Develop Reference

How to use a timer to repaint some swing components

INTRODUCTION
Hi guys, I was learning how to make a little game where you are a racquet (rectangle) and all the asteroids (enemies) are falling down the screen and you have to avoid them
PROBLEM
When the game starts the enemies (asteroids) are paint on the screen in a very high speed, and they occupy all the size of the screen so there is no way to avoid them (try the game), I just want that between painting an enemy and the next one there is a mininum time to delay (for example 0,5 seconds).
But I just don't know how to do that, I tried to use Thread.sleep() and TimeUnit but they just make the game slower.
Surfing on stackoverflow I've find out that I may try to use Swing timers, I've read some stuff on the web but I want to know how can I use swing timers in my code (if they can solve my problem).
Here it is the code:
The main class:
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.RenderingHints;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import java.util.ArrayList;
import java.util.Random;
import java.util.concurrent.TimeUnit;
import javax.swing.JFrame;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.Timer;
#SuppressWarnings("serial")
public class Game extends JPanel {
Racquet racquet = new Racquet(this);
Enemy Enemy = new Enemy(this);
static ArrayList<Enemy> enemyList = new ArrayList<Enemy>();
public Game() {
addKeyListener(new KeyListener() {
#Override
public void keyTyped(KeyEvent e) {
}
#Override
public void keyReleased(KeyEvent e) {
racquet.keyReleased(e);
}
#Override
public void keyPressed(KeyEvent e) {
racquet.keyPressed(e);
}
});
setFocusable(true);
}
/** TO SET THE RANDOM POSITION ON WHERE THE ENEMIES HAVE TO APPEAR ON THE SCREEN **/
public int random(int x, int y, ArrayList<Enemy> pa){
int r = 0;
for(int i = 0; i<pa.size(); i++){
Random rand = new Random();
r = rand.nextInt(x+y)-1;
return r;
}
return r;
}
/** letting the enemies move on the screen **/
private void move() {
for(int i = 0; i < enemyList.size(); i++){
enemyList.get(i).move();
}
racquet.move();
}
/** Painting on the screen enemies and the racquet **/
#Override
public void paint(Graphics g) {
super.paint(g);
Graphics2D g2d = (Graphics2D) g;
g2d.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
for(int i = 0; i < enemyList.size(); i++){
enemyList.get(i).paint(g2d);
}
racquet.paint(g2d);
}
public void gameOver() {
JOptionPane.showMessageDialog(this, "Game Over", "Game Over", JOptionPane.YES_NO_OPTION);
System.exit(ABORT);
}
public void createEnemy(){
enemyList.add(new Enemy(this));
}
public static void main(String[] args) throws InterruptedException {
JFrame frame = new JFrame("Asteroids");
Game game = new Game();
frame.add(game);
frame.setSize(300, 400);
frame.setVisible(true);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
game.random(200, 300, enemyList);
while (true) {
game.createEnemy();
game.move();
game.repaint();
Thread.sleep(5);
}
}
}
The racquet class:
import java.awt.Graphics2D;
import java.awt.Rectangle;
import java.awt.event.KeyEvent;
public class Racquet {
private static final int Y = 330;
private static final int WIDTH = 30;
private static final int HEIGHT = 6 ;
int x = 0;
int xa = 0;
private Game game;
public Racquet(Game game) {
this.game = game;
}
/** letting the racquet moves on the screen **/
public void move() {
if (x + xa > 0 && x + xa < game.getWidth() - WIDTH)
x = x + xa;
}
/** Creating the rectangle racquet **/
public void paint(Graphics2D g) {
g.fillRect(x, Y, WIDTH, HEIGHT);
}
/** // Setting xa everytime to 0, if we don't do this it just takes a single pression to go to a direction until we press the other key **/
public void keyReleased(KeyEvent e) {
xa = 0;
}
/** Choosing the direction **/
public void keyPressed(KeyEvent e) {
if (e.getKeyCode() == KeyEvent.VK_LEFT)
xa = -1;
if (e.getKeyCode() == KeyEvent.VK_RIGHT)
xa = 1;
}
public Rectangle getBounds() {
return new Rectangle(x, Y, WIDTH, HEIGHT);
}
public int getTopY() {
return Y;
}
}
And the enemy class:
import java.awt.Graphics2D;
import java.awt.Rectangle;
import java.util.*;
public class Enemy {
private Game game;
int x = 0;
int y = 0;
int xa = 1;
int ya = 1;
/** Generating a random position where the enemies have to appear **/
public Enemy(Game game){
this.game = game;
x = game.random(0, 320, game.enemyList);
}
/** Paint the enemies **/
public void paint(Graphics2D g) {
g.fillRect(x, y, 20, 20);
}
/** move the enemies and detect collisions **/
public void move(){
y += ya;
if(collision()){
game.gameOver();
}
}
/** returns true if the enemy rectangle touch the racquet **/
public boolean collision(){
return game.racquet.getBounds().intersects(getBounds());
}
public Rectangle getBounds() {
return new Rectangle(x, y, 20, 20);
}
}

