))
if (isKeyPressed(KeyEvent.VK_RIGHT))
if (isKeyPressed(KeyEvent.VK_UP
))
if (isKeyPressed(KeyEvent.VK_DOWN ))
{player1_x_move=?;
{player1_x_move=?;
{player1_x_move=?;
{player1_x_move=?;
player1_y_move=?;}
player1_y_move=?;}
player1_y_move=?;}
player1_y_move=?;}
Player 2
Can you add a second player?
if
if
if
if
(isKeyPressed(KeyEvent.VK_A
(isKeyPressed(KeyEvent.VK_D
(isKeyPressed(KeyEvent.VK_W
(isKeyPressed(KeyEvent.VK_S
))
))
))
))
{???}
{???}
{???}
{???}
Part 2: Collisions
Get the pixel of where we are about to move to.
If it is not black then we have hit an object so reset the players coordinate
…
public void reset() {
clearScreen();
player1_x_pos = 50;
player1_y_pos = 50;
player1_x_move = 1;
player1_y_move = 0;
}
public static void main(String[] args) {new ???();}
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Advanced Computing Workshop
Java Programming
if (Color.BLACK.equals(getPixel(player1_x_pos,player1_y_pos))) {
putPixel(player1_x_pos,player1_y_pos,Color.YELLOW);
}
else {
reset();
}
Part 3: Extras
Score
int player1_deaths = 0;
…
else {
msgBox("Player1 has crashed: " + player1_deaths);
player1_deaths = player1_deaths + 1;
reset();
}
Background Obstacles
…
public ???() {
reset();
}
public void timerEvent() {
…
public void reset() {
clearScreen();
putImage(0,0,”TronLevel.png”);
player1_x_pos = 50;
player1_y_pos = 50;
Part 4: Challenge Ideas
Wrap around
When you go off one side of the screen you appear the other side.
if (player1_x_pos>=getWidth()-1) {player1_x_pos = 1;
}
if (player1_x_pos<=1
) {player1_x_pos = getWidth()-2;}
3 players
Add new keys (try I,J,K,L)
Boost
Pressing a button will make your line move twice as fast
if (isKeyPressed(KeyEvent.VK_DOWN )) {player1_x_move=0; player1_y_move=1;}
if (isKeyPressed(KeyEvent.VK_SPACE)) {
player1_x_move = player1_x_move*2;
player1_y_move = player1_y_move*2;
}
To limit people using this all the time, give them a limited about of booster fuel.
int player1_boost_fuel = 100;
…
if (isKeyPressed(KeyEvent.VK_SPACE)) {
if (player1_boost_fuel>0) {
player1_boost_fuel = player1_boost_fuel – 1;
player1_x_move = player1_x_move*2;
player1_y_move = player1_y_move*2;
}
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Advanced Computing Workshop
Java Programming
}
…
public void reset() {
player1_boost_fuel = 100;
Maze levels
Maze is a one player game to get to the red exit.
Create a set of level graphics 320 by 240 with a black background.
Maze1.png
Maze2.png
int current_level = 1;
…
if (Color.BLACK.equals(getPixel(player1_x_pos,player1_y_pos))) {
putPixel(player1_x_pos,player1_y_pos,Color.YELLOW);
}
else if (Color.RED.equals(getPixel(player1_x_pos,player1_y_pos))) {
current_level = current_level + 1;
reset();
}
else {
reset();
}
…
public void reset() {
clearScreen();
putImage(0,0,”Maze” + current_level + “.png”);
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Advanced Computing Workshop
Java Programming
Physics
Part 1: Simple Moving Spaceship
Before we Begin
Install Java
Copy needed “GameFrame” files
Know how to compile & run java files (“ls”, “dir”, “cd ???”,“javac *.java”, “java ????”)
Drawing and Moving a Spaceship
import GameLib.GameFrame;
import java.awt.event.KeyEvent;
public class ????? extends GameFrame {
private int ship_x_pos = 60;
private int ship_y_pos = 45;
public void timerEvent() {
if (isKeyPressed(KeyEvent.VK_UP
))
if (isKeyPressed(KeyEvent.VK_DOWN ))
if (isKeyPressed(KeyEvent.VK_LEFT ))
if (isKeyPressed(KeyEvent.VK_RIGHT))
{ship_y_pos
{ship_y_pos
{ship_x_pos
{ship_x_pos
+=-1;}
+= 1;}
+=-1;}
+= 1;}
clearScreen();
putImage(ship_x_pos, ship_y_pos,"ship.gif");
repaintScreen();
}
public static void main(String[] args) {new ????();}
}
The spaceship moved in a very jerky and robotic way. We want some physics to make the ship glide.
