I am wondering if there is a bit of code or that can apply a method from a class to all of the objects in the ArrayList? I'm making a basic space invaders program and I am trying to implement a move method that will apply to all of enemies, so that they move in a group rather than individually.
I've created the items in the array list here:
for (int i = 0; i < 6; i++) {
venWidth = venWidth - 139;
enemyList.add(new Venusian("/venusian.jpg", venWidth, height));
}
for (int i = 6; i < 12; i++) {
merWidth = merWidth - 145;
enemyList.add(new Mercurian("/mercurian.jpg", merWidth, merHeight));
}
for (int i = 12; i < 18; i++) {
marWidth = marWidth - 125;
enemyList.add(new Martian("/martian.jpg", marWidth, marHeight));
}
Here is where I call the move method:
for (int i = 0; i < enemyList.size(); i++) {
Invader Invaders = (Invader) enemyList.get(i);
Invaders.draw(g);
Invaders.Move(1024);
This makes them move independently and overlap, at the moment I am just moving them right and left using the boundaries of my created window. So is there any way of moving them together at the same time? I have searched for a way to apply a class method to all of the lists items but I haven't found anything after a couple of hours.
Any material, sources or advice relating to this would be greatly appreciated.
You will have to come up with a solution that can decouple the Invaders you are moving from those you are displaying.
This is due to the fact that your individual Invaders will always be more or less sequentially moved - even if you are working with multiple threads, etc. Even if you would start using Java8 Lambdas to write your code like this:
ArrayList<Invader> badGuys;
//fill your List here
badGuys.forEach( badGuy -> badGuy.move());
This would also create intermediate states where some Invaders were moved, some were not.
So you have to make sure that you only draw a consistent set of Invaders to your screen. You could do this several ways:
Only draw to screen after all Invaders were moved
Make a copy of your invaders for drawing, while the Invaders are being moved. After all Invaders were moved, start displaying the Invaders from the moved List
...
1st Edit: How do you draw the Invaders to screen? Is this happening in separate threads?
3rd EDIT: Okay so maybe you can stop your timerThread before starting to move your Invaders. And when you are finished with moving them you can restart the timer again. Check what methods your timer offers It should have start() and stop() or maybe suspend() methods.
Do something like this:
timer.stop();
badGuys.moveAll();
timer.start();
2nd EDIT: Just looked over your code again. There is no need for you to start your for loop number 2 and 3 from indexes other than 0. Your code will be easier to read if for example you just say:
for (int i = 0; i < 6; i++) { // start from 0 (to 6) instead of 6 to 12
merWidth = merWidth - 145;
enemyList.add(new Mercurian("/mercurian.jpg", merWidth, merHeight));
}
create an interface like Moveable. and put Move method on it. then implement it on Venusian, Martian and Mercurian. and use this interface on arraylist
interface Moveable {
public void Move(int dist);
}
class Mercurian implements Moveable {
public void Move(int dist)
{
//do something
}
}
class Venusian implements Moveable {
public void Move(int dist)
{
//do something
}
}
class Martian implements Moveable {
public void Move(int dist)
{
//do something
}
}
ArrayList<Moveable> enemyList = new ArrayList<Moveable>();
Related
OK, I'm in the process of making a simple java swing chess game. This question is more about OOP design then Java Swing.
I have the following:
I have a Panel class that implements JPanel.
I then have an abstract class Piece that extends from my Panel class
Then I have my classes for the different Pieces: Pawn, King, Bishop etc that extend from my Pieces class
In my main ChessGame Class:
I am using an array of Panel to store the layout of my board
So the array will store, Panel objects, for board places with no pieces on it.
And it will store, the subclasses such as Pawn, Queen, Bishop etc (board places with pieces)
So, the top left square (0,0) maps to myArray[0][0]
My problem is that, to check if the place is empty or has chess pieces in it I have to use:
if(panels[x][y] instanceof Piece){
((Piece)panels[x][y]).makeMove();
}
What I'm asking is this terrible design? I know I should try and stay away from instanceof.
What would be a better approach?
Thanks.
