Thread: JPanel not reacting to Keystrokes

I'm working on a tetris game and I've been trying to get the keystroke actions to work; i've done it before in other applications but for some reason my jpanel is not calling any of the key methods when i hit a key. I don't know if this is a problem with the focus, whether I left out some needed code, or something else altogether... please help!

The only code i need help on is PlayPanel (and possibly MainFrame) but I provided all my code for those who wish to compile and run it

EDIT: I have also been looking at KeyBindings, does anyone know if that would help in a situation like this?

MainFrame:

package Tetris;
 
import java.awt.*;
import javax.swing.*;
 
@SuppressWarnings({ "serial" })
public class MainFrame extends JFrame {
	public MainFrame() {
		super("Tetris");
		setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		setResizable(false);
		JPanel optionInfo = new JPanel();
		optionInfo.setLayout(new BoxLayout(optionInfo, BoxLayout.Y_AXIS));
		optionInfo.setBackground(Color.BLACK);
		PlayPanel play = new PlayPanel();
		InfoPanel info = new InfoPanel(play);
		OptionPanel options = new OptionPanel(info, play);
		optionInfo.add(options);
		optionInfo.add(info);
		add(play, BorderLayout.CENTER);
		add(optionInfo, BorderLayout.EAST);
		pack();
		setVisible(true);
	}
	public static void main(String[] args) {
		new MainFrame();
	}
}

PlayPanel:

package Tetris;
 
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.border.Border;
import java.util.TimerTask;
import java.util.Timer;
 
@SuppressWarnings({ "serial", "unused" })
public class PlayPanel extends JPanel implements KeyListener {
	private Tetromino tet;
	private Timer dropTimer;
	private Timer colorTimer;
	private JButton[][] buttonAt;
	private boolean[][] isDeadButtonAt;
	private int linesCleared = 0;
	private int dropSpeed = 1000;
 
