Help regarding a java game

[robertpas]

Hello,

This is my first post on Java Forums and I really need help. I have made a small java game using Eclipse, but i have a problem. It randomly doesn't start.
When I hit run it either works as expected or the game freezes.

When that happens i get these errors

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at Game.Board.checkCollisions(Board.java:92)
at Game.Board.actionPerformed(Board.java:44)
at javax.swing.Timer.fireActionPerformed(Timer.java:3 13)
at javax.swing.Timer$DoPostEvent.run(Timer.java:244)
at java.awt.event.InvocationEvent.dispatch(Invocation Event.java:226)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.j ava:647)
at java.awt.EventQueue.access$000(EventQueue.java:96)
at java.awt.EventQueue$1.run(EventQueue.java:608)
at java.awt.EventQueue$1.run(EventQueue.java:606)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.AccessControlContext$1.doIntersectio nPrivilege(AccessControlContext.java:105)
at java.awt.EventQueue.dispatchEvent(EventQueue.java: 617)
at java.awt.EventDispatchThread.pumpOneEventForFilter s(EventDispatchThread.java:275)
at java.awt.EventDispatchThread.pumpEventsForFilter(E ventDispatchThread.java:200)
at java.awt.EventDispatchThread.pumpEventsForHierarch y(EventDispatchThread.java:190)
at java.awt.EventDispatchThread.pumpEvents(EventDispa tchThread.java:185)
at java.awt.EventDispatchThread.pumpEvents(EventDispa tchThread.java:177)
at java.awt.EventDispatchThread.run(EventDispatchThre ad.java:138)

What is the cause of all this?


I am aware that my style of programming is a bit sloppy, but I am new to java and don't know how to write a program efficiently.

Help please

[sunde887]

Is it a lot of code? If not, please post it here and wrap it in code tags ([code] YOUR CODE HERE [/code])

Generally a NullPointerException means something hasn't been initialized before being called. Follow the line numbers from the stack trace and make sure everything is correctly initialized (i.e not null). Don't be afraid to use print statements to find the value of objects.

[Fubarable]

First you need to inspect the line that's throwing the NPE (null pointer exception) and check to see which variable is null on that line. Next trace back through your program to see why it's null.

[robertpas]

ok, so here's where Eclipse has problems

 
public void checkCollisions()
	{
		Rectangle r1=en.getBounds();

getBounds is defined as

 public Rectangle getBounds()
    {
    	return new Rectangle(x,y,184,147);
    }

Here's the whole Board class:

package Game;

import java.awt.*;
import java.awt.event.*;

import javax.swing.*;

public class Board extends JPanel implements ActionListener, Runnable{
	Dude p;
	Image img;
	Timer time;
	int v = 600;
	
	int ok=0;
    Thread animator;
    
    Enemy en;
    Enemy en2;
    Enemy en3,en5;
    Enemy2 en4,en6,healthpack;
    Platform p1;
    boolean lost=false;
    
    boolean k=false;
	public Board(){
		p=new Dude();
		addKeyListener(new AL());
		setFocusable(true);
		ImageIcon i =new ImageIcon("Background.jpg");
		img=i.getImage();
		time= new Timer(5, this);
		time.start();
		p1=new Platform(550,430,"platform.png");
		en=new Enemy(1400,550,"enemy.png");
		en2=new Enemy(-197,550,"enemy.png");
		en3=new Enemy(880,280,"enemy.png");
		en4=new Enemy2(298,280,"enemy.png");
		en5=new Enemy(1400,50,"fighter-jet.png");
		en6=new Enemy2(-197,50,"fighter-jet2.png");
		healthpack=new Enemy2(633,650,"toolbox.png");
		
	}
	public void actionPerformed(ActionEvent e){
	checkCollisions();

		p.move();
		
	     en.move(3);
		 en2.move(-3);
		if (en3.x>=300)
		    en3.move(3);
		else if(en3.x<=300){
			
			en3.isAlive=false;
			en4.isAlive=true;
			en4.move(-3);
			
			if(en4.x>=880)
			{
				en4.x=298;
				en4.isAlive=false;
			    en3.isAlive=true;
			    en3.x=880;
			    en3.move(3);
			}
		}
		if (en5.x>=-197)
		    en5.move(6);
		else if(en5.x<=-197){
			
			en5.isAlive=false;
			en6.isAlive=true;
			en6.move(-6);
			
			if(en6.x>=1400)
			{
				en6.x=-197;
				en6.isAlive=false;
			    en5.isAlive=true;
			    en5.x=1400;
			    en5.move(3);
			}
		}
	