You shouldn't combine the Model code (Piece) with the view code (JPanels). If you ever want to change how the board is displayed you have to change how pieces are stored!
A better design might be to separate Piece from JPanels. Then you can use a single JPanel to display a matrix of Pieces : Pieces[8][8].
My problem is that, to check if the place is empty or has chess pieces in it I have to use:
If you use a matrix, you can just have a null cell or use the Null Object Pattern to have an "empty" piece.
EDIT
Each cell in the piece matrix is a square in the board so piece[0][0] would be the top corner of the board (A8).
To paint the board your paintComponent() method would have to iterate over this matrix and draw each cell appropriately. There are several ways to implement this:
You would need to do a similar instanceof check to draw each type of piece differently
Make a new intermediate "paint strategy" object using the strategy pattern. This may require a matrix of strategy objects instead of piece objects. You may still need to do instance of checks, but maybe only the once to create the strategy objects.
After considering your problem, and knowing the problem domain, I would actually suggest the following...
In your class Panel implement a function int hasMass() as follows...
public int hasMass() {
return 0;
}
In your class Piece override that function as follows...
public int hasMass() {
if (isWhite()) // white pieces are negative.
return -1;
return 1; // black pieces positive.
}
Now you can check if the square has a piece, whether another given piece could take it... (because they have opposite polarity)... e.g. mass + mass == 0 means a capture, != 0 means the panel was empty. And of course an absolute value of 2 (for mass) would mean the move was illegal.
OK, ill start by throwing away the option of setting null to indicate that place is empty (you can do it ofc but using the Empty class is just 'better' in a way).
So let's say you have array of Panels representing your game board:
Panel[][] board;
Now for ilustration, how your class hierarchy could look like:
abstract class Panel extends JPanel { ... }
class Empty extends Panel { ... }
abstract class Piece extends Panel { ... }
class Pawn extends Piece { ... }
...
My Panel class is my Empty class is it not?
Not sure if i understand you, but let's have a look on what extends means exactly: in the show nmodel every Piece is also a Panel or every Pawn is also a Piece, so every Pawn can do all the same things as Piece (for example, 4 is complex number as well as natural number or real number, so in a way, you could say that real numbers extend complex numbers, since every real number is also a complex number)
So now you can have some nice abstract getTexture() method declared in Panel implemenented in Empty class and in all Piece subclasses, and when drawing a Panel, you dont need to look if it is empty or not.
Instead of creating (I assume) almost identical classes for each piece (Rook, Pawn, Queen etc.), you could just keep the original Piece class, make it non abstract and add a PieceType field to it. PieceType is just an enum that tells what type of piece (if any) is placed there. Instead of using instanceof, now you can check using panels[i][j].getType() == PieceType.ROOK. At least that's what I'm doing in my implementation :)
I'm also using JLabel instead of JPanel for my 8x8 board.
Instead of splitting panel to 8x8 smaller panels, you must draw the board and the pieces on a canvas. Later the players will eventually be dragging to move pieces on board. Also you could look for Bitboard presentation in chess game, although this presentation is only required for chess engines which are able to "think" for fast calculations, it is still useful when you have to check if the move that player is trying to make is correct.