	public PlayPanel() {
		super();
		setBackground(Color.BLACK);
		GridLayout grid = new GridLayout(18, 10); //rows, columns
		setLayout(grid);
		buttonAt = new JButton[10][18];
		isDeadButtonAt = new boolean[10][18];
		for(int y = 0; y < 18; y++) {
			for(int x = 0; x < 10; x++) {
				buttonAt[x][y] = new JButton();
				buttonAt[x][y].setEnabled(false);
				buttonAt[x][y].setPreferredSize(new Dimension(30, 30));
				buttonAt[x][y].setOpaque(false); //false makes background visible
				add(buttonAt[x][y]);
			}
		}
		setFocusable(true);
		addKeyListener(this);
		setVisible(true);
	}
	public void newGame() {
		if(!(dropTimer == null)) { dropTimer.cancel(); }
		if(!(colorTimer == null)) { colorTimer.cancel(); }
		for(int x = 0; x < 10; x++) {
			for(int y = 0; y < 18; y++) {
				buttonAt[x][y].setBackground(null);
				buttonAt[x][y].setOpaque(false);
				isDeadButtonAt[x][y] = false;
			}
		}
		dropSpeed = 1000;
		dropTimer  = new Timer();
		dropTimer.schedule(new DropTimer(), dropSpeed, dropSpeed);
		colorTimer = new Timer();
		colorTimer.schedule(new ColorTimer(), 0, 100);
		tet = new Tetromino();
	}
	public void moveTet(boolean rotated) {
		int[] x = new int[4];	int lastX[] = new int[4];
		int[] y = new int[4];	int lastY[] = new int[4];
		int dropLevel = tet.getDropLevel();
		int lastDropLevel = tet.getLastDropLevel();
		int rotation = tet.getRotation();
		int height = tet.getHeight();
		int movedPos = tet.getMovedPos();
		if(movedPos < 0 || movedPos > 9) { return; }
		for(int i = 0; i < 4; i++) {
			x[i] = tet.getPosX()[rotation][i] + movedPos;
			y[i] = tet.getPosY()[rotation][i] + dropLevel;
			lastX[i] = tet.getLastPosX()[i] + movedPos;
			lastY[i] = tet.getLastPosY()[i] + lastDropLevel;
			if(dropLevel + height > 18 || isDeadButtonAt[x[i]][y[i]]) {
				if(rotated == true) { return; }
				movedPos = 0;
				setDeadButtons();
				tet = new Tetromino();
				return;
			}
		}
		for(int i = 0; i < 4; i++) {
			buttonAt[lastX[i]][lastY[i]].setOpaque(false);
			buttonAt[lastX[i]][lastY[i]].setBackground(null);
		}
		for(int i = 0; i < 4; i++) {
			buttonAt[x[i]][y[i]].setOpaque(true);
			buttonAt[x[i]][y[i]].setBackground(tet.getNewColor());	
		}
		tet.setLastPos(tet.getPosX()[rotation], tet.getPosY()[rotation]);
		if(rotated == false) {
			tet.setLastDropLevel(dropLevel);
			tet.setDropLevel(dropLevel + 1);
		}
	}
	public void setDeadButtons() {
		for(int x = 0; x < 10; x++) {
			for(int y = 0; y < 18; y++) {
				if(buttonAt[x][y].isOpaque()) { isDeadButtonAt[x][y] = true; }
				else { isDeadButtonAt[x][y] = false; }
			}
		}
	}
	public void keyTyped(KeyEvent e) { }
	public void keyReleased(KeyEvent e) { }
	public void keyPressed(KeyEvent e) {
		System.out.println("KEY PRESSED");
		switch(e.getKeyCode()) {
		case KeyEvent.VK_UP:
			System.out.println("UP PRESSED");
			tet.rotate();
			moveTet(true);
			break;
		case KeyEvent.VK_LEFT:
			System.out.println("LEFT PRESSED");
			tet.setMovedPos(tet.getMovedPos() - 1);
			moveTet(false);
			break;
		}
	}
	public void pause() {
		dropTimer.cancel();
		//colorTimer.cancel();
	}
	public void resume() {
		dropTimer = new Timer();
		//colorTimer = new Timer();
		dropTimer.schedule(new DropTimer(), dropSpeed, dropSpeed);
		//colorTimer.schedule(new ColorTimer(), 0, 100);
	}
	public class DropTimer extends TimerTask implements Runnable {
		public void run() {
			moveTet(false);
		}
	}
	public class ColorTimer extends TimerTask implements Runnable {
		public void run() {
			for(int x = 0; x < 10; x++) {
				for(int y = 0; y < 18; y++) {
					if(buttonAt[x][y].isOpaque()) {
						buttonAt[x][y].setBackground(tet.getNewColor());
					}
				}
			}
		}
	}
	public int getLinesCleared() {
		return linesCleared;
	}
	public void resetLinesCleared() {
		linesCleared = 0;
	}
	public void updateLinesCleared() {
 
	}
}

Tetromino:

package Tetris;
 
import java.util.Random;
import java.awt.Color;
 
public class Tetromino {
	private int type;
	private Color tetColor;
	private int[] lastPosX = new int[]{0, 0, 0, 0};
	private int[] lastPosY = new int[]{0, 0, 0, 0};
	private int[][] posX = new int[4][4];
	private int[][] posY = new int[4][4];
	private int height;
	private int movedPos = 5; //middle of grid layout
	private int dropLevel = 0;
	private int lastDropLevel = 0;
	private int rotation = 0;
	private int lastRotation = -1;
 
