Thread: how can i set an object in focus

There is a Canvas object in my game and this object is not set in focus, because of this my snake is not moving on the Board .

Basically i am working on snake game project, and i want is when play button is clicked from PlayGame.java JDialog ,game should start ,but problem i am facing is after clicking button gamescreen appearing on window but snake is not moving, so someone suggest me that your canvas object is not in focus whenever it is called. that is why KeyLisener not able to listen to keyPresses /key strokes.

This is the class in which canvas object is declared and implemented.

package org.psnbtech;
 
import java.awt.Canvas;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Font;
import java.awt.Graphics2D;
import java.awt.RenderingHints;
import java.awt.event.KeyAdapter;
import java.awt.event.KeyEvent;
import javax.swing.JFrame;
import org.psnbtech.GameBoard.TileType;
import org.psnbtech.Snake.Direction;
 
 
public class Engine extends KeyAdapter {
 
    private static final int UPDATES_PER_SECOND = 15;
 
    private static final Font FONT_SMALL = new Font("Arial", Font.BOLD, 20);
 
    private static final Font FONT_LARGE = new Font("Arial", Font.BOLD, 40);
 
    public Canvas canvas;
 
    public GameBoard board;
 
    public Snake snake;
 
    public int score;
 
    public boolean gameOver;
 
 
    public Engine(Canvas canvas) {
                this.canvas = canvas;
            this.board = new GameBoard();
        this.snake = new Snake(board);
 
        resetGame();
 
        canvas.addKeyListener(this);
                //new Engine(canvas).startGame();
    }
 
 
    public void startGame() {
        canvas.createBufferStrategy(2);
 
        Graphics2D g = (Graphics2D)canvas.getBufferStrategy().getDrawGraphics();
        g.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
 
        long start = 0L;
        long sleepDuration = 0L;
        while(true) {
            start = System.currentTimeMillis();
 
            update();
            render(g);
 
            canvas.getBufferStrategy().show();
 
            g.clearRect(0, 0, canvas.getWidth(), canvas.getHeight());
 
            sleepDuration = (1500L / UPDATES_PER_SECOND) - (System.currentTimeMillis() - start);
 
            if(sleepDuration > 0) {
                try {
                    Thread.sleep(sleepDuration);
                } catch(Exception e) {
                                    e.printStackTrace();
                }
            }
        }
    }
 
    public void update() {
        if(gameOver || !canvas.isFocusable()) {
            return;
        }
        TileType snakeTile = snake.updateSnake();
        if(snakeTile == null || snakeTile.equals(TileType.SNAKE)) {
            gameOver = true;
        } else if(snakeTile.equals(TileType.FRUIT)) {
            score += 10;
            spawnFruit();
        }
    }
 
    public void render(Graphics2D g) {
        board.draw(g);
 
        g.setColor(Color.WHITE);
 
        if(gameOver) {
            g.setFont(FONT_LARGE);
            String message = new String("Your Score: " + score);
            g.drawString(message, canvas.getWidth() / 2 - (g.getFontMetrics().stringWidth(message) / 2), 250);
 
            g.setFont(FONT_SMALL);
            message = new String("Press Enter to Restart the Game");
            g.drawString(message, canvas.getWidth() / 2 - (g.getFontMetrics().stringWidth(message) / 2), 350);
        } else {
            g.setFont(FONT_SMALL);
            g.drawString("Score:" + score, 10, 20);
        }
    }
 
    public void resetGame() {
        board.resetBoard();
        snake.resetSnake();
        score = 0;
        gameOver = false;
        spawnFruit();
    }
 
    public void spawnFruit() {
        int random = (int)(Math.random() * ((GameBoard.MAP_SIZE * GameBoard.MAP_SIZE) - snake.getSnakeLength())); // if '*' replace by '/' then only one fruit is there for snake
 
        int emptyFound = 0;
        int index = 0;
        while(emptyFound < random) {
            index++;
            if(board.getTile(index % GameBoard.MAP_SIZE, index / GameBoard.MAP_SIZE).equals(TileType.EMPTY)) { // if '/' replaced by '*' then nothing displays on the board 
                emptyFound++;
            }
        }
        board.setTile(index % GameBoard.MAP_SIZE, index / GameBoard.MAP_SIZE, TileType.FRUIT); // it also show nothing when replacing '/' by '/' 
    }
 