Posible Bitboard:
public class BitBoard
{
public static final int P = 0;
public static final int N = 2;
public static final int B = 4;
public static final int R = 6;
public static final int Q = 8;
public static final int K = 10;
public static final int p = 1;
public static final int n = 3;
public static final int b = 5;
public static final int r = 7;
public static final int q = 9;
public static final int k = 11;
// empty field
public static final int empty = 12;
// number of pieces , squares
public static final int nPieces = 12;
public static final int nSquares = 64;
public static final int whitePieces = 12;
public static final int blackPieces = 13;
public static final int nBoards = 14;
public static long squareBits[];
// static member initialization
static
{
squareBits = new long[64];
long square = 1;
square = square << 8 * 8 - 1;
for (int i = 0; i < 64; i++) {
squareBits[i] = square >>> i;
}
}
long bitBoards[];
public BitBoard() {
bitBoards = new long[nBoards];
}
public boolean initBoard()
{
// Put the pieces on the board
EmptyBoard();
addPiece(0, r);
addPiece(1, n);
addPiece(2, b);
addPiece(3, q);
addPiece(4, k);
addPiece(5, b);
addPiece(6, n);
addPiece(7, r);
for (int i = 8; i < 16; i++) {
addPiece(i, p);
}
for (int i = 48; i < 56; i++) {
addPiece(i, P);
}
addPiece(56, R);
addPiece(57, N);
addPiece(58, B);
addPiece(59, Q);
addPiece(60, K);
addPiece(61, B);
addPiece(62, N);
addPiece(63, R);
return true;
}
public boolean addPiece(int whichSquare, int whichPiece)
{
bitBoards[whichPiece] |= squareBits[whichSquare];
bitBoards[nPieces + (whichPiece % 2)] |= squareBits[whichSquare];
return true;
}
private boolean removePiece(int whichSquare, int whichPiece)
{
bitBoards[whichPiece] ^= squareBits[whichSquare];
bitBoards[nPieces + (whichPiece % 2)] ^= squareBits[whichSquare];
return true;
}
private boolean EmptyBoard()
{
for (int i = 0; i < nBoards; i++)
{
bitBoards[i] = 0;
}
return true;
}
}
I would keep a structure of the pieces separate from the rendered board.
For example, I would make the chess pieces pure models w/o knowledge of hit they're rendered.
Pieces (baseclass)
+- Pawn
+- Knight
+- King
+- Queen
+- ..etc
This will allow you to keep an array of Pieces only, where empty squares are null.
For simplicity sake, I'd just have a matrix of peices:
Peices[][] board = new Pieces[8][8];
(of course an initialization method to traverse your 'board' and populate the board w/ the initial positions)
I would then have a visible board constructed of JPanels; a class called "Chess" to manage game; and the actual rendering of the tile/panel in the move function. Imagine:
// what a move might look like when initializing your panels
piece = board [0][0];
Chess.move(piece, 0 ,0); //responsible for clearing the old panel and rendering the panel at target location.
When the user interacts w/ your game..they click your panels..which will give you the panel coordinates. You use the same coordinates w/ your 'board' to determine what the piece is..how it can move etc..
Something like that...
I would just represent the game board using objects...for simplicity. Easiest to understand..and besides..computers are plenty fast now.
Ok so my understanding of methods is not at it's best, so I'm here.
So the goal of is to build a pyramid based off a triangle. In drawTriangle I create a triangle, and now I must multiple it one by one for each layer. Top layer would have one triangle...second layer would have two triangles...third would have three...you get the picture.
private void drawTriangle () {
for (int x=0; x<3; x++) { //draws triangle
yertle.penDown();
yertle.left(2*PI/3);
yertle.forward(20);
}
}
private void drawPyramind (int n) { //n being layers
for (int nTri=0; nTri<n; nTri++) { //nTri being copies of triangle
drawTriangle(nTri); //what I _thought_ would work
... //irrelevant code to line up layers
... //
}
}
But I'm unsure how I should copy the drawTriangle method into drawPyramid method.
IMPORTANT: However this is an assignment and I don't want a direct answer, just a hint of how I should be doing this to help my understanding of methods.
I'm trying to make a tower defense game. So far I've made the JFrame (called GameFrame) where everything is displayed, added a background image (.PNG) and I'm trying to create the monsters and make them "move" over the path I've created. So, I created a GlassPane class which I set as glassPane in the GameFrame.