Suggestions:
Your game "tick" time is 5 mSecs, a not quite reasonable time. I suggest that
You get rid of the "magic" number, using a constant instead,
and make the tic a little bigger, say 12 to 15 mSec.
Also better to use a Swing Timer or to at least make sure that you do your while loop in a defined background thread.
Most importantly, you're creating a new enemy with each tick of your game loop, and that's too fast. Instead:
Don't create a new Enemy with each tick,
Instead save the time that the last enemy was created in a field,
Check the delta-time, the current system time - lastEnemyCreationTime, inside of your game-loop,
Only create a new enemy if the delta-time is greater than a reasonable value, either a constant value or a field (not a magic number).
On creation of the new enemy, reset the lastEnemyCreationTime to the current system time.
Unrelated recs:
Override the JPanel's paintComponent, not the paint method as this will give you double buffering by default which can lead to smoother perceived graphics.
Favor using Key Bindings over a KeyListener as this will help to easily eliminate focus issues inherent with use of KeyListeners.

Image flickering when call paint() method

package Game;
import java.awt.*;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import javax.swing.*;
import Maps.*;
public class Window extends JFrame implements KeyListener
{
private Insets insets;
private int currentMapX;
private int currentMapY;
public Window()
{
super();
setSize(new Dimension(1920, 1080));
setLayout(null);
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
setUndecorated(true);
setFocusable(true);
setContentPane(new Container());
setBackground(Color.BLACK);
addKeyListener(this);
}
public void startGame()
{
insets = getInsets();
currentMapX = 960 - (Game.level_01.getWidth() / 2);
currentMapY = 540 - (Game.level_01.getHeight() / 2);
Game.level_01.setBounds(currentMapX, currentMapY, Game.level_01.getWidth(), Game.level_01.getHeight());
add(Game.level_01);
}
private void moveMapRight()
{
Game.level_01.setBounds(++currentMapX, currentMapY, Game.level_01.getWidth(), Game.level_01.getHeight());
}
private void moveMapLeft()
{
Game.level_01.setBounds(--currentMapX, currentMapY, Game.level_01.getWidth(), Game.level_01.getHeight());
}
public void paint(Graphics g)
{
super.paint(g);
Graphics2D g2d = (Graphics2D)g;
g2d.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
Game.player.paint(g2d);
}
public void keyPressed(KeyEvent k)
{
if(k.getKeyCode() == KeyEvent.VK_RIGHT) moveMapRight();
if(k.getKeyCode() == KeyEvent.VK_LEFT) moveMapLeft();
}
public void keyReleased(KeyEvent k){}
public void keyTyped(KeyEvent k){}
}
I've got the first class that extends the JFrame and contains the following class.
package Maps;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Insets;
import java.awt.RenderingHints;
import java.io.*;
import java.util.*;
import javax.swing.*;
import Game.*;
import Tiles.*;
public class Level extends JPanel
{
protected final File txt_MAP;
protected final ArrayList<Tile> jLabel_MAP;
protected final ArrayList<Integer> linesLength;
protected Insets insets = Game.window.getInsets();
protected int arrayIndex;
protected int leftIndex;
protected int topIndex;
protected int width;
protected int height;
public Level(File f)
{
super();
setLayout(null);
setBackground(Color.BLACK);
leftIndex = 0;
topIndex = 0;
txt_MAP = f;
jLabel_MAP = new ArrayList<>();
linesLength = new ArrayList<>();
arrayIndex = 0;
readTxt();
width = linesLength.get(0) * Game.tileSize;
height = linesLength.size() * Game.tileSize;
addTiles();
}
private void readTxt()
{
BufferedReader br = null;
try
{
br = new BufferedReader(new FileReader(txt_MAP));
}
catch(FileNotFoundException e){}
try
{
String line = br.readLine();
while(line != null)
{
String[] words = line.split(" ");
for(int a = 0; a < words.length; a++)
{
for(int b = 0; b < Game.tilesIcons.length; b++)
{
if(Game.tilesList[b].getName().equals(words[a] + ".gif"))
{
if(Game.tilesList[b].getName().contains(Game.grass_TYPE)) jLabel_MAP.add(arrayIndex, new Grass(Game.tilesIcons[b]));
if(Game.tilesList[b].getName().contains(Game.soil_TYPE)) jLabel_MAP.add(arrayIndex, new Soil(Game.tilesIcons[b]));
if(Game.tilesList[b].getName().contains(Game.sky_TYPE)) jLabel_MAP.add(arrayIndex, new Sky(Game.tilesIcons[b]));