Part 2: Slide and Glide
Double Arithmetic
Integer store whole numbers (1,69,-7) we need to store double precision numbers (like 3.1415)
private double ship_x_pos = 60.5763;
private double ship_y_pos = 45;
We can only put images at whole number co-ordinates (like [60,45]). Putting an image at [60.5763,45] will not
work.
putImage((int)ship_x_pos, (int)ship_y_pos,"ship.gif");
We convert the double precision numbers to integers (whole numbers) when we draw the spaceship.
You won’t notice much difference when you run it now, but doubles allow us to do cool stuff.
Keeping track of current speed
private
private
private
private
double
double
double
double
ship_x_pos =
ship_y_pos =
ship_x_speed
ship_y_speed
60.5763;
45;
= 0;
= 0;
…
public void timerEvent() {
if (isKeyPressed(KeyEvent.VK_UP
)) {ship_y_speed +=-0.1;}
if (isKeyPressed(KeyEvent.VK_DOWN )) {ship_y_speed += 0.1;}
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Advanced Computing Workshop
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if (isKeyPressed(KeyEvent.VK_LEFT )) {ship_x_speed +=-0.1;}
if (isKeyPressed(KeyEvent.VK_RIGHT)) {ship_x_speed += 0.1;}
clearScreen();
ship_x_pos = ship_x_pos + ship_x_speed;
ship_y_pos = ship_y_pos + ship_y_speed;
putImage((int)ship_x_pos, (int)ship_y_pos,"ship.gif");
repaintScreen();
}
Drag Factor
The spaceship just keeps moving, we want it to slow down on it’s own
public void timerEvent() {
…
clearScreen();
ship_x_speed = ship_x_speed – (ship_x_speed * 0.01);
ship_y_speed = ship_y_speed – (ship_y_speed * 0.01);
ship_x_pos = ship_x_pos + ship_x_speed;
ship_y_pos = ship_y_pos + ship_y_speed;
Constants
We are typing the same numbers again and again like (-0.1).
Professional programmers create a constant they can change in one place
public class ????? extends GameFrame {
private final double move_speed = 0.10;
private final double drag_factor = 0.01;
…
ship_x_speed = ship_x_speed – (ship_x_speed * drag_factor);
ship_y_speed = ship_y_speed – (ship_y_speed * drag_factor);
…
if (isKeyPressed(KeyEvent.VK_UP
)) {ship_y_speed +=-move_speed;}
if (isKeyPressed(KeyEvent.VK_DOWN )) {ship_y_speed += move_speed;}
if (isKeyPressed(KeyEvent.VK_LEFT )) {ship_x_speed +=-move_speed;}
if (isKeyPressed(KeyEvent.VK_RIGHT)) {ship_x_speed += move_speed;}
Part 3: Gravity & Obstacles
Gravity
If an object is falling under gravity it’s y speed will slowly increase.
…
ship_y_speed = ship_y_speed – (ship_y_speed * 0.01);
ship_y_speed = ship_y_speed + 0.01;
ship_x_pos = ship_x_pos + ship_x_speed;
…
Bouncing Boundaries
…
ship_y_speed = ship_y_speed + 0.01;
if (ship_y_pos > getHeight()) {ship_y_speed = -ship_y_speed;}
ship_x_pos = ship_x_pos + ship_x_speed;
…
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Advanced Computing Workshop
Java Programming
Race
This task relies on completing Physics and Tron examples.
Part 1: Track
Create a track image and each timerEvent draw it as a background.
The graphic should be 320 by 240 in size (example right)
public void timerEvent() {
putImage(0,0,"Track1.png");
//keyboard input will go here
//code to move car will go here
//code to draw car graphics go here
repaintScreen();
}
Use your physics example to create a graphic that has coordinates and a speed.
Part 2: Slow Down on Grass
if (Color.BLACK.equals(getPixel(player1_x_pos,player1_y_pos))) {
//do nothing because we are on the track
}
else { //we are off the track
//if we are going to fast make our max speed very slow
if (player1_xspeed> 0.05) {player1_xspeed=0.05;}
if (player1_yspeed> 0.05) {player1_yspeed=0.05;}
if (player1_xspeed<-0.05) {player1_xspeed=-0.05;}
if (player1_yspeed<-0.05) {player1_yspeed=-0.05;}
}
Challenge
Create 2 players.