Here is the code for the GlassPane:
public class GlassPane extends JComponent implements ActionListener{
private ArrayList<MyPoint> path; //list of Points-pixel positions- (x,y pair) that monsters will follow
private ArrayList<Monster> wave; //list of monsters that will try to reach the rift
private Timer timer; //javax.swing.Timer
private boolean waveEnd;//signing that the wave has ended(ignore it)
public GlassPane(){
super();
createPath();//method is below
wave = new ArrayList<Monster>();//monsters added in nextWave()
timer = new Timer(4,this);//timer in order to slow down and smooth the movement of monsters
waveEnd = false;
}
#Override
protected void paintComponent(Graphics g){
super.paintComponent(g);
for(Monster m:wave){
if(m.isVisible())//visible is a private variable in Monster class(defines whether i want to paint that monster or not)
{
g.drawImage(m.getImage(), m.getX(), m.getY(), this);
}
}
}
public void nextWave(){
waveEnd = false;
for(int i =0;i<20;i++)
wave.add(new Monster());
wave.get(0).setVisible(true);//sets the first monster to be visible(paintable)
int visibles = 1;//index 0 is visible,so index 1 is next to become visible
while(!waveEnd){
if(visibles<19 && wave.get(0).getPathIndex()%50 == 0){
//meaning until all 20 monsters are visible(indexes 0-19),"every 50 steps(pixels) the first monster moves"
wave.get(visibles).setVisible(true);
//make another monster visible and start moving it
visibles++;//visible(moving) monsters increased by 1
timer.start();//"move all visible monsters one step forward with a small delay until the next movement to make it soft"
}
JOptionPane.showMessageDialog(new JFrame(), "Finished!","All monsters reached the rift!",JOptionPane.INFORMATION_MESSAGE);//let me know then wave is finished
}
private void createPath(){
//just making a lsit of pixels that I want monsters to follow
path = new ArrayList<MyPoint>();
for(int x=0;x<175;x++){
path.add(new MyPoint(x,0));
}
for(int y=0;y<175;y++){
path.add(new MyPoint(174,y));
}
for(int x=175;x<325;x++){
path.add(new MyPoint(x,174));
}
for(int y=175;y<425;y++){
path.add(new MyPoint(299,y));
}
for(int x=325;x<575;x++){
path.add(new MyPoint(x,424));
}
for(int y=424;y>175;y--){
path.add(new MyPoint(574,y));
}
for(int x=575;x<1001;x++){
path.add(new MyPoint(x,174));
}
}
#Override
public void actionPerformed(ActionEvent arg0) {
for(Monster m:wave)
if(m.isVisible())
m.move(path);
//"move every visible monster by one step"
if(m.get(19).getPathIndex() == 1674)//1674 is the path's last index
waveEnd = true;//if the last monster reaches the end,then all have
//meaning the wave is finished
this.repaint();//refresh any changes to the monsters' positions
}
}
The problem is that only the first monster is moving through the path, meaning only that one is painted when I invoke repaint(). What am I doing wrong in paintComponent(Graphics g)? Because I believe that's where my mistake is... How can I draw all "available" images each time one after another?
Note: They are buffered images in .PNG format if that matters at all.
I though about adding the Monster class code but I believe explaining the methods' function is enough to understand what's going on. Should someone need more details let me know. Thanks in advance.
I think you have to put parantheses around your loops.
The shorthand only loops over the first line after the loop
//Output:
//AAAAAAAAAAAAAAAAAA
//AAAAAAAAAAAAAAAAAA
//AAAAAAAAAAAAAAAAAA
//AAAAAAAAAAAAAAAAAA
//BBBBBBBBBBBBBBBBBB
for(Monster m:wave)
System.out.println("AAAAAAAAAAAAAA");
System.out.println("BBBBBBBBBBBBBBB");
//Output:
//AAAAAAAAAAAAAAAAAA
//AAAAAAAAAAAAAAAAAA
//AAAAAAAAAAAAAAAAAA
//AAAAAAAAAAAAAAAAAA
//BBBBBBBBBBBBBBBBBB
//BBBBBBBBBBBBBBBBBB
//BBBBBBBBBBBBBBBBBB
//BBBBBBBBBBBBBBBBBB
for(Monster m:wave)
{
System.out.println("AAAAAAAAAAAAAA");
System.out.println("BBBBBBBBBBBBBBB");
}
I am trying to replicate the applet found here as a part of an exercise. The applet is using Fortune's algorithm to generate both; a Voronoi diagram and Delaunay triangulation. I am just interested in generating the Delaunay Triangulation in a plane and thus, would be using the incremental algorithms i.e. adding 1 point at a time. I intend to show the triangles being generated at every stage when a sample point is added.
I am using a SwingWorker class to create an instance of the Triangulate class which contains the algorithm. I am calling the triangulate method inside a for loop which iterates through the set of sample points when the start button on the GUI is clicked.