	public Tetromino() {
		Random genNum = new Random();
		type = genNum.nextInt(7);
		switch(type) {
		case 0: buildIBlock(); break;
		case 1: buildOBlock(); break;
		case 2: buildTBlock(); break;
		case 3: buildLBlock(); break;
		case 4: buildJBlock(); break;
		case 5: buildSBlock(); break;
		case 6: buildZBlock(); break;
		} 
		if(type == 0) { height = 1;	}
		else { height = 2; }
		tetColor = getNewColor();
	}
	public Color getNewColor() {
		Color newColor = null;
		Random genNum = new Random();
		int colorType = genNum.nextInt(7);
		switch(colorType) {
		case 0: newColor = Color.BLUE; break;
		case 1: newColor = Color.CYAN; break;
		case 2: newColor = Color.GREEN; break;
		case 3: newColor = Color.MAGENTA; break;
		case 4: newColor = Color.ORANGE; break;
		case 5: newColor = Color.RED; break;
		case 6: newColor = Color.WHITE; break;
		}
		if(newColor.equals(tetColor)) { getNewColor(); }
		return newColor;
	}
	public void buildIBlock() {
		for(int i = 0; i < 4; i++) {
			if(i%2 == 0) {
				posX[i] = new int[] {-2, -1, 0, 1};		posY[i] = new int[] {0, 0, 0, 0};
			}
			else {
				posX[i] = new int[] {0, 0, 0, 0};		posY[i] = new int[] {0, 1, 2, 3};
			}
		}
	}	
	public void buildOBlock() {
		for(int i = 0; i < 4; i++) {
			posX[i] = new int[] {-1, 0, -1, 0};		posY[i] = new int[] {0, 0, 1, 1};
		}
	}
	public void buildTBlock() {
		posX[0] = new int[] {-1, 0, 1, 0};		posY[0] = new int[] {0, 0, 0, 1};
		posX[1] = new int[] {0, -1, 0, 0};		posY[1] = new int[] {0, 1, 1, 2};
		posX[2] = new int[] {0, -1, 0, 1};		posY[2] = new int[] {0, 1, 1, 1};
		posX[3] = new int[] {-1, -1, 0, -1};	posY[3] = new int[] {0, 1, 1, 2};
	}
	public void buildLBlock() {
		posX[0] = new int[] {-1, 0, 1, -1};		posY[0] = new int[] {0, 0, 0, 1};
		posX[1] = new int[] {-1, 0, 0, 0}; 		posY[1] = new int[] {0, 0, 1, 2};
		posX[2] = new int[] {1, -1, 0, 1};		posY[2] = new int[] {0, 1, 1, 1};
		posX[3] = new int[] {-1, -1, -1, 0};	posY[3] = new int[] {0, 1, 2, 2};
	}	
	public void buildJBlock() {
		posX[0] = new int[] {-1, 0, 1, 1};		posY[0] = new int[] {0, 0, 0, 1};
		posX[1] = new int[] {0, 0, -1, 0};		posY[1] = new int[] {0, 1, 2, 2};
		posX[2] = new int[] {-1, -1, 0, 1};		posY[2] = new int[] {0, 1, 1, 1};
		posX[3] = new int[] {-1, 0, -1, -1};	posY[3] = new int[] {0, 0, 1, 2};
	}	
	public void buildSBlock() {
		for(int i = 0; i < 4; i++) {
			if(i%2 == 0) {
				posX[i] = new int[] {0, 1, -1, 0};		posY[i] = new int[] {0, 0, 1, 1};
			} else {
				posX[i] = new int[] {-1, -1, 0, 0};		posY[i] = new int[] {0, 1, 1, 2};
			}
		}
	}
	public void buildZBlock() {
		for(int i = 0; i < 4; i++) {
			if(i%2 == 0) {
				posX[i] = new int[] {-1, 0, 0, 1};		posY[i] = new int[] {0, 0, 1, 1};
			} else {
				posX[i] = new int[] {0, 0, -1, -1};		posY[i] = new int[] {0, 1, 1, 2};
			}
		}
	}
	public void rotate() {
		lastRotation = rotation;
		rotation = (rotation+1)%4;
		switch(type) {
		case 0: if(rotation % 2 == 0) { height = 1; } else { height = 4; } break;
		case 1: height = 2; break;
		default: if(rotation % 2 == 0) { height = 2; } else { height = 3; } break;
		}
	}
	public void setLastPos(int[] posX, int[] posY) {
		lastPosX = posX;	lastPosY = posY;
	}
	public void resetLastPos() {
		lastPosX = new int[] {0,0,0,0};
		lastPosY = new int[] {0,0,0,0};
		lastDropLevel = 0;
	}
	public int getType() { return type; }
	public int[] getLastPosX() { return lastPosX; }
	public int[] getLastPosY() { return lastPosY; }
	public int[][] getPosX() { return posX; }
	public int[][] getPosY() { return posY; }
	public int getHeight() { return height; }
	public int getMovedPos() { return movedPos; }
	public int getDropLevel() { return dropLevel; }
	public int getLastDropLevel() { return lastDropLevel; }
	public int getLastRotation() { return lastRotation; }
	public int getRotation() { return rotation; }
	public Color getTetColor() { return tetColor; }
	public void setMovedPos(int m) { movedPos = m; }
	public void setDropLevel(int d) { dropLevel = d; }
	public void setLastDropLevel(int l) { lastDropLevel = l; }
}

