Fundamentals stuff

[Juhan Voolaid]

Hi
I am still having lack of fundamental knowladge about java (general), classes and swing. So prepare yourself for stupid questions.
Firstly i just say what i want to do. I want to make a graphical 2D game where are a main character (player), opponent characters (AI) and a map.
I am planning to design this so:

parent class gamePanel extends JPanel{
 //paintComponent()
 //keyEvents
 //threads
}
class playerChar extends gamePanel{
 //player movment
 //player attack
 //other player methods
}
class oponentChar extends gamePanel{
 //opponent movement
 //opponent attack
 //other methods
}
class map extends gamePanel{
 //methods of generating a map
}

don't really know should i use extends gamepanel or implements gamePanel --what is the difference?
Does only the parent class (gamePanel) have a paintComponent() method? For example with what method in map class can i draw something (e.g. bacground color) to the gamePanel?
OK .. don't know what more to ask now. I have so much things that i want asers to.
So pleas give me some advice to my problems ... don't know where to start.

[Craig Wood]

There are a lot of ways of putting things together to make what you want. The fun comes with practice in making things. Here's something to help you get started.

import java.awt.*;
import java.awt.event.*;
import java.awt.font.*;
import java.awt.geom.*;
import java.util.*;
import java.util.List;
import javax.swing.*;
import javax.swing.event.*;
 
public class Game
{
    public static void main(String[] args)
    {
        JFrame f = new JFrame("Game");
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.getContentPane().add(new GameBoard());
        f.setSize(400,400);
        f.setLocation(200,200);
        f.setVisible(true);
    }
}
 
/**
 * This is the playing field. It draws the tokens on itself and 
 * has listeners (for mouse events) to select and move tokens.
 */
class GameBoard extends JPanel
{
    List tokenList;
 
    public GameBoard()
    {
        tokenList = new ArrayList();
        addTokens();
        setBackground(Color.white);
        TokenMover mover = new TokenMover(this, tokenList);
        addMouseListener(mover);
        addMouseMotionListener(mover);
    }
 
    protected void paintComponent(Graphics g)
    {
        super.paintComponent(g);
        Graphics2D g2 = (Graphics2D)g;
        g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
                            RenderingHints.VALUE_ANTIALIAS_ON);
        int width = getWidth();      // in case you
        int height = getHeight();    // need these someday
        Token t;
        for(int i = 0; i < tokenList.size(); i++)
        {
            t = (Token)tokenList.get(i);
            t.draw(g2);
        }
    }
 
    /**
     * Add tokens to tokenList to be painted on the game board
     */
    private void addTokens()
    {
        tokenList.add(new GoodGuy( 100, 100, Color.pink,  "1", Color.blue));
        tokenList.add(new Opponent(350, 50,  Color.green, "2", Color.orange));
        tokenList.add(new Opponent(150, 325, Color.blue,  "3", Color.red));
    }
}
 
/**
 * Allows us to move tokens on game board.
 * Needs access to token list and game board, references 
 * to these are passed in thru the constructor.
 * Registered as the MouseListener and MouseMotionListener for GameBoard.
 * Handles mouse events for game board.
 */
class TokenMover extends MouseInputAdapter
{
    GameBoard board;
    List list;
    Token selectedToken;
    boolean dragging;
    Point offsetP;
 
    public TokenMover(GameBoard gb, List l)
    {
        board = gb;
        list = l;
        offsetP = new Point();
        dragging = false;
    }
 
    public void mousePressed(MouseEvent e)
    {
        Point p = e.getPoint();
        Token t;
        for(int i = 0; i < list.size(); i++)
        {
            t = (Token)list.get(i);
            Rectangle r = t.getBounds();
            if(r.contains(p))
            {
                selectedToken = t;
                dragging = true;
                offsetP.x = p.x - r.x;
                offsetP.y = p.y - r.y;
            }
        }
    }
 
    public void mouseReleased(MouseEvent e)
    {
        dragging = false;
    }
 
    public void mouseDragged(MouseEvent e)
    {
        if(dragging)
        {
            Point p = e.getPoint();
            int dx = p.x - offsetP.x;
            int dy = p.y - offsetP.y;
            selectedToken.move(dx,dy);
            board.repaint();
        }
    }
}
 