Here's the code for that:
JButton startButton = new JButton("Start");
startButton.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent ae) {
SwingWorker<List<Triangle>, Triangle> worker = new SwingWorker<List<Triangle>, Triangle>() {
#Override
protected List<Triangle> doInBackground() throws Exception {
Triangulate dt = new Triangulate(drawingPanel.pointsList());
dt.preTriangulate(); //Set-up a bounding triangle and obtain a random permutation of the points
List<PlanarPoint> pointsList = dt.pointsList();
for (int i = 0; i < pointsList.size(); i++) {
PlanarPoint sample = pointsList.get(i);
dt.triangulate(sample);
List<Triangle> list = dt.trianglesList(); //Obtaining the list of triangles at every stage. Good Idea??
for (int j = 0; j < list.size(); j++) {
publish(list.get(j));
}
Thread.sleep(500);
}
dt.removeTriangles(dt.trianglesList()); // Remove all the triangles containing bounding-triangle vertices
return dt.trianglesList();
}
protected void process(List<Triangle> triangles) {
for (Triangle triangle : triangles) {
g = drawingPanel.getGraphics();
PlanarPoint p1 = triangle.getVertex1();
PlanarPoint p2 = triangle.getVertex2();
PlanarPoint p3 = triangle.getVertex3();
g.drawLine((int) Math.ceil(p1.x), (int) Math.ceil(p1.y),
(int) Math.ceil(p2.x), (int) Math.ceil(p2.y));
g.drawLine((int) Math.ceil(p2.x),(int) Math.ceil(p2.y),
(int) Math.ceil(p3.x),(int) Math.ceil(p3.y));
g.drawLine((int) Math.ceil(p3.x),(int) Math.ceil(p3.y),
(int) Math.ceil(p1.x),(int) Math.ceil(p1.y));
}
}
};
worker.execute();
}
});
Here is the Triangulate class which computes a Delanuay Triangulation of a set of points:
public class Triangulate {
private List<PlanarPoint> pointsList;
private List<Triangle> triangleList;
private Triangle boundingTriangle;
private List<Edge> edgeList;
public Triangulate(List<PlanarPoint> pointsList) {
this.pointsList = pointsList;
this.triangleList = new ArrayList<Triangle>();
this.edgeList = new ArrayList<Edge>();
}
public List<Triangle> trianglesList() {
return triangleList;
}
public List<PlanarPoint> pointsList() {
return pointsList;
}
public void preTriangulate() {
boundingTriangle = getBoundingTriangle(pointsList);
triangleList.add(boundingTriangle);
randomPermutation(pointsList);
}
public void triangulate(PlanarPoint samplePoint) {
// A procedure implementing the Bowyer - Watson algorithm
// to calculate the DT of a set of points in a plane.
}
public void removeTriangles(List<Triangle> trianglesList) {
// A procedure to remove all triangles from the list sharing
// edges with the bounding-triangle
}
private Triangle getBoundingTriangle(List<PlanarPoint> pointsList) {
//Obtains a bounding-triangle for a set of points
}
public void randomPermutation(List<PlanarPoint> pointsList) {
//Obtains a random permutation of a set of points
}
}
I have 3 other classes
PlanarPoint - sub-class of Point2D.Double which implements Comparable to provide a y-co-ordinate based sorting
Triangle - A class which determines a circum-circle and circum-radius for the triangle and determines whether a point lies inside the circumcircle of the triangle
Edge - A class which represents Edge as the one having 2 PlanarPoints as its end-points.
DrawingPanel - A class which acts as the surface on which points are added at click events and drawn on the screen.
Now, here are a few concerns which I have
Is there a better way to show the triangles and possibly circum-circles by iterating over a set of points and then calling a function of the Triangulate class to get the existing circum-circles and triangles
Should all the drawing be restricted to the DrawingPanel class since in the code snippets above I am painting in the class which extends JApplet/JFrame and thus whenever the window is resized, the drawn triangles are lost? Is there a design pattern which I can follow?