    @Override
    public void keyPressed(KeyEvent e) {
        if((e.getKeyCode() == KeyEvent.VK_UP)||(e.getKeyCode() == KeyEvent.VK_W)) {
            snake.setDirection(Direction.UP);
        }
        if((e.getKeyCode() == KeyEvent.VK_DOWN)||(e.getKeyCode() == KeyEvent.VK_S)) {
            snake.setDirection(Direction.DOWN);
        }
        if((e.getKeyCode() == KeyEvent.VK_LEFT)||(e.getKeyCode() == KeyEvent.VK_A)) {
            snake.setDirection(Direction.LEFT);
        }
        if((e.getKeyCode() == KeyEvent.VK_RIGHT)||(e.getKeyCode() == KeyEvent.VK_D)) {
            snake.setDirection(Direction.RIGHT);
        }
        if(e.getKeyCode() == KeyEvent.VK_ENTER && gameOver) {
            resetGame();
        }
    }
 
         public static void main(String[] args)  {
        new PlayGame().setVisible(true);
 
        /**JFrame frame = new JFrame("SnakeGame");
        frame.setDefaultCloseOperation(JFrame.HIDE_ON_CLOSE);
        frame.setResizable(false);
 
        Canvas canvas = new Canvas();
        canvas.setBackground(Color.black);
        canvas.setPreferredSize(new Dimension(GameBoard.MAP_SIZE * GameBoard.TILE_SIZE, GameBoard.MAP_SIZE * GameBoard.TILE_SIZE));
 
        frame.getContentPane().add(canvas);
        frame.pack();
        frame.setLocationRelativeTo(null);
        frame.setVisible(true); 
 
        new Engine(canvas).startGame();*/
 
 
             }        
}

And also i am attching actionPerformed() method of Play Button where i am referring canvas object

private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {                                         
    JFrame frame = new JFrame("SnakeGame"); 
    frame.setDefaultCloseOperation(JFrame.HIDE_ON_CLOSE);
    frame.setResizable(false);
 
    Canvas canvas = new Canvas();
    canvas.setBackground(Color.black);
    canvas.setPreferredSize(new Dimension(GameBoard.MAP_SIZE *GameBoard.TILE_SIZE,GameBoard.MAP_SIZE * GameBoard.TILE_SIZE));
 
    frame.add(canvas);
    frame.pack();
    frame.setLocationRelativeTo(null);
    frame.setVisible(true); 
 
    new Engine(canvas).startGame();
 
    }

--- Update ---

So please tell/suggest me how can i set canvas object in focus

Actually this project Contain five java files .i show this code because it almost contaiinng most of the logic of snake game.
five classes: 1. Engine.java
2. Snake.java (declaring an enum Direction and updateSnake() , resetGame() method, setDirection())
3. GameBoard.java (having enum TileType(Snake,Fruit,Empty) resetBoard() method ,setTile(), getTile(), draw() methods)
4. PlayGame.java(is a JDialog, having three button Play button, Rules button, exit button and corresponding action)
5. Rules.java (is a JDialog, have a single button when clicked return to playgame.java form )

note: when play button gets clicked it should start the game ,the action is working but problem is snake is not moving
so plz suggest some thing

--- Update ---

i will show u some code too

Snake.java

 
package org.psnbtech;
 
import java.awt.Canvas;
import java.awt.Point;
import java.util.LinkedList;
 
import org.psnbtech.GameBoard.TileType;
 
public class Snake {
	public Canvas canvas;
	public static enum Direction {
 
		UP,
 
		DOWN,
 
		LEFT,
 
		RIGHT,
 
		NONE
 
	}
 
	public Direction currentDirection;
 
	public Direction temporaryDirection;
 
	public GameBoard board;
 
	public LinkedList<Point> points;
 
 
        public Snake(GameBoard board) {
		this.canvas = canvas;
                this.board = board;
		this.points = new LinkedList<Point>();
 