		if(p.score>1999 && p.score%1000==0)
			healthpack.isAlive=true;
		repaint();
	}
	
	public void checkCollisions()
	{
		Rectangle r1=en.getBounds();
		Rectangle r2=en2.getBounds();
		Rectangle r3=p1.getBounds();
		Rectangle r4=en3.getBounds();
		Rectangle r5=en4.getBounds();
		Rectangle r6=en5.getBounds();
		Rectangle r7=en6.getBounds();
		Rectangle h=healthpack.getBounds();
		Rectangle d=p.getBounds();
		if(d.intersects(r1)||d.intersects(r2))
		{
			if(v>=en.y-100)
			  p.hp=p.hp-1;
			if (p.hp==0)
			  lost=true;
			if(p.hp<0)
				p.hp=0;
		}
		if(d.intersects(h)&& healthpack.Alive()==true)
		{
			p.hp=p.hp+25;
			if(p.hp>100)
				p.hp=100;
			healthpack.isAlive=false;
		}
		if((d.intersects(r4)&& en3.isAlive==true)||(d.intersects(r5)&&en4.isAlive==true))
		{
			if(v>=en3.y-100)
			  p.hp=p.hp-1;
			if (p.hp==0)
			  lost=true;
			if(p.hp<0)
				p.hp=0;
		}
		if((d.intersects(r6)&& en5.isAlive==true)||(d.intersects(r7)&&en6.isAlive==true))
		{
			if(v>=en5.y-100)
			  p.hp=p.hp-1;
			if (p.hp==0)
			  lost=true;
			if(p.hp<0)
				p.hp=0;
		}
		if(d.intersects(r3) && p.y==330)
		{
			
				ok=1;
				p.y=329;
				
				
			
		}
		else if(p.y==329 && p.x>=539 &&p.x<=785)
				 ok=2;			  
		else if(p.y==329 && (p.x<539 ||p.x>785))
			ok=3;
		else ok=0;
		
			 
			
		     
		
		
	}
 
	static Font font = new Font("SanSerif",Font.BOLD,24);	
	static Font font2 = new Font("SanSerif",Font.BOLD,60);
	public void paint(Graphics g){
		
		if (p.dy==3 && k==false)
		{
			k=true;
			animator=new Thread(this);
			animator.start();
		}
		super.paint(g);
			Graphics2D g2d = (Graphics2D) g;
		g2d.drawImage(img, 0, 0, null);
		g2d.drawImage(p.getImage(), p.getX(), v, null);
		if(en.Alive()==true)
				g2d.drawImage(en.getImage(),en.getX(),en.getY(),null);
		if(en2.Alive()==true)
			g2d.drawImage(en2.getImage(),en2.getX(),en2.getY(),null);
		if(en3.Alive()==true)
			g2d.drawImage(en3.getImage(),en3.getX(),en3.getY(),null);
		if(en4.Alive()==true)
			g2d.drawImage(en4.getImage(),en4.getX(),en4.getY(),null);
		if(en5.Alive()==true)
			g2d.drawImage(en5.getImage(),en5.getX(),en5.getY(),null);
		if(en6.Alive()==true)
			g2d.drawImage(en6.getImage(),en6.getX(),en6.getY(),null);
		if(healthpack.Alive()==true)
			g2d.drawImage(healthpack.getImage(),healthpack.getX(),healthpack.getY(),null);
		g2d.drawImage(p1.getImage(),p1.getX(),p1.getY(),null);
		g2d.setFont(font);
		g2d.setColor(Color.RED);
		g2d.drawString("Health :"+p.hp, 10, 740);
		g2d.setColor(Color.YELLOW);
		g2d.drawString("Score :"+p.score, 800, 740);
		
		if(lost){
			g2d.setFont(font2);
			g2d.setColor(Color.RED);
			g2d.drawString("YOU LOST", 500, 350);
			g2d.setFont(font);
			g2d.setColor(Color.RED);
			g2d.drawString("Press ESC to exit",550,450);
			
		}
		else {
			p.score++;
		}
	
		
	}
	private class AL extends KeyAdapter{
		 public void keyReleased(KeyEvent e){
			 p.keyReleased(e);
		 }
		 public void keyPressed(KeyEvent e){
			 p.keyPressed(e);
		 }
	}
	boolean h=false;
	boolean done=false;
	
	int hi=600;
	public void cycle() {
        if (h == false)
        	{
                v=v-3;
                p.y=v;
        }
        if (v == hi-300||ok==1||ok==3)
        {
              
                h = true;
                
                if(ok==1)
                	hi=v;
               
        }
        
      
        if (h == true && v <= 600) {
        	if(ok==0 || ok==3){
                v=v+3;
                if (v>600)
                	v=600;
                p.y=v;
        	}
        	     
        		 if(v==600 && ok==0)
        		 { done=true;
        		    hi=v;
        		 }
        		 else 
                   if (v == hi && ok==2) {
                        done = true;
                }
        }
        
	 }


	
	public void run() {
		long beforeTime, timeDiff, sleep;
		 
        beforeTime = System.currentTimeMillis();

        while (done == false) {

                cycle();

                timeDiff = System.currentTimeMillis() - beforeTime;
                sleep = 10 - timeDiff;

                if (sleep < 0)
                        sleep = 2;
                try {
                        Thread.sleep(sleep);
                } catch (Exception e) {
                        System.out.println("interrupted");
                }

                beforeTime = System.currentTimeMillis();
        }
        done = false;
        h = false;
        k= false;
        
		
	}

}

[Norm]

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at Game.Board.checkCollisions(Board.java:92)

What variable on line 92 is null?

[Tolls]

At some point in your code 'en' is set to null after the Board instance is created.