InfoPanel:

package Tetris;
 
import java.awt.*;
 
import javax.swing.*;
 
@SuppressWarnings({ "serial" })
public class InfoPanel extends JPanel  {
	private ScoreTracker scoreTracker;
	private PlayPanel playPanel;
	private JLabel score = new JLabel();
	private JLabel level = new JLabel();
	private JLabel linesCleared = new JLabel();
 
	public InfoPanel(PlayPanel play) {
		playPanel = play;
		scoreTracker = new ScoreTracker();
		setOpaque(false);
		setBorder(BorderFactory.createEmptyBorder(10, 0, 0, 0));
		setLayout(new BoxLayout(this, BoxLayout.Y_AXIS));
		JLabel scoreLabel = new JLabel("SCORE");
		JLabel levelLabel = new JLabel("LEVEL");
		JLabel linesLabel = new JLabel("LINES");
		JLabel clearedLabel = new JLabel("CLEARED");
		scoreLabel.setForeground(Color.WHITE);
		levelLabel.setForeground(Color.WHITE);
		linesLabel.setForeground(Color.WHITE);
		clearedLabel.setForeground(Color.WHITE);
		score.setForeground(Color.WHITE);
		level.setForeground(Color.WHITE);
		linesCleared.setForeground(Color.WHITE);
		scoreLabel.setAlignmentX(Component.CENTER_ALIGNMENT);
		levelLabel.setAlignmentX(Component.CENTER_ALIGNMENT);
		linesLabel.setAlignmentX(Component.CENTER_ALIGNMENT);
		clearedLabel.setAlignmentX(Component.CENTER_ALIGNMENT);
		score.setAlignmentX(Component.CENTER_ALIGNMENT);
		level.setAlignmentX(Component.CENTER_ALIGNMENT);
		linesCleared.setAlignmentX(Component.CENTER_ALIGNMENT);
		add(scoreLabel);
		add(score);
		add(levelLabel);
		add(level);
		add(linesLabel);
		add(clearedLabel);
		add(linesCleared);
		setVisible(true);	
	}
	public void paintComponent(Graphics g) {
		super.paintComponent(g);
		score.setText("" + scoreTracker.getScore());
		level.setText("" + (1 + Integer.parseInt(score.getText())/1000));
		linesCleared.setText("" + playPanel.getLinesCleared());
	}
	public void updateInfo() {
		if(scoreTracker == null) scoreTracker = new ScoreTracker();
		else scoreTracker.updateScore();
		repaint();
	}
	public void resetInfo() {
		scoreTracker.resetScore();
		playPanel.resetLinesCleared();
		repaint();
	}
}

OptionPanel:

package Tetris;
 
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.border.*;
 
@SuppressWarnings({ "serial", "unused" })
public class OptionPanel extends JPanel implements ActionListener {
	private InfoPanel infoPanel;
	private PlayPanel playPanel;
	private JButton newGame = new JButton("NEW GAME");
	private JButton pause = new JButton("PAUSE");
	private JButton quit = new JButton("QUIT");
	private JButton addScore = new JButton("+100");
	private Font f = new Font("SERIF", 0, 14);
	private boolean isPaused;
 