        }
 
	public void resetSnake() {		
		this.currentDirection = Direction.NONE;
		this.temporaryDirection = Direction.NONE;
 
		Point head = new Point(GameBoard.MAP_SIZE / 2, GameBoard.MAP_SIZE / 2);
		points.clear();
		points.add(head);
		board.setTile(head.x, head.y, TileType.SNAKE);		
	}
 
	public void setDirection(Direction direction) {
		if(direction.equals(Direction.UP) && currentDirection.equals(Direction.DOWN)) {
			return;
		} else if(direction.equals(Direction.DOWN) && currentDirection.equals(Direction.UP)) {
			return;
		} else if(direction.equals(Direction.LEFT) && currentDirection.equals(Direction.RIGHT)) {
			return;
		} else if(direction.equals(Direction.RIGHT) && currentDirection.equals(Direction.LEFT)) {
			return;
		}
		this.temporaryDirection = direction;
	}
 
	public TileType updateSnake() {
		this.currentDirection = temporaryDirection;
 
		Point head = points.getFirst();	
 
		switch(currentDirection) {
 
		case UP:
			if(head.y <= 0) {
				return null;
			}
			points.push(new Point(head.x, head.y - 1));
			break;
 
		case DOWN:
			if(head.y >= GameBoard.MAP_SIZE - 1) {
				return null;
			}
			points.push(new Point(head.x, head.y + 1));
			break;
 
		case LEFT:
			if(head.x <= 0) {
				return null;
			}
			points.push(new Point(head.x - 1, head.y));
			break;
 
		case RIGHT:
			if(head.x >= GameBoard.MAP_SIZE - 1) {
				return null;
			}
			points.push(new Point(head.x + 1, head.y));
			break;
 
		case NONE:
			return TileType.EMPTY;
		}
 
		head = points.getFirst();
 
		TileType oldType = board.getTile(head.x, head.y);
		if(!oldType.equals(TileType.FRUIT)) {
			Point last = points.removeLast();
			board.setTile(last.x, last.y, TileType.EMPTY);
			oldType = board.getTile(head.x, head.y);
		}
 
		board.setTile(head.x, head.y, TileType.SNAKE);
 
		return oldType;
	}
 
	public int getSnakeLength() {
		return points.size();
	}
 
	public Direction getCurrentDirection() {
		return currentDirection;
	}
 
}

GameBoard.java

package org.psnbtech;
 
import java.awt.Color;
import java.awt.Graphics2D;
 
public class GameBoard {
 
	public static final int TILE_SIZE  = 20;
 
	public static final int MAP_SIZE = 30;
 
	public static enum TileType {
 
		SNAKE(Color.GREEN),
 
		FRUIT(Color.orange),
 
		EMPTY(null);
 
 
            public Color tileColor;
 
		private TileType(Color color) {
			this.tileColor = color;
		}
 
		public Color getColor() {
			return tileColor;
		}
 
	}
 
	private TileType[] tiles;
 
	public GameBoard() {
		tiles = new TileType[MAP_SIZE * MAP_SIZE];
	}
 
	public void resetBoard() {
		for(int i = 0; i < tiles.length; i++) {
			tiles[i] = TileType.EMPTY;
		}
	}
 
	public void setTile(int x, int y, TileType type) {
		tiles[y * MAP_SIZE + x] = type;
	}
 
	public TileType getTile(int x, int y) {
		return tiles[y * MAP_SIZE + x];
	}
 
	public void draw(Graphics2D g) {
		g.setColor(TileType.SNAKE.getColor());
 
		for(int i = 0; i < tiles.length; i++) {
			int x = i % MAP_SIZE;
			int y = i / MAP_SIZE;
 
			if(tiles[i].equals(TileType.EMPTY)) {
				continue;
			}
 
			if(tiles[i].equals(TileType.FRUIT)) {
				g.setColor(TileType.FRUIT.getColor());
				g.fillOval(x * TILE_SIZE + 4, y * TILE_SIZE + 4, TILE_SIZE - 8, TILE_SIZE - 8);
				g.setColor(TileType.SNAKE.getColor());
			} else {
				g.fillRect(x * TILE_SIZE + 1, y * TILE_SIZE + 1, TILE_SIZE - 2, TILE_SIZE - 2);
			}
		}
	}
 
