pressing 2 keys on the keyboard at the same time?

Working demo (altered for this thread). 2 classes, just save into the one java file as BufferStrat.java...

this is probably not the best way to do keylistener but it works very nicely for me. you'd possibly want to extend that array and make it track every key on the keyboard but i don't plan to let my users change their key config for now...

here, it's used in the render() method though for most purposes you'd put it somewhere else.

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import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.awt.image.BufferStrategy; 
 
 
public class BufferStrat 
{ 
      final int SPEED = 10;
      JFrame mainFrame; 
      BufferStrategy bufferStrategy; 
      int ScreenWidth; 
      int ScreenHeight; 
      boolean Running = true; 
      JPanel cp;
      int n = 0;
      int buffers = 2;
      long oldTime;
      long newTime;
      int ticks = 0;
      int lastTicks = 0;
      XKListener keys = new XKListener();
      public BufferStrat() 
      {
            //------
            GraphicsEnvironment ge = GraphicsEnvironment.getLocalGraphicsEnvironment(); 
            GraphicsDevice gd = ge.getDefaultScreenDevice(); 
            GraphicsConfiguration gc = gd.getDefaultConfiguration(); 
            mainFrame = new JFrame(gc);
            cp = (JPanel)mainFrame.getContentPane();
            cp.setLayout(null);
            mainFrame.setIgnoreRepaint(true);
            mainFrame.setResizable(false);
            ScreenWidth = 520;
            ScreenHeight = 568;
            mainFrame.setSize(new Dimension(ScreenWidth, ScreenHeight)); 
            mainFrame.show();
            mainFrame.createBufferStrategy( 2 );
            bufferStrategy = mainFrame.getBufferStrategy();
            
            long oldTime = System.currentTimeMillis();
            
            //*****
            mainFrame.addKeyListener(keys);
            mainFrame.addWindowListener(new WindowAdapter() {
                  public void windowClosing(WindowEvent e) {
                        System.exit(0);
                  }
            });
            GT.start();
      }
      
      public void go()
      {
            //do game loop stuff here... i.e if left is pressed, move dude left.
            //would be if(keys.keyStates[2])
            // sprite.moveLeft() (or something)
            render();
      }
      int i = 0;
      private void render() 
      { 
            if( !bufferStrategy.contentsLost() ) 
            { 
                  Graphics g = bufferStrategy.getDrawGraphics(); 
                  
                  // Clear the drawing buffer to white 
                  g.setColor( Color.white ); 
                  g.fillRect( 0, 0, ScreenWidth, ScreenHeight ); 
                  
                  g.setColor(Color.blue);
                  g.drawString("Use the arrow keys", 150, 200);
                  
                  if(keys.keyStates[0])
                  g.fillRect( 250, 250, 40, 40 );
                  else g.drawRect( 250, 250, 40, 40 ); 
                  if(keys.keyStates[1])
                  g.fillRect( 250, 300, 40, 40 );
                  else g.drawRect( 250, 300, 40, 40 ); 
                  if(keys.keyStates[2])
                  g.fillRect( 200, 300, 40, 40 );
                  else g.drawRect( 200, 300, 40, 40 ); 
                  if(keys.keyStates[3])
                  g.fillRect( 300, 300, 40, 40 );
                  else g.drawRect( 300, 300, 40, 40 ); 
                  
                  
                  bufferStrategy.show(); 
                  g.dispose(); 
            } 
      }
      public static void main( String[] args ) 
      { 
            BufferStrat test = new BufferStrat(); 
      } 
      ///timer
      ActionListener clickLsn = new ActionListener()
            {
                  public void actionPerformed(ActionEvent e)
                  {
                        go();
                  }
            };
      Timer GT = new Timer(SPEED, clickLsn);
} 


class XKListener implements KeyListener
{
      public boolean keyStates[] = new boolean[4];
      //cause we are checking 4 keys... you probably want more.
      int keyCode;
      char c;
      public XKListener()
      {
            //initialise all the keys as not pressed.
            for (int i=0; i<keyStates.length; i++)
            keyStates[i] = false;
      }
      // Handle the key typed event. does nothing.
      //this is how you would have been previously doing it
      public void keyTyped(KeyEvent e){}

      /** Handle the key pressed event. */
      public void keyPressed(KeyEvent e)
      {
            setBoolean(e, true);
      }

      /** Handle the key released event. */
      public void keyReleased(KeyEvent e)
      {
            setBoolean(e, false);
      }
      
      protected void setBoolean(KeyEvent e, boolean isPressed)
      {
            c = e.getKeyChar();
            keyCode = e.getKeyCode();
            switch (keyCode)
            {
            case (KeyEvent.VK_UP):
            keyStates[0] = isPressed;
            break;
            case (KeyEvent.VK_DOWN):
            keyStates[1] = isPressed;
            break;
            case (KeyEvent.VK_LEFT):
            keyStates[2] = isPressed;
            break;
            case (KeyEvent.VK_RIGHT):
            keyStates[3] = isPressed;
            break;
            default:
            System.out.println("Not using that key");
            }
      }
}

it's a bit long cause it's part of another demo that i used ... so you also have a double buffering demo here as well if you need it, tho it's shown off doing more flashy stuff in another thread here.