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Advanced Computing Workshop
Java Programming
Fly the Copter
Create a new image 2000 by 240 with one colour as the background.
Create a cave to fly in like the example and save it as PNG
Part 1: Scrolling background
import GameLib.GameFrame;
public class ????? extends GameFrame {
int background_x_pos = 0;
public void timerEvent() {
background_x_pos = background_x_pos – 1;
if (background_x_pos < -2000) {background_x_pos = 0;}
putImage(background_x_pos,0,"CopterLevel1.png");
repaintScreen();
}
public static void main(String[] args) {new ????();}
}
Part 2: Moving Copter
Simple: Use the physics example.
Make the copter move up and down when you press buttons. (try and use double arithmetic for gravity)
Part 3: Collision detection
Color player_color = getPixel(player1_x_pos,player1_y_pos));
if (Color.BLACK.equals(player_color)) {
}
else if (Color.YELLOW.equals(player_color)) {
current_level = current_level + 1;
reset();
else {
reset();
}
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Advanced Computing Workshop
Java Programming
Joust
Part 1: Title Screen
public Joust() {
titleScreen();
}
public void keyPressed(int key_event) {
if (key_event==KeyEvent.VK_F1
) {reset();}
if (key_event==KeyEvent.VK_EQUALS) {gravity_factor += 0.002; titleScreen();}
if (key_event==KeyEvent.VK_MINUS ) {gravity_factor +=-0.002; titleScreen();}
}
…
public void titleScreen() {
timerPause(true);
clearScreen();
putImage(0,0,"JoustTitle.png");
drawString(100,100,"Player 1: "+player1_score);
drawString(100,120,"Player 2: "+player2_score);
drawString(100,140,"Gravity: " +gravity_factor);
repaintScreen();
}
…
public void startGame() {
//reset player co-ordinates
timerPause(false);
}
Part 2: Collision Detection
Highest wins
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Advanced Computing Workshop
Java Programming
Pong
import GameLib.GameFrame;
import java.awt.Color;
import java.awt.Rectangle;
public class Pong extends GameFrame {
private
private
private
private
Rectangle player1_bat = new Rectangle(20,100,10,40);
Rectangle ball
= new Rectangle(100,100,5,5);
int ball_x_speed = 2;
int ball_y_speed = 2;
public void timerEvent() {
clearScreen();
if (ball.y<0 || ball.y>getHeight()) {ball_y_speed=-ball_y_speed;}
if (ball.x>getWidth())
{ball_x_speed=-ball_x_speed;}
if (player1_bat.contains(ball.x,ball.y)) {ball_x_speed=-ball_x_speed;}
if (ball.x<0) {
msgBox("Missed");
ball.x = 200;
//ball.y = 200;
}
ball.x = ball.x + ball_x_speed;
ball.y = ball.y + ball_y_speed;
drawRectangle(ball,
Color.WHITE);
drawRectangle(player1_bat,Color.WHITE);
repaintScreen();
}
public void mouseMoved(int x, int y) {
player1_bat.x=x;
player1_bat.y=y;
}
public static void main(String[] args) {new Pong();}
}
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Advanced Computing Workshop
Java Programming
Stage 2: Intermediate Tech
Programming Techniques
 Arrays
 Loops
 Collections
o Vector
o Linked List
 Objects
 Multiple Class Files
Game Techniques
Tools
Syntax highlighting
Notepad++
Notepad 2
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Advanced Computing Workshop
Java Programming
Stars with Arrays
One Star
import GameLib.GameFrame;
import java.awt.Color;
public class ??? extends GameFrame {
int star_x =
0;
int star_y = 100;
public void timerEvent() {
clearScreen();
star_x = star_x + 1;
if (star_x > getWidth()) {
star_x = 0;
}
putPixel(star_x, star_y, Color.WHITE);
repaintScreen();
}
public static void main(String[] args) {new ???();}
}
Random Star
import java.awt.Color;
import java.util.Random;
public class ??? extends GameFrame {
int star_x =
0;
int star_y = 100;
private Random random_generator = new Random();
public void timerEvent() {
…
if (star_x > getWidth()) {
star_x = 0;
star_y = random_generator.nextInt(getHeight());
}
…
Two Stars
Modify the program above to have another star.
The thought of typing that all out for 100 stars does not sound fun.
We need a way of storing lots of stars.