arrayIndex++;
}
}
}
linesLength.add(words.length);
line = br.readLine();
}
}
catch(IOException e){}
}
private void addTiles()
{
for(int i = 0; i < jLabel_MAP.size(); i++)
{
jLabel_MAP.get(i).setBorder(null);
jLabel_MAP.get(i).setBounds(insets.left + leftIndex, insets.top + topIndex, 64, 64);
add(jLabel_MAP.get(i));
if(leftIndex == width - Game.tileSize)
{
leftIndex = 0;
topIndex += 64;
}
else leftIndex += 64;
}
}
public int getWidth()
{
return width;
}
public int getHeight()
{
return height;
}
}
This class extends JPanel and contains an arrayList of Jlabels.
package Player;
import java.awt.*;
import Game.*;
public class Player
{
private int x;
private int y;
private int xa;
private int ya;
private Graphics2D g2d;
public Player(double x, double y)
{
super();
this.x = (int)x;
this.y = (int)y;
xa = 0;
ya = 1;
}
public void movePlayer()
{
x += xa;
y += ya;
}
public void setDirection(int xa, int ya)
{
this.xa = xa;
this.ya = ya;
}
public void paint(Graphics g)
{
g2d = (Graphics2D)g;
g2d.drawImage(Game.playerImages[6], x , y, Game.tileSize, Game.tileSize, null);
}
public int getX()
{
return x;
}
public int getY()
{
return y;
}
public int getXA()
{
return xa;
}
public int getYA()
{
return ya;
}
}
Finally this class is the class for the player, that is a BufferedImage. My problem is that when I start the program, the player image starts flickering, because when I call the paint() method in the JFrame class, this paints the first the jpanel and then the player image. How can I solve the Image flickering?
Thanks in advance.

As others have said, you shouldn't override paint(Graphics g) in top-level components, so that's part of the problem, but you also need to be careful to make sure you only paint to the screen once per repaint:
My problem is that when I start the program, the player image starts
flickering, because when I call the paint() method in the JFrame
class, this paints the first the jpanel and then the player image.
What's happening now is, every time you call a method that modifies the Graphics object in your paint(Graphics screen) method, it's directly modifying the screen contents, forcing the screen to refresh before you've finished drawing what you really wanted to - the Player. By first painting to super, then again with your custom rendering, you're actually painting to screen at least twice, causing the flicker. You can fix this by double buffering.
Double Buffering involves first rendering to an image, then painting that image to screen. Using built-in methods provided by the Component class (remember that JPanel extends Component), you can get the size of the viewable area of your component. Create a BufferedImage of the same size, then call bufferedImage.createGraphics() - this will give you a Graphics2D object that you can use to draw onto your bufferedImage with. Once you're done rendering to bufferedImage, call screen.drawImage(bufferedImage,0,0,null). This allows you to modify the bufferedImage as many times as you want without actually doing a screen refresh, then draw the contents of the buffer to screen in a single call.
ADDITIONAL INFO
I should have pointed out earlier that I know nothing about how things are actually laid out on screen for you, so you may need to do some additional checks on the bounds of your Player's screen area and where the upper left should be placed in the call to drawImage(Image,x,y,ImageObserver). Also be aware of transparency or the lack thereof in your BufferedImage - you can easily get lost if you paint opaque pixels over other important stuff on screen.
TRY THIS (but don't keep it)
Again, I don't recommend doing all of your painting in top-level components, but you could try doing something like this in the interim:
//This is in the Window class:
public void paint(Graphics screen)
{
//Render everything first to a BufferedImage:
BufferedImage bufferedImage = ... //Initialize based on Window's
//size and bounds.
Graphics2D buf = bufferedImage.createGraphics();
super.paint(buf);
buf.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
RenderingHints.VALUE_ANTIALIAS_ON);
Game.player.paint(buf);
//Now paint the buffer to screen:
int x = ... //set to top-left x-coordinate, probably 0
int y = ... //set to top-left y-coordinate, probably 0
screen.drawImage(buf,x,y,null);
}

