I created a program which should display a spaceship (essentially two rectangles) and shoot a bullet from it every time I press the space button. It doesn't work, though because apparently, my program is passing in a null Ship reference into one of my other classes, the MoveAction class. I have absolutely no clue why it's like this because in my Main class, I instantiate my Ship object before my Shoot class (calling the constructor that uses the ship object). I'm sorry if this question is a little bit silly as I'm still a novice programmer who doesn't have a clue about what he's doing most of the time :) Here's my code:
public enum Direction {
LEFT, RIGHT, SPACE
}
import javax.swing.JFrame;
public class Main {
public static void main(String[] args) {
JFrame frame;
Ship s1;
Shoot shoot;
// Set the frame up
frame = new JFrame();
frame.setSize(400, 300);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setResizable(false);
frame.setVisible(true);
// Get some more necessary objects
s1 = new Ship();
shoot = new Shoot(s1);
frame.getContentPane().add(shoot);
s1.setShoot(shoot);
// Threads
Thread ship = new Thread(s1);
ship.start();
}
}
import java.awt.Graphics;
import java.awt.event.KeyEvent;
import javax.swing.Action;
import javax.swing.ActionMap;
import javax.swing.InputMap;
import javax.swing.JPanel;
import javax.swing.KeyStroke;
public class Shoot extends JPanel {
Ship s1;
public Shoot(Ship s1) {
this.s1 = s1;
addKeyBinding(KeyEvent.VK_LEFT, "left.pressed", new MoveAction(true, s1, Direction.LEFT), true);
addKeyBinding(KeyEvent.VK_LEFT, "left.released", new MoveAction(false, s1, Direction.LEFT), false);
addKeyBinding(KeyEvent.VK_RIGHT, "right.pressed", new MoveAction(true, s1, Direction.RIGHT), true);
addKeyBinding(KeyEvent.VK_RIGHT, "right.released", new MoveAction(false, s1, Direction.RIGHT), false);
addKeyBinding(KeyEvent.VK_SPACE, "space.pressed", new MoveAction(true, s1, Direction.SPACE), true);
addKeyBinding(KeyEvent.VK_SPACE, "space.released", new MoveAction(false, s1, Direction.SPACE), false);
setDoubleBuffered(true);
}
@Override
public void paintComponent(Graphics g) {
// Draw the ship
super.paintComponent(g);
s1.draw(g);
g.fill3DRect(40, 50, 10, 10, false);
}
protected void addKeyBinding(int keyCode, String name, Action action, boolean keyPressed) {
if (keyPressed) {
addKeyBinding(KeyStroke.getKeyStroke(keyCode, 0, false), name, action);
} else {
addKeyBinding(KeyStroke.getKeyStroke(keyCode, 0, true), name, action);
}
}
protected void addKeyBinding(KeyStroke keyStroke, String name, Action action) {
InputMap inputMap = getInputMap(WHEN_IN_FOCUSED_WINDOW);
ActionMap actionMap = getActionMap();
inputMap.put(keyStroke, name);
actionMap.put(name, action);
}
}
import java.awt.Color;
import java.awt.Graphics;
import java.awt.Rectangle;
public class Ship implements Runnable {
int x, y, xDirection, bx, by;
boolean readyToFire, shooting = false;
Rectangle bullet;
Shoot shoot;
public Ship() {
x = 175;
y = 275;
bullet = new Rectangle(0, 0, 3, 5);
}
public void draw(Graphics g) {
// System.out.println("draw() called");
g.setColor(Color.BLUE);
g.fillRect(x, y, 40, 10);
g.fillRect(x + 18, y - 7, 4, 7);
if (shooting) {
g.setColor(Color.RED);
g.fillRect(bullet.x, bullet.y, bullet.width, bullet.height);
}
shoot.repaint();
}
public void move() {
x += xDirection;
if (x <= 0)
x = 0;
if (x >= 360)
x = 360;
shoot.repaint();
}
public void shoot() {
if (shooting) {
bullet.y--;
shoot.repaint();
}
}
public void setXDirection(int xdir) {
xDirection = xdir;
}
public void setShoot(Shoot shoot) {
this.shoot = shoot;
}
@Override
public void run() {
try {
while (true) {
shoot();
move();
Thread.sleep(5);
}
} catch (Exception e) {
System.err.println(e.getMessage());
}
}
}
import java.awt.Rectangle;
import java.awt.event.ActionEvent;
import java.util.HashSet;
import javax.swing.AbstractAction;
public class MoveAction extends AbstractAction {
boolean pressed;
Ship s1;
Direction dir;
private HashSet<Direction> movement;
public MoveAction(boolean pressed, Ship s1, Direction dir) {
System.out.println("moveaction class");
this.pressed = pressed;
this.s1 = s1;
this.dir = dir;
}
@Override
public void actionPerformed(ActionEvent e) {
try {
if (movement.contains(Direction.LEFT)) {
if (pressed) {
s1.setXDirection(-1);
} else {
s1.setXDirection(0);
}
} else if (movement.contains(Direction.RIGHT)) {
if (pressed) {
s1.setXDirection(1);
} else {
s1.setXDirection(0);
}
} else if (movement.contains(Direction.SPACE)) {
if (pressed) {
if (s1.bullet == null)
s1.readyToFire = true;
if (s1.readyToFire) {
s1.bullet.x = s1.x + 18;
s1.bullet.y = s1.y - 7;
s1.shooting = true;
}
} else {
s1.readyToFire = false;
if (s1.bullet.y <= -7) {
s1.bullet = null;
s1.shooting = false;
s1.bullet = null;
s1.bullet = new Rectangle(0, 0, 0, 0);
s1.readyToFire = true;
}
}
}
} catch (NullPointerException ex) {
System.out.println("NullPointerException");
}
}
Stack Trace :)
at MoveAction.actionPerformed(MoveAction.java:24)
at javax.swing.SwingUtilities.notifyAction(Unknown Source)
at javax.swing.JComponent.processKeyBinding(Unknown Source)
at javax.swing.KeyboardManager.fireBinding(Unknown Source)
at javax.swing.KeyboardManager.fireKeyboardAction(Unknown Source)
at javax.swing.JComponent.processKeyBindingsForAllComponents(Unknown Source)
at javax.swing.SwingUtilities.processKeyBindings(Unknown Source)
at javax.swing.UIManager$2.postProcessKeyEvent(Unknown Source)
at java.awt.DefaultKeyboardFocusManager.dispatchKeyEvent(Unknown Source)
at java.awt.DefaultKeyboardFocusManager.preDispatchKeyEvent(Unknown Source)
at java.awt.DefaultKeyboardFocusManager.typeAheadAssertions(Unknown Source)
at java.awt.DefaultKeyboardFocusManager.dispatchEvent(Unknown Source)
at java.awt.Component.dispatchEventImpl(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Window.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
at java.awt.EventQueue.access$500(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source)
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source)
at java.awt.EventQueue$4.run(Unknown Source)
at java.awt.EventQueue$4.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source)
at java.awt.EventQueue.dispatchEvent(Unknown Source)
at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.run(Unknown Source)
You never initialize your member variable HashSet<Direction> movement, that's why you always get a NPE.
Try this
private Set<Direction> movement = new HashSet<>();
By the way, declaring an implementation class HashSet as a variable type is a bad practice. You should use an interface Set instead.