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Advanced Computing Workshop
Java Programming
Part 2: Many Many Stars
Star Object
We need to create an object called a star. We need to say what a star has.
public class ??? extends GameFrame {
private SimpleStar my_star
= new SimpleStar();
private Random
random_generator = new Random();
public void timerEvent() {
clearScreen();
my_star.x = my_star.x + 1;
if (my_star.x > getWidth()) {
my_star.x = 0;
my_star.y = random_generator.nextInt(getHeight());
}
putPixel(my_star.x, my_star.y, Color.WHITE);
repaintScreen();
}
public static void main(String[] args) {new ???();}
}
class SimpleStar {
public int x;
public int y;
}
Three Stars
public class ??? extends GameFrame {
private SimpleStar[] stars
= new SimpleStar[3];
private Random
random_generator = new Random();
public ???()
stars[0] =
stars[1] =
stars[2] =
}
{
new SimpleStar();
new SimpleStar();
new SimpleStar();
public void timerEvent() {
clearScreen();
for (SimpleStar star : stars) {
star.x = star.x + 1;
if (star.x > getWidth()) {
star.x = 0;
star.y = random_generator.nextInt(getHeight());
}
putPixel(star.x, star.y, Color.WHITE);
}
repaintScreen();
}
public static void main(String[] args) {new ???();}
}
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Advanced Computing Workshop
Java Programming
Many Many Stars
private SimpleStar[] stars
= new SimpleStar[40];
…
public ???() {
for (int star_number=0 ; star_number<stars.length ; star_number++) {
stars[star_number] = new SimpleStar();
}
}
This isn’t stars!? This is just a line! Why?
Random Start Positions
public ???() {
for (int star_number=0 ; star_number<stars.length ; star_number++) {
SimpleStar s = new SimpleStar();
s.x = random_generator.nextInt(getWidth());
s.y = random_generator.nextInt(getHeight());
stars[star_number] = s;
}
}
Some Stars are faster than others
…
s.y = r.nextInt(getHeight());
s.speed = random_generator.nextInt(number_of_layers) + 1;
stars[star_number] = s;
…
for (SimpleStar star : stars) {
star.x = star.x + star.speed;
…
class SimpleStar {
public int x;
public int y;
public int speed;
}
Challenge
Can you put a spaceship with spaceship physics on top of the stars?
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Advanced Computing Workshop
Java Programming
Gravity
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Advanced Computing Workshop
Java Programming
Introduction to Post Office Server
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Advanced Computing Workshop
Java Programming
Objects
Agents that get extended
Agents have images and an act method (greenfoot inspiration)
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Advanced Computing Workshop
Java Programming
Stage 3: Advanced Game
Techniques
Post office server example
Chat using post office
RPG
Stage
Render stage + moving character
Development enviroments Netbeans
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Advanced Computing Workshop
Java Programming
Other Projects
Network Chat
Calculator
Network AI response
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Advanced Computing Workshop
Java Programming
Network Chat System
Part 1: Setup and Simple Messages
Before we Begin
Install Java
Copy needed “Network Connection” files
Know how to compile java files
Connecting to a server
Create a new .java file based on the code below
import GameLib.Net.AbstractNetworkConnection;
public class ????? extends AbstractNetworkConnection {
public ?????() {
networkConnect("?network address?");
}
public static void main(String[] args) {new ????();}
}
Note: ???? must be the name of the file (CASE SENSETIVE) e.g if your file is called “ChatClient.java” ?????
would be “ChatClient”
Run this code and try to connect to someone’s server. You should see on the servers screen a message that you
connected.
(To find your IP address type “ifconfig” in Linux or “ipconfig” in Windows)
(To run a server type “java GameLib/GameServer show_messages”)
Press Ctrl-C to exit
Sending A “hello” message to the server
public class ?????? extends AbstractNetworkConnection {
public ?????() {
networkConnect("?network address?");
networkSend("Hello everyone! Mr.T has connected");
}
public static void main(String[] args) {new ????();}
}
Adding this line will send a message when you first connect.
BUT! We haven’t written code to SEE messages ….
Receiving messages and displaying them
public void networkReceive(Object message) {
System.out.println(message.toString());
}
public static void main(String[] args) {new ????();}
THINK! Where would you put this code? Look at the indentation.
NOW! With your friends try connecting and disconnecting and try to see each others connect message.
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Advanced Computing Workshop
Java Programming
Part 2: Creating a GUI to type in
Creating a TextField Box
We need a GUI (Graphical User Interface) to type messages into.