Don't override paint(Graphics) in a top level container like JFrame (which is not double buffered). Instead do custom painting in a JPanel (which is double buffered).
Also, when overriding any of the paint methods, immediately call the super method thereby painting the background and effectively erasing the earlier drawing(s).

Breakout ball collision in libgdx

I'm currently trying to make a breakout clone using java and libgdx. I'm currently experiencing trouble getting the ball to bounce off of the blocks at the appropriate angle. In short the problem I'm having is that the ball moves 12 pixels every frame and doesn't always line up with the edge of a brick. If anyone has any suggestions on a better way to move the ball or a different way to check collision it would be much appreciated!
Main game class
package com.kyleparker.breakout;
import com.badlogic.gdx.ApplicationListener;
import com.badlogic.gdx.Gdx;
import com.badlogic.gdx.audio.Music;
import com.badlogic.gdx.audio.Sound;
import com.badlogic.gdx.graphics.GL10;
import com.badlogic.gdx.graphics.OrthographicCamera;
import com.badlogic.gdx.graphics.Texture;
import com.badlogic.gdx.graphics.g2d.SpriteBatch;
import com.badlogic.gdx.math.Rectangle;
import com.badlogic.gdx.utils.Array;
public class BreakoutGameScreen implements ApplicationListener {
Texture dropImage;
Sound dropSound;
Music rainMusic;
SpriteBatch batch;
OrthographicCamera camera;
Rectangle bucket;
Paddle paddle;
//Brick bricks[];
Array<Brick> bricks;
Ball ball;
#Override
public void create() {
// load the images for the droplet, 64x64 pixels
dropImage = new Texture(Gdx.files.internal("droplet.png"));
// load the drop sound effect and the rain background "music"
dropSound = Gdx.audio.newSound(Gdx.files.internal("drop.wav"));
rainMusic = Gdx.audio.newMusic(Gdx.files.internal("rain.mp3"));
// start the playback of the background music immediately
rainMusic.setLooping(true);
rainMusic.play();
// create the camera and the SpriteBatch
camera = new OrthographicCamera();
camera.setToOrtho(false, 1280, 720);
batch = new SpriteBatch();
paddle = new Paddle(new Texture(Gdx.files.internal("bucket.png")));
bricks = new Array<Brick>();
populateBricks();
ball = new Ball(new Texture(Gdx.files.internal("bucket.png")), paddle, bricks);
}
private void populateBricks() {
bricks.add(new Brick(200,100));
for (int i = 0; i < 5; i++) {
for (int j = 0; j <= 7; j++) {
bricks.add(new Brick (j * 144 + 76, i * 80 + 300)); //Offsets each new brick
}
}
}
#Override
public void render() {
// clear the screen with a dark blue color. The
// arguments to glClearColor are the red, green
// blue and alpha component in the range [0,1]
// of the color to be used to clear the screen.
Gdx.gl.glClearColor(0, 0, 0.2f, 1);
Gdx.gl.glClear(GL10.GL_COLOR_BUFFER_BIT);
// tell the camera to update its matrices.
camera.update();
// tell the SpriteBatch to render in the
// coordinate system specified by the camera.
batch.setProjectionMatrix(camera.combined);
// begin a new batch and draw the bucket and
// all drops
batch.begin();
paddle.render(batch, camera);
ball.move();
ball.render(batch, camera);
for (int x = bricks.size - 1; x > 0; x--) {
bricks.get(x).render(batch,camera);
}
batch.end();
}
#Override
public void dispose() {
// dispose of all the native resources
dropImage.dispose();
dropSound.dispose();
rainMusic.dispose();
batch.dispose();
paddle.dispose();
}
#Override
public void resize(int width, int height) {
}
#Override
public void pause() {