}

--- Update ---

plz if u can look up the code

I have downloaded a snake game project from the internet, initially this project contains three java files namely
1. Engine.java
2. Snake.java
3. Gameoard.java

when i runs Engine.java ,game starts running ..

Now i have done some modification in it to improve the interactivity of the game, i.e i have added two #JDialog named

PlayGame.java

, and

RulesDialog.java

.

PlayGame.java has three JButtons :- Play button, Rules Button , Exit

when

play

button gets clicked game should start
when

rules

button gets clicked

RulesDialog.java JDialog

appears and when

exit button

gets clicked application or game should be closed.

Action of button is set in the actionPerformed() method of individual buttons.
Now

problem

i am facing is when i click

Play button

g

ame window is visible on the screen but snake is not moving

.

and i am not getting to point how to resolve this problem ..
So plz help me out

--- Update ---

I have downloaded a snake game project from the internet, initially this project contains three java files namely
1. Engine.java
2. Snake.java
3. Gameoard.java

when i runs Engine.java ,game starts running ..

Now i have done some modification in it to improve the interactivity of the game, i.e i have added two #JDialog named
1. PlayGame.java

2. RulesDialog.java

PlayGame.java has three JButtons :- Play button, Rules Button , Exit

-when play button gets clicked game should start

-when rules button gets clicked RulesDialog.java JDialog appears and when

-exit button gets clicked application or game should be closed.

Action of button is set in the actionPerformed() method of individual buttons.

Now problem i am facing is when i click Play button game window is visible on the screen but snake is not moving

and i am not getting to point how to resolve this problem ..

So plz help me out

can u please elaborate what u want from me because i am not getting your point.

Ok. there is Engine.java class in my project which has almost all the methods to handle the game.
So i am sendig u Engine.class . Or if u can say i will mail my project to you.

package org.psnbtech;
 
import java.awt.Canvas;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Font;
import java.awt.Graphics2D;
import java.awt.RenderingHints;
import java.awt.event.KeyAdapter;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import javax.swing.JFrame;
import org.psnbtech.GameBoard.TileType;
import org.psnbtech.Snake.Direction;
 
 
public  class Engine extends KeyAdapter implements KeyListener  {
 
	private static final int UPDATES_PER_SECOND = 15;
 
	private static final Font FONT_SMALL = new Font("Arial", Font.BOLD, 20);
 
	private static final Font FONT_LARGE = new Font("Arial", Font.BOLD, 40);
 
	public Canvas canvas;
 
	public GameBoard board;
 
	public Snake snake;
 
	public int score;
 
	public boolean gameOver;
 
        public boolean isOver;   
    private Graphics2D g;
 
 
        @SuppressWarnings("LeakingThisInConstructor")
	public Engine(Canvas canvas) {
 
                this.canvas = canvas;
        	this.board = new GameBoard();
		this.snake = new Snake(board);
 
		resetGame();
 
		canvas.addKeyListener(this);
 
                //new Engine(canvas).startGame();
	}
 
 
 
	public void startGame() {
		canvas.createBufferStrategy(2);
                canvas.setFocusable(true);
 