We need to IMPORT Java objects to make our interface
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
Put this code at the very beginning of your file
Before you networkConnect setup a Java Frame (JFrame) and Java TextField (JTextField)
private JTextField text_field;
public ?????() {
JFrame frame = new JFrame("Martins Mega Chat Client");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
text_field = new JTextField();
frame.add(text_field,BorderLayout.SOUTH);
frame.pack();
frame.setVisible(true);
networkConnect("?network address?");
networkSend("Hello everyone! Mr.T has connected");
}
You should see a box pop up! Good work!
But it doesn’t work. Why?
Creating a Listener for our JTextField
public class ChatClient extends AbstractNetworkConnection implements ActionListener {
…
text_field = new JTextField();
text_field.addActionListener(this);
frame.add(text_field,BorderLayout.SOUTH);
…
public void actionPerformed(ActionEvent event) {
networkSend(text_field.getText());
}
Use the code to make the JTextField send a message when you press enter.
BUT! What is wrong? (It doesn’t work like we want, why?)
Resetting the JTextField
Can you fix the bug but using the Java API (Application Programming Interface)
Google for “Java API”
Find the documentation for JTextField
Find the command to use, remember you want to “set the text in the box to nothing”
public void actionPerformed(ActionEvent event) {
networkSend( text_field.getText() );
text_field.set????("");
}
Allan Callaghan (http://calaldees.dreamhosters.com/)
Page 29 of 32
Advanced Computing Workshop
Java Programming
Part 3: Creating a GUI to view received messages
Creating a JTextArea box
private JTextField text_field;
private JTextArea text_area;
public ?????() {
JFrame frame = new JFrame("Martins Mega Chat Client");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
text_field = new JTextField();
frame.add(text_field,BorderLayout.SOUTH);
text_area = new JTextArea();
frame.add(text_area,BorderLayout.CENTER);
frame.pack();
…
Run it and resize your chat window and check your JTextArea is there (it will be plain white)
Receiving messages to the JTextArea
public void networkReceive(Object message) {
text_area.append(message.toString() + "\n");
}
Check your program receives messages
BUT! What is wrong? (It doesn’t work like we want, why?)
Scrolling the JTextArea
…
text_area = new JTextArea();
JScrollPane scroll = new JScrollPane(text_area,
JScrollPane.VERTICAL_SCROLLBAR_ALWAYS,
JScrollPane.HORIZONTAL_SCROLLBAR_NEVER);
frame.add(scroll,BorderLayout.CENTER);
frame.pack();
…
Final Bugs
There are a few more bugs to squash (use the “reference”/”useful code” section below)
1. We can type over the received messages area
2. We want lines to wrap to the next line if they are too long
3. When a message is received we always want it scrolled to the bottom
Look at the next Reference section. Can you fix the bugs?
Challenges
See the reference section below + teacher for hints
1. Extreme Challenge: can you get it to connect to servers by “java ChatClient 192.168.0.12”
2. Can you make it so it puts your name in front of every message that you type?
3. Ultimate Challenge: can you make it “java ChatClient 192.168.0.12 Ninja” (where Ninja the name it
will print before each line)
4. Think: What could be done to improve this system if it was going to be used for real?
Allan Callaghan (http://calaldees.dreamhosters.com/)
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Advanced Computing Workshop
Java Programming
Reference
Useful code
text_area.setEditable(false);
text_area.setLineWrap(true);
text_field.setText("");
text_area.setCaretPosition(text_area.getDocument().getLength());
Network Connection Methods Reference
Method
networkConnect(String)
networkDisconnect()
networkSend(Object)
networkIsConnected()
public void networkRecieve(String message) {
public void networkConnected() {
public void networkDisconnecting() {
Type
Description
You write it
You write it
You write it
Extreme Challenge Help
…
public ChatClient(String server_address) {
…
networkConnect(?);
}
…
public static void main(String[] args) {
new ChatClient(args[0]);
}
…
Ultimate Challenge Help
private String username;
…
public ChatClient(String server_address, String new_username) {
username = new_username;
…
networkConnect(?);
}
…
networkSend(username + ": " + text_field.getText());
…
public static void main(String[] args) {
new ChatClient(args[0],args[1]);
}
…
Allan Callaghan (http://calaldees.dreamhosters.com/)
Page 31 of 32
Advanced Computing Workshop
Java Programming
Notes
Add Delay
Add Image Size
Add Image Scale
Add Sound + Music
Joystick input
ReFactor into Jar?
Post office client and examples
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Page 32 of 32