}
#Override
public void resume() {
}
}
Ball class
package com.kyleparker.breakout;
import com.badlogic.gdx.graphics.OrthographicCamera;
import com.badlogic.gdx.graphics.Texture;
import com.badlogic.gdx.graphics.g2d.SpriteBatch;
import com.badlogic.gdx.math.Rectangle;
import com.badlogic.gdx.utils.Array;
public class Ball{
Texture ballImage;
Rectangle ball;
private int xdir;
private int ydir;
Paddle paddle;
Array<Brick> bricks;
final int BALL_SPEED = 12;
public Ball(Texture ballImage, Paddle paddle, Array<Brick> bricks) {
// load the ball image
this.ballImage = ballImage;
xdir = 1;
ydir = -1;
// create a Rectangle for the balls collision
ball = new Rectangle();
ball.x = 1280 / 2 - 64 / 2; // center the ball
ball.y = 100; // put the ball 200px away from the bottom of the screen
ball.width = 64;
ball.height = 64;
this.paddle = paddle;
this.bricks = bricks;
}
public void render(SpriteBatch batch, OrthographicCamera camera) {
// draw the paddle onto the batch of the level
batch.draw(ballImage, ball.x, ball.y);
}
public void move() {
ball.x += xdir * BALL_SPEED;
ball.y += ydir * BALL_SPEED;
if (ball.x <= 0) {
setXDir(1);
}
if (ball.x >= 1280 - 64) {
setXDir(-1);
}
if (ball.y <= 0) {
setYDir(1);
}
if (ball.y >= 720 - 64) {
setYDir(-1);
}
if (ball.overlaps(paddle.getRect())) {
setYDir(1);
}
for (int i = 0; i < bricks.size; i++) {
if (ball.overlaps(bricks.get(i).getRect())) {
if ((ball.x == (bricks.get(i).getRect().x + 128)))
{
setXDir(1);
bricks.get(i).setDestroyed(true);
System.out.println("Collision RIGHT");
}
if (((ball.x + 64) == bricks.get(i).getRect().x))
{
setXDir(-1);
bricks.get(i).setDestroyed(true);
System.out.println("Collision LEFT");
}
if ((ball.y == (bricks.get(i).getRect().y + 64)))
{
setYDir(1);
bricks.get(i).setDestroyed(true);
System.out.println("Collision TOP");
}
if (((ball.y + 64) == bricks.get(i).getRect().y))
{
setYDir(-1);
bricks.get(i).setDestroyed(true);
System.out.println("Collision BOTTOM");
}
}
}// end of for
}
public void setXDir(int x) {
xdir = x;
}
public void setYDir(int y) {
ydir = y;
}
public int getYDir() {
return ydir;
}
public int getXDir() {
return xdir;
}
public Rectangle getRect() {
// return the collision rectangle for checking overlaps
return ball;
}
public void dispose() {
// dispose of all the native resources
ballImage.dispose();
}
}// end of class
Brick code just in case
package com.kyleparker.breakout;
import com.badlogic.gdx.Gdx;
import com.badlogic.gdx.graphics.OrthographicCamera;
import com.badlogic.gdx.graphics.Texture;
import com.badlogic.gdx.graphics.g2d.SpriteBatch;
import com.badlogic.gdx.math.Rectangle;
public class Brick{
Texture brickImage;
Rectangle brick;
boolean destroyed;
public Brick(int x, int y) {
brickImage = new Texture(Gdx.files.internal("brick.png"));
// create a Rectangle for the bricks collision
brick = new Rectangle();
brick.x = x;
brick.y = y;
brick.width = 128;
brick.height = 64;
destroyed = false;
}
public void render(SpriteBatch batch, OrthographicCamera camera) {
// draw the brick onto the batch of the level
batch.draw(brickImage, brick.x, brick.y);
}
public boolean isDestroyed() {
// return the collision rectangle for checking overlaps
return destroyed;
}
public void setDestroyed(boolean destroyed)
{
this.destroyed = destroyed;
if (this.destroyed == true) {
dispose();
brick.x = -1000;
brick.y = -1000;
}
}
public Rectangle getRect() {
return brick;
}
public void dispose() {
// dispose of all the native resources
brickImage.dispose();
}
}