Is the usage of SwingWorker over spawning another thread justified over here except for the fact that the time to compute the DT of a set of points is a time-consuming task?
If I have missed any details, please let me know
Thanks,
Chaitanya
Suggestions:
Don't use getGraphics() to get a Graphics object since the Graphics object obtained won't persist if any repaint is performed (something out of your control). Instead draw to a BufferedImage and have the JPanel or JComponent draw the BufferedImage in its paintComponent override, or add your image data to a Collection of some sort, and have the paintComponent override method iterate through the Collection using the information to draw your images.
Don't draw directly in a top level window such as a JFrame or JApplet, but instead in a component that derives from JComponent, often either JComponent itself or JPanel.
Read the Swing graphics tutorials as they will explain all of this and more.
SwingWorker is fully justified since you want to create a thread that is background to a Swing application yet interacts with the Swing application -- the very situation that SwingWorkers were created for.
So I'm just messing around learning to create a Space invaders type game. I can get the bad guys to move, Great!!. Hero moves, Great!! Bullets move, Great!! However I try to remove my bullets once they leave the screen as to not eat up all resources and it force closes on me once it gets rid of the bullet. It goes off the screen. Hits the int of -2 and then we use the remove() and boom. Force Close.
Here is my code. I'm wondering if they access the size() at the same time and just cause a force close because of it.
//I removed everything that doesn't pertane to the bullets.
public class GameScreen{
Bullet bullet = world.bullet;
public GameScreen(Game game) {
super(game);
world = new World();
}
//Draws our bullets.
int bulletLength = bullet.bullets.size();
for(int i = 0; i < bulletLength; i++) {
Placement part = bullet.bullets.get(i);
x = part.x * 32 + 11;
y = part.y * 32;
g.drawPixmap(Assets.bullet, x, y);
}
Class that holds my bullets.
public class Bullet {
public List<Placement> bullets = new ArrayList<Placement>();
public Bullet() {
}
public void shoot(int x, int y){
bullets.add(new Placement(x,y));
}
public void advance(){
int len = bullets.size(); // gets all bullets.
for(int i = 0; i < len; i++) {
bullets.get(i).y --;
if (bullets.get(i).y <= -2){//removes them once they are off the screen.
bullets.remove(i);
}
}
}
This is what I use to keep track of placement.
package com.learning.planecomander;
public class Placement {
public int x, y;
public Placement(int x, int y) {
this.x = x;
this.y = y;
}
}
When going through your list to remove bullets, you can remove bullets from a list but that affects the list immediately instead of after your loop is done. Since you are traversing to the length of the list at the start, you are going off the end of the list since you've removed elements. An example is probably more helpful than that description.
Let's say you have a list with three bullets (which I'll call a, b, c to make the example easier). On a pass through the list, a and c are fine but b needs to be removed.
i = 0;
bullets[0] = a;
bullets[1] = b;
bullets[2] = c;
First loop goes fine, second loop starts like this
i = 1;
bullets[0] = a;
bullets[1] = b;
bullets[2] = c;
We remove b, but the loop keeps going
i = 2;
bullets[0] = a;
bullets[1] = c;
OH CRAP ARRAYINDEXOUTOFBOUNDS! PROGRAM CRASHES!
The way to solve this is to use a temp list to store the bullets that need to be removed, and then once your update loop is finished, make a call to bullets.removeAll(temp)
Doing two passes is a good answer. It makes the loops simpler and easy to understand. If you'd like to do it in one pass though, iterate through the list in reverse order, and when you remove a bullet you can go to the next one and not worry about blasting past the end of the ArrayList.
Alternatively, you can keep your bullets in a linked list, and run through the list with an Iterator, which you can also use to remove items from the list with. Removing from the beginning middle or end of an linked list is always a constant time operation. Whereas removing from the beginning of an ArrayList can be more expensive. If you need random access to the elements in the list, then they can be inefficient. Keep in mind though, if you're only dealing with a handful of objects, then it doesn't really matter.
For bonus points, you might want to put all of your objects in a list, and then have your central loop process them all and have your game objects respond polymorphically to calls like dead?, think, move, draw or whatever you think is appropriate.