/**
 * Super class for GoodGuy and Opponent objects.
 * All subclasses must implement the abstract methods and
 * they have access to the implemented method (getIdLocation).
 */
abstract class Token
{
    abstract void move(int x, int y);       // these empty methods
    abstract void draw(Graphics2D g);       // are like implementing
    abstract Rectangle getBounds();         // an interface
 
    /**
     * Centers id text inside token shape.
     * You cannot do this (have an implemented method) with an interface.
     */
    protected Point getIdLocation(Graphics2D g2, int dx, int dy, int w,
                                  Font font, String id)
    {
        FontRenderContext frc = new FontRenderContext(null, true, false);
        LineMetrics lm = font.getLineMetrics(id, frc);
        float idWidth = (float)font.getStringBounds(id, frc).getWidth();
        int x = (int)(w - idWidth)/2;
        int y = (int)((w - lm.getHeight())/2 - lm.getDescent());
        Point p = new Point(x,y);
        p.translate(dx,dy);
        return p;
    }
}
 
class GoodGuy extends Token
{
    int x, y;
    Color bgColor, fgColor;
    String id;
    Rectangle2D r;
    int w = 40;
    int h = 40;
    Font font;
 
    public GoodGuy(int cx, int cy, Color c1, String s, Color c2)
    {
        x = cx;
        y = cy;
        bgColor = c1;
        id = s;
        fgColor = c2;
        font = new Font("lucida typewriter bold oblique", Font.PLAIN, 18); // in SDK1.3+
        r = new Rectangle2D.Double(x - w/2, y - h/2, w, h);
    }
 
    public void move(int dx, int dy)
    {
        r.setFrame(dx, dy, w, h);  // move the rectangle
        x = dx + w/2;              // update x and y so
        y = dy + h/2;              // id string can keep up...
    }
 
    public void draw(Graphics2D g2)
    {
        g2.setPaint(bgColor);
        g2.fill(r);
        Point p = getIdLocation(g2, x-w/2, y, w, font, id);
        g2.setPaint(fgColor);
        g2.setFont(font);
        g2.drawString(id, p.x, p.y);
    }
 
    public Rectangle getBounds()
    {
        return r.getBounds();
    }
}
 
class Opponent extends Token
{
    int x, y;
    Color bgColor, fgColor;
    String id;
    Ellipse2D e;
    int dia = 40;
    Font font;
 
    public Opponent(int cx, int cy, Color c1, String s, Color c2)
    {
        x = cx;
        y = cy;
        bgColor = c1;
        id = s;
        fgColor = c2;
        font = new Font("lucida bright italic", Font.PLAIN, 18); // in SDK1.3+
        e = new Ellipse2D.Double(x - dia/2, y - dia/2, dia, dia);
    }
 
    /**
     * Extending the abstract class Token creates the contract that
     * we must implement each of its abstract methods (or declare this
     * class to be abstract). We must implement this method.
     */
    public void move(int dx, int dy)
    {
        e.setFrame(dx, dy, dia, dia);
        x = dx + dia/2;
        y = dy + dia/2;
    }
 
    /**
     * Required implementation of abstract method from Token.
     */
    public void draw(Graphics2D g2)
    {
        g2.setPaint(bgColor);
        g2.fill(e);
        Point p = getIdLocation(g2, x-dia/2, y, dia, font, id);
        g2.setPaint(fgColor);
        g2.setFont(font);
        g2.drawString(id, p.x, p.y);
    }
 
    /**
     * Required implementation.
     */
    public Rectangle getBounds()
    {
        return e.getBounds();
    }
}

[ March 12, 2004: Message edited by: Craig Wood ]

[Juhan Voolaid]

Thank you. That example is perfect to give me answers i am looking for.