Don't worry about the fact that the ball doesn't always line up with an object for which the collision needs handled -- that's not actually relevant. You can (and should) handle your collisions less 'precisely.' That is, the ball's path is fixed, so you can calculate its position at any future point. Check its position, calculate its position in the next frame (which you have to do to draw it anyway), and add some code to handle the collision that is going to happen, rather than trying to detect and handle the collision which has happened. You can slow down the ball if you really want a clean reflection, or you can speed up your framerate, or you can let the ball be partially 'absorbed' by the object before it reflects:
public class Ball {
. . .
public void move() {
. . .
if (collisionObject.overlaps(new Rectangle(ball.x + xdir, ball.y + ydir, ball.width, ball.height))) {
//a collision will have occurred in the next frame
//handle the collision however you please
}
}
}
I also note that your BALL_SPEED field is inaccurately named. As presently coded, the ball always moves at a 45° angle, with a speed of about 17 pixels per frame (in that direction). You've coded its x- and y-offset as 12 pixels, but if (when?) you change the ball's direction, you'll find that the speed fluctuates wildly depending on what values are placed in for the xdir and ydir fields. For example, if you were to (somewhat) randomize these, but keep the rest of your code as-is, you might find that xdir = 2 and ydir = 4 on one instance, and xdir = 6 and ydir = 12 on another. Note these describe the same direction, but the second version will move three times as fast.
To properly handle the ball's direction and speed, assign an angle, and calculate the xdir and ydir values through the appropriate trigonometric functions (xdir = BALL_SPEED * Math.cos(ballAngle) and ydir = BALL_SPEED * Math.sin(ballAngle)).

I would use box2d for the whole thing. That you haven't used box2d probably means you have no experience in it, so that would be a little hurdle, but I'm sure you'll be able to wrap your head around it quickly. Here's a link for that: http://code.google.com/p/libgdx/wiki/PhysicsBox2D

Simulating rain

I am making a game in java and I want to create a simulation of a cloud that is pouring rain. The cloud is supposed to move to the right while raining. Moving the cloud is no problem. It's the rain that I am struggling with.
What I was thinking of doing was with a timer to draw a rectangle, thats supposed to look like falling rain at a random x value inside of the cloud. And then add 1 to the y value of the drop each 100 millisecond. But I don't want to create 100 different rectangles, x variables and y variables for each rain drop.
Any idea how I can accomplish this? Suggestions appreciated!
It is a 2d game.. Sorry.

One approach would be to consider a marquee on a theater. You take a series of bulbs and, by lighting and extinguishing them in sequence, you can simulate linear motion.
In the same way, rather than creating raindrops and animating their movement, why not creating multiple raindrops that are invisible and show and hide them in sequence to simulate downward motion. Then, you would have a series of arrays representing a raindrop track and you simply need to cycle through then, hiding the current one, incrementing the array pointer and displaying that one.

Is it a requirement that the rain drops be programmed? Traditionally, this would be done with a few rain sprites that you place under the cloud and animate so that it looks like the rain is falling.

I would recommend just storing the values as an ArrayList of objects.
class Raindrop {
private int x;
private int y;
public void fall() {
y--;
}
}
Then make an ArrayList with a generic type.
ArrayList<Raindrop> drops = new ArrayList<Raindrop>();
To make each drop fall,
for (int i=0; i<drops.length(); i++) {
drops.get(i).fall();
}