 
	public OptionPanel(InfoPanel info, PlayPanel play) {
		infoPanel = info;
		playPanel = play;
		setOpaque(false);
		setLayout(new BoxLayout(this, BoxLayout.Y_AXIS));
		setBorder(BorderFactory.createEmptyBorder(10, 10, 10, 10));
		newGame.addActionListener(this);
		pause.addActionListener(this);
		quit.addActionListener(this);
		addScore.addActionListener(this);
		newGame.setFont(f);
		newGame.setForeground(Color.GREEN);
		newGame.setBackground(Color.BLACK);
		newGame.setBorder(null);
		newGame.setAlignmentX(Component.CENTER_ALIGNMENT);
		pause.setFont(f);
		pause.setForeground(Color.ORANGE);
		pause.setBackground(Color.BLACK);
		pause.setBorder(null);
		pause.setAlignmentX(Component.CENTER_ALIGNMENT);
		quit.setFont(f);
		quit.setForeground(Color.RED);
		quit.setBackground(Color.BLACK);
		quit.setBorder(null);
		quit.setAlignmentX(Component.CENTER_ALIGNMENT);
		add(newGame);
		add(pause);
		add(quit);
		setVisible(true);
	}
	public void actionPerformed(ActionEvent event) {
		Object source = event.getSource();
		if(source.equals(newGame)) {
			pause.setText("PAUSE");
			infoPanel.resetInfo();
			playPanel.newGame();
		}
		if(source.equals(pause)) {
			if(pause.getText().equals("PAUSE")) { 
				pause.setText("RESUME");
				playPanel.pause();
				}
			else { 
				pause.setText("PAUSE"); 
				playPanel.resume();
			}
		}
		if(source.equals(quit)) {
			System.exit(0);
		}
		if(source.equals(addScore)) {
			infoPanel.updateInfo();
		}
	}
}

ScoreTracker (necessary to compile but I haven't fleshed out the methods yet)

package Tetris;
 
public class ScoreTracker {
	private int score;
 
	public ScoreTracker() {
		score = 0;
	}	
	public void updateScore() {
		score += 100;
	}	
	public void resetScore() {
		score = 0;
	}	
	public int getScore() {
		return score;
	}
}

Originally Posted by sonicjr

I'm working on a tetris game and I've been trying to get the keystroke actions to work; i've done it before in other applications but for some reason my jpanel is not calling any of the key methods when i hit a key. I don't know if this is a problem with the focus, whether I left out some needed code, or something else altogether... please help!

Usually yes, this is a problem of focus.

The only code i need help on is PlayPanel (and possibly MainFrame) but I provided all my code for those who wish to compile and run it

EDIT: I have also been looking at KeyBindings, does anyone know if that would help in a situation like this?

And yes, Key Bindings will usually solve this issue. Regardless, you are encouraged to use Key Bindings in place of KeyListeners as a general rule since the latter are felt to be a much lower-level construct.

Addendum: don't use a java.util.Timer with Swing GUI's, especially for code that needs to be called on the event thread. This is what javax.swing.Timer's are for. Use them instead.

Addendum 2: For a small taste of Key Binding, change your PlayPanel constructor to something like:

   public PlayPanel() {
      super();
      setBackground(Color.BLACK);
      GridLayout grid = new GridLayout(18, 10); // rows, columns
      setLayout(grid);
      buttonAt = new JButton[10][18];
      isDeadButtonAt = new boolean[10][18];
      for (int y = 0; y < 18; y++) {
         for (int x = 0; x < 10; x++) {
            buttonAt[x][y] = new JButton();
            buttonAt[x][y].setEnabled(false);
            buttonAt[x][y].setPreferredSize(new Dimension(30, 30));
            buttonAt[x][y].setOpaque(false); // false makes background visible
            add(buttonAt[x][y]);
         }
      }
      setFocusable(true);
      // addKeyListener(this); // you don't need this
      // setVisible(true); // you rarely need this in a non-top level window
 
      ActionMap actionMap = getActionMap();
      int condition = WHEN_IN_FOCUSED_WINDOW;
      InputMap inputMap = getInputMap(condition);
 
      String upKey  = "up key";
      inputMap.put(KeyStroke.getKeyStroke(KeyEvent.VK_UP, 0), upKey);
      actionMap.put(upKey, new AbstractAction() {
 
         @Override
         public void actionPerformed(ActionEvent aEvt) {
            System.out.println("up key pressed");
         }
      });
   }