		Graphics2D g = (Graphics2D)canvas.getBufferStrategy().getDrawGraphics();
		g.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
 
		long start = 0L;
		long sleepDuration = 0L;
		while(true) {
			start = System.currentTimeMillis();
 
			update();
			render(g);
 
			canvas.getBufferStrategy().show();
 
			g.clearRect(0, 0, canvas.getWidth(), canvas.getHeight());
 
			sleepDuration = (1500L / UPDATES_PER_SECOND) - (System.currentTimeMillis() - start);
 
			if(sleepDuration > 0) {
				try {
					Thread.sleep(sleepDuration);
				} catch(Exception e) {
                                    e.printStackTrace();
				}
			}
		}
	}
 
	public void update() {
		if(gameOver || !canvas.isFocusable()) {
			return;
		}
                canvas.setFocusable(true);
		TileType snakeTile = snake.updateSnake();
		if(snakeTile == null || snakeTile.equals(TileType.SNAKE)) {
			gameOver = true;
		} else if(snakeTile.equals(TileType.FRUIT)) {
			score += 10;
			spawnFruit();
		}
	}
 
	public void render(Graphics2D g) {
		board.draw(g);
 
		g.setColor(Color.WHITE);
 
		if(gameOver) {
			g.setFont(FONT_LARGE);
			String message = new String("Your Score: " + score);
			g.drawString(message, canvas.getWidth() / 2 - (g.getFontMetrics().stringWidth(message) / 2), 250);
 
			g.setFont(FONT_SMALL);
			message = new String("Press Enter to Restart the Game");
			g.drawString(message, canvas.getWidth() / 2 - (g.getFontMetrics().stringWidth(message) / 2), 350);
		} else {
			g.setFont(FONT_SMALL);
			g.drawString("Score:" + score, 10, 20);
		}
	}
 
	public void resetGame() {
		board.resetBoard();
		snake.resetSnake();
		score = 0;
		gameOver = false;
		spawnFruit();
	}
 
	public void spawnFruit() {
		int random = (int)(Math.random() * ((GameBoard.MAP_SIZE * GameBoard.MAP_SIZE) - snake.getSnakeLength())); // if '*' replace by '/' then only one fruit is there for snake
 
		int emptyFound = 0;
		int index = 0;
		while(emptyFound < random) {
			index++;
			if(board.getTile(index % GameBoard.MAP_SIZE, index / GameBoard.MAP_SIZE).equals(TileType.EMPTY)) { // if '/' replaced by '*' then nothing displays on the board 
				emptyFound++;
			}
		}
		board.setTile(index % GameBoard.MAP_SIZE, index / GameBoard.MAP_SIZE, TileType.FRUIT); // it also show nothing when replacing '/' by '/' 
	}
 
 
 
    public void keyPressed(KeyEvent e) {
		if((e.getKeyCode()== KeyEvent.VK_UP)||(e.getKeyCode() == KeyEvent.VK_W)) {
			snake.setDirection(Direction.UP);
		}
		if((e.getKeyCode() == KeyEvent.VK_DOWN)||(e.getKeyCode() == KeyEvent.VK_S)) {
			snake.setDirection(Direction.DOWN);
		}
		if((e.getKeyCode() == KeyEvent.VK_LEFT)||(e.getKeyCode() == KeyEvent.VK_A)) {
			snake.setDirection(Direction.LEFT);
		}
		if((e.getKeyCode() == KeyEvent.VK_RIGHT)||(e.getKeyCode() == KeyEvent.VK_D)) {
			snake.setDirection(Direction.RIGHT);
		}
		if(e.getKeyCode() == KeyEvent.VK_ENTER && gameOver) {
			resetGame();
		}
	}
 
 
 
 
	     public static void main(String[] args)  {
 
                new PlayGame().setVisible(true);
 
		JFrame frame = new JFrame("SnakeGame");
		frame.setDefaultCloseOperation(JFrame.HIDE_ON_CLOSE);
		frame.setResizable(false);
 
		Canvas canvas = new Canvas();
		canvas.setBackground(Color.black);
		canvas.setPreferredSize(new Dimension(GameBoard.MAP_SIZE * GameBoard.TILE_SIZE, GameBoard.MAP_SIZE * GameBoard.TILE_SIZE));
 
		frame.getContentPane().add(canvas);
		frame.pack();
		frame.setLocationRelativeTo(null);
		frame.setVisible(true); 
 
		new Engine(canvas).startGame();
 
 
             }        
}

project is attached within this comment
plz check it