Here is my java (swing) implementation of 2d rain with drops, splash, wind and gravity
import java.awt.BasicStroke;
import java.awt.Color;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
import java.awt.geom.Ellipse2D;
import java.awt.geom.Line2D;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.Random;
import javax.swing.JFrame;
import javax.swing.JPanel;
public class Main {
public static void main( String [] args ) {
JFrame frame = new JFrame();
frame.setSize(800, 300);
final RPanel rPanel=new RPanel();
frame.add(rPanel);
frame.setVisible( true );
frame.addWindowListener(new WindowAdapter() {
#Override
public void windowClosing(WindowEvent e) {
super.windowClosing(e);
rPanel.stop();
System.exit(0);
}
});
}
}
class RPanel extends JPanel {
//*********SETTINGS****************************
private float mWind = 2.05f;
private float mGravity = 9.8f;
private double mRainChance = 0.99; // from 0 to 1
private int mRepaintTimeMS = 16;
private float mRainWidth=1;
private double mDdropInitialVelocity = 20;
private double mDropDiam = 2;
private Color mColor=new Color(0, 0, 255);
//*********************************************
private ArrayList<Rain> rainV;
private ArrayList<Drop> dropV;
private UpdateThread mUpdateThread;
public RPanel() {
rainV = new ArrayList<>();
dropV = new ArrayList<>();
mUpdateThread=new UpdateThread();
mUpdateThread.start();
}
public void stop() {
mUpdateThread.stopped=true;
}
public int getHeight() {
return this.getSize().height;
}
public int getWidth() {
return this.getSize().width;
}
private class UpdateThread extends Thread {
public volatile boolean stopped=false;
#Override
public void run() {
while (!stopped) {
RPanel.this.repaint();
try {
Thread.sleep(mRepaintTimeMS);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
}
#Override
public void paintComponent(Graphics g) {
super.paintComponent(g);
Graphics2D g2 = (Graphics2D) g;
g2.setStroke(new BasicStroke(mRainWidth));
g2.setColor(mColor);
//DRAW DROPS
Iterator<Drop> iterator2 = dropV.iterator();
while (iterator2.hasNext()) {
Drop drop = iterator2.next();
drop.update();
drop.draw(g2);
if (drop.y >= getHeight()) {
iterator2.remove();
}
}
//DRAW RAIN
Iterator<Rain> iterator = rainV.iterator();
while (iterator.hasNext()) {
Rain rain = iterator.next();
rain.update();
rain.draw(g2);
if (rain.y >= getHeight()) {
//create new drops (2-8)
long dropCount = 1 + Math.round(Math.random() * 4);
for (int i = 0; i < dropCount; i++) {
dropV.add(new Drop(rain.x, getHeight()));
}
iterator.remove();
}
}
//CREATE NEW RAIN
if (Math.random() < mRainChance) {
rainV.add(new Rain());
}
}
//*****************************************
class Rain {
float x;
float y;
float prevX;
float prevY;
public Rain() {
Random r = new Random();
x = r.nextInt(getWidth());
y = 0;
}
public void update() {
prevX = x;
prevY = y;
x += mWind;
y += mGravity;
}
public void draw(Graphics2D g2) {
Line2D line = new Line2D.Double(x, y, prevX, prevY);
g2.draw(line);
}
}
//*****************************************
private class Drop {
double x0;
double y0;
double v0; //initial velocity
double t; //time
double angle;
double x;
double y;
public Drop(double x0, double y0) {
super();
this.x0 = x0;
this.y0 = y0;
v0 = mDdropInitialVelocity;
angle = Math.toRadians(Math.round(Math.random() * 180)); //from 0 - 180 degrees
}
private void update() {
// double g=10;
t += mRepaintTimeMS / 100f;
x = x0 + v0 * t * Math.cos(angle);
y = y0 - (v0 * t * Math.sin(angle) - mGravity * t * t / 2);
}
public void draw(Graphics2D g2) {
Ellipse2D.Double circle = new Ellipse2D.Double(x, y, mDropDiam, mDropDiam);
g2.fill(circle);
}
}
}

You can use a particle system or use a vector of raindrops and animate them every X milliseconds. A link to a particle system library: http://code.google.com/p/jops/
example code for vector:
import java.util.Vector;
// In your class
Vector raindrops;
void animate()
{
ListIterator iter = raindrops.listIterator;
while (iter.hasNext()) {
((Raindrop)iter.next()).moveDown();
}
}

