Increment and Decrement time with keys:

[xterradaniel]

Just a heads up, I posted this same question on Dream in code over 2 hours ago and nobody has answered. The link is http://www.dreamincode.net/forums/topic/197275-checking-for-multiple-keys-pressed/page__p__1153044__fromsearch__1&#entry1153044

I have been trying to figure out how to increment or decrement a value if two keys are pressed at the same time (ctrl+, ctrl-). I cant seem to get it working. If you can lead me to an elementary example or give me some pointers I would appreciate it.

I am trying to make a race car, built from simple shapes, speed up and slow down when ctrl+ or ctrl- is pressed.

The part in red is what I was attempting.

Everything else works except that.
Code:

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class Exercise16_15 extends JFrame {

    public Exercise16_15() {
        add(new raceCar());

    }

    class raceCar extends JPanel {

        protected int xCordinate = 0;
        protected int yCordinate = 150;
        protected int z = 300;

        public raceCar() {
            int o = 0;
            Timer timer = new Timer((200 + g), new ActionListener() {

                public void actionPerformed(ActionEvent e) {
                    xCordinate += 10;

                    repaint();
                }
            });
            timer.start();



        }
        private boolean locked = false;
        private int twoPressed;
        protected int g = 0;

        public raceCar(int o) {


            addKeyListener(new KeyAdapter() {

                @Override
                public void keyPressed(KeyEvent e) {
                    if (locked) {


                        switch (e.getKeyCode()) {
                            case KeyEvent.VK_PLUS:
                                g = -10000;
                                locked = true;
                                twoPressed = KeyEvent.VK_PLUS;
                                break;
                            case KeyEvent.VK_MINUS:
                                g = 10;
                                locked = true;
                                twoPressed = KeyEvent.VK_PLUS;
                                break;
                            case KeyEvent.VK_CONTROL:
                                locked = true;
                                twoPressed = KeyEvent.VK_CONTROL;
                                break;
                            default:
                        }
                    }

                }

                public void keyUp(KeyEvent e) {
                    if (e.getKeyCode() == twoPressed) {
                        locked = false;
                    }
                }
            });

        }

        @Override
        public void paintComponent(Graphics g) {
            super.paintComponent(g);

            yCordinate = getHeight();
            z = getWidth();
            g.setColor(Color.WHITE);
            g.fillRect(0, 0, z, yCordinate);
            Polygon raceCarParts = new Polygon();
            raceCarParts.addPoint(xCordinate + 10, yCordinate - 20);
            raceCarParts.addPoint(xCordinate + 20, yCordinate - 30);
            raceCarParts.addPoint(xCordinate + 30, yCordinate - 30);
            raceCarParts.addPoint(xCordinate + 40, yCordinate - 20);




            if (xCordinate < z - 40) {
                g.setColor(Color.BLACK);
                g.fillOval(xCordinate + 10, yCordinate - 11, 10, 10);
                g.fillOval(xCordinate + 30, yCordinate - 11, 10, 10);
                g.setColor(Color.BLUE);
                g.fillRect(xCordinate, yCordinate - 20, 50, 10);
                g.setColor(Color.GREEN);
                g.fillPolygon(raceCarParts);
                g.setColor(Color.GREEN);


            } else {
                xCordinate = 0;


            }
        }
    }

    public static void main(String[] args) {
        Exercise16_15 frame = new Exercise16_15();
        frame.setTitle("Race Car");
        frame.setSize(300, 150);
        frame.setLocationRelativeTo(null);
        frame.setDefaultCloseOperation(EXIT_ON_CLOSE);
        frame.setVisible(true);

    }
}

[Taywin]

The idea is to have a ctrl flag in your class. When a key press is a ctrl button, change the flag to true. When the key up is ctrl, change it back to false. Therefore, you could now check whether or not the ctrl is being held.

In your current implementation, you have the flag works on all designated keys; as a result, it will never get inside the if(locked) because it will never be true in the first place. Besides when you press another key the second time, it overwrites your existing value.

public void keyPressed(KeyEvent e) {
  if (locked) {  // ctrl key is being held
    switch (e.getKeyCode()) {
      case KeyEvent.VK_PLUS:
        g = -10000;
        break;
      case KeyEvent.VK_MINUS:
        g = 10;
        break;
      default:
    }
  }
  else {  // ctrl button is not being pressed
    if(e.getKeyCode() == KeyEvent.VK_CONTROL) {
      locked = true;
    }
  }
}

public void keyUp(KeyEvent e) {
  if (e.getKeyCode() == KeyEvent.VK_CONTROL) {  // release ctrl
    locked = false;
  }
}