My for loop doesnt appear to run in my paint method

so im building brick breaker on Java and so far I have most of the UI done but Im having an issue with showing my bricks on my UI. I have written the code for it in my paint method which builds my panel and then my panel is added to a JFrame in another class. Everything shows except for my bricks and I cant seem to figure out why..
// AnimationPanel.java
//
// Informatics 45 Spring 2010
// Code Example: Our Ball Animation Becomes a Game
//
// This is relatively similar to our AnimationPanel in the previous version
// of our ball animation, with two changes:
//
// * The paddle is now drawn, in addition to just the ball. For fun, I've
// drawn the paddle in a different color than the ball.
//
// * This panel has a MouseMotionListener attached to it. The job of a
// MouseMotionListener is to listen for mouse movement within a component.
// In this case, any mouse movement within our AnimationPanel will turn
// into events, which we'll handle by adjusting the center x-coordinate
// of the paddle accordingly.
//
// * Because we need to calculate a new position for the paddle as the mouse
// moves, we'll need to be able to convert coordinates in both directions
// (i.e., fractional coordinates to pixel coordinates and pixel coordinates
// to fractional coordinates).
package inf45.spring2010.examples.animation2.gui;
import inf45.spring2009.examples.animation2.model.Animation;
import inf45.spring2009.examples.animation2.model.AnimationState;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class AnimationPanel extends JPanel
{
private Animation animation;
private inf45.spring2009.examples.animation2.model.AnimationState currentState;
boolean brickVisible[][];
int bricksInRow = 4;
int bricksInColumn = 8;
int brickWidth;
int brickHeight;
int bricksLeft;
public AnimationPanel(Animation animation)
{
this.animation = animation;
currentState = null;
setBackground(Color.WHITE);
addMouseMotionListener(
new MouseMotionAdapter()
{
public void mouseMoved(MouseEvent e)
{
updatePaddlePosition(e.getX());
}
});
}
public void updateState(AnimationState newState)
{
currentState = newState;
}
private void updatePaddlePosition(int pixelX)
{
double paddleCenterX = convertPixelXToX(pixelX);
animation.updatePaddleCenterX(paddleCenterX);
}
public void paint(Graphics g)
{
super.paint(g);
if (currentState == null)
{
return;
}
int centerPixelX = convertXToPixelX(currentState.getBallCenterX());
int centerPixelY = convertYToPixelY(currentState.getBallCenterY());
int radiusX = convertXToPixelX(currentState.getBallRadius());
int radiusY = convertYToPixelY(currentState.getBallRadius());
int topLeftPixelX = centerPixelX - radiusX;
int topLeftPixelY = centerPixelY - radiusY;
int paddleCenterPixelX = convertXToPixelX(currentState.getPaddleCenterX());
int paddleCenterPixelY = convertYToPixelY(currentState.getPaddleCenterY());
int paddleWidthPixels = convertXToPixelX(currentState.getPaddleWidth());
int paddleHeightPixels = convertYToPixelY(currentState.getPaddleHeight());
int paddleTopLeftPixelX = paddleCenterPixelX - (paddleWidthPixels / 2);
int paddleTopLeftPixelY = paddleCenterPixelY - (paddleHeightPixels / 2);
Graphics2D g2d = (Graphics2D) g;
/* for (int x = 0;x<bricksInRow;x++){
for (int y = 0;y<bricksInColumn;y++){
boolean bricks[][] = null;
brickVisible[x][y] = bricks[x][y] ;
{
g2d.setColor(Color.black);
g2d.fillRect(x*brickWidth,y*brickHeight,brickWidth-1,brickHeight-1);
}
}
}
*/
g2d.setRenderingHint(
RenderingHints.KEY_ANTIALIASING,
RenderingHints.VALUE_ANTIALIAS_ON);
g2d.setColor(Color.BLUE);
g2d.fillOval(topLeftPixelX, topLeftPixelY, radiusX * 2, radiusY * 2);
g2d.setColor(Color.RED);
g2d.fillRect(
paddleTopLeftPixelX, paddleTopLeftPixelY,
paddleWidthPixels, paddleHeightPixels);
}
private int convertXToPixelX(double x)
{
return (int) (x * getWidth());
}
private int convertYToPixelY(double y)
{
return (int) (y * getHeight());
}
private double convertPixelXToX(int pixelX)
{
return (double) pixelX / getWidth();
}
}

It seems like you don't assign any value to brickHeight and brickWidth in your code. This might be the problem.

What MByD said, although as these fields are package-local you could possibly be setting these elsewhere. Also, there is also a NPE problem here:
boolean bricks[][] = null;
brickVisible[x][y] = bricks[x][y] ;
I'm not sure if you added this in before or after you found things weren't working, but this is a sure-fire NullPointerException which will cause the rest of your paint code to not execute when thrown.
EDIT: I'm assuming you commented out the code that wasn't working, but this is the bit you want to make work.