java - 2D Shooter using JPanel/JFrame. drawImage (bullet) on screen with it's own velocity -

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here have:

import java.awt.color; import java.awt.component; import java.awt.graphics; import java.awt.image; import java.awt.toolkit; import java.awt.event.actionevent; import java.awt.event.actionlistener; import java.awt.event.keyevent; import java.awt.event.keylistener; import java.awt.image.imageobserver; import java.util.arraylist; import javax.swing.jpanel;  public class gamepanel extends jpanel implements actionlistener, keylistener, imageobserver {         public image ship;         public image enemy;         private int xloc;         private int yloc = 180;         private int xloc2 = 700;         private int yloc2 = 180;         private int xvel;         private int yvel;         private int xvel_en;         private int xvel_sh = 6;         private imageobserver observer = null;         private arraylist<base> shield = new arraylist<base>();         private image shieldpiece;         private shot shot;          public gamepanel()  {             ship = toolkit.getdefaulttoolkit().createimage("ship3.png");             enemy = toolkit.getdefaulttoolkit().createimage("alien-ship-1.png");             shieldpiece = toolkit.getdefaulttoolkit().createimage("block2.png");              for(int x = 500; x < 680; x = x + 18)                 for(int y = 60; y < 370; y = y + 18)    {                     base temp = new base(x,y);                     shield.add(temp);                 }         }          public void paint(graphics g){             super.paint(g);             g.drawimage(ship, xloc, yloc, null);             g.drawimage(enemy, xloc2, yloc2, null);              for(base b: shield)                 g.drawimage(shieldpiece, b.getshieldx(), b.getshieldy(), null);         }          @override         public void actionperformed(actionevent arg0) {             // todo auto-generated method stub              move();             setbackground(color.black);             repaint();          }          private void move() {              int endofwindow = getwidth();             int endofwindow1 = getheight();             if(xloc>=(endofwindow - ship.getwidth(null))|| xloc<0)                 xvel = -xvel;             xloc +=xvel;                 if(xloc>=(endofwindow - ship.getwidth(null)))                 xvel = -xvel;             xloc +=xvel;             if(yloc>=(endofwindow1 - ship.getheight(null)) || yloc<0)                 yvel = -yvel;             yloc +=yvel;             if(yloc>=(endofwindow1 - ship.getheight(null)))                 yvel = -yvel;             yloc +=yvel;          }          @override         public void keypressed(keyevent arg0) {             // todo auto-generated method stub              if(arg0.getkeycode() == keyevent.vk_d)                 xvel = 3;             if(arg0.getkeycode() == keyevent.vk_a)                 xvel = -3;             if(arg0.getkeycode() == keyevent.vk_w)                 yvel = -3;             if(arg0.getkeycode() == keyevent.vk_s)                 yvel = 3;              if(arg0.getkeycode() == keyevent.vk_right)                 xvel = 3;             if(arg0.getkeycode() == keyevent.vk_left)                 xvel = -3;             if(arg0.getkeycode() == keyevent.vk_up)                 yvel = -3;             if(arg0.getkeycode() == keyevent.vk_down)                 yvel = 3;              if(arg0.getkeycode() == keyevent.vk_space)  {                 shot shoot = new shot(xvel_sh, xloc, yloc);                 shoot.paint();              }           }          @override         public void keyreleased(keyevent arg0) {             // todo auto-generated method stub              if(arg0.getkeycode() == keyevent.vk_d || arg0.getkeycode() == keyevent.vk_a)                 xvel = 0;             if(arg0.getkeycode() == keyevent.vk_w || arg0.getkeycode() == keyevent.vk_s)                 yvel = 0;              if(arg0.getkeycode() == keyevent.vk_right || arg0.getkeycode() == keyevent.vk_left)                 xvel = 0;             if(arg0.getkeycode() == keyevent.vk_up || arg0.getkeycode() == keyevent.vk_down)                 yvel = 0;          }          @override         public void keytyped(keyevent arg0) {             // todo auto-generated method stub          } }

and shot class:

import java.awt.graphics; import java.awt.image; import java.awt.toolkit;   public class shot{     private int xvel_sh;     private int xcoord;     private int ycoord;     private image shot;     private graphics g;      public shot(int vel, int xloc, int yloc)    {         vel = xvel_sh;         xcoord = xloc;         ycoord = yloc;         shot = toolkit.getdefaulttoolkit().createimage("shot4.png");     }      public void setshotvel(int shotvel) {         xvel_sh = shotvel;     }      public void paint() {         g.drawimage(shot, xcoord, ycoord, null);     } }

i have set when hit space, should create shot object, call paint() method in shot class. shot object created @ xloc , yloc (from gamepanel class - location of "ship" or player).

however, lot of errors, starting nullpointerexception when hit space. game not crash, keeps coming null pointer exception.' followed error:

exception in thread "awt-eventqueue-0" java.lang.nullpointerexception     @ shot.paint(shot.java:25)     @ gamepanel.keypressed(gamepanel.java:104)     @ java.awt.component.processkeyevent(unknown source)     @ java.awt.component.processevent(unknown source)     @ java.awt.container.processevent(unknown source)     @ java.awt.window.processevent(unknown source)     @ java.awt.component.dispatcheventimpl(unknown source)     @ java.awt.container.dispatcheventimpl(unknown source)     @ java.awt.window.dispatcheventimpl(unknown source)     @ java.awt.component.dispatchevent(unknown source)     @ java.awt.keyboardfocusmanager.redispatchevent(unknown source)     @ java.awt.defaultkeyboardfocusmanager.dispatchkeyevent(unknown source)     @ java.awt.defaultkeyboardfocusmanager.predispatchkeyevent(unknown source)     @ java.awt.defaultkeyboardfocusmanager.typeaheadassertions(unknown source)     @ java.awt.defaultkeyboardfocusmanager.dispatchevent(unknown source)     @ java.awt.component.dispatcheventimpl(unknown source)     @ java.awt.container.dispatcheventimpl(unknown source)     @ java.awt.window.dispatcheventimpl(unknown source)     @ java.awt.component.dispatchevent(unknown source)     @ java.awt.eventqueue.dispatcheventimpl(unknown source)     @ java.awt.eventqueue.access$200(unknown source)     @ java.awt.eventqueue$3.run(unknown source)     @ java.awt.eventqueue$3.run(unknown source)     @ java.security.accesscontroller.doprivileged(native method)     @ java.security.protectiondomain$1.dointersectionprivilege(unknown source)     @ java.security.protectiondomain$1.dointersectionprivilege(unknown source)     @ java.awt.eventqueue$4.run(unknown source)     @ java.awt.eventqueue$4.run(unknown source)     @ java.security.accesscontroller.doprivileged(native method)     @ java.security.protectiondomain$1.dointersectionprivilege(unknown source)     @ java.awt.eventqueue.dispatchevent(unknown source)     @ java.awt.eventdispatchthread.pumponeeventforfilters(unknown source)     @ java.awt.eventdispatchthread.pumpeventsforfilter(unknown source)     @ java.awt.eventdispatchthread.pumpeventsforhierarchy(unknown source)     @ java.awt.eventdispatchthread.pumpevents(unknown source)     @ java.awt.eventdispatchthread.pumpevents(unknown source)     @ java.awt.eventdispatchthread.run(unknown source)

not sure why not being drawn...can help? also, need implement object collisions (with shield class not shown here)...so if has direction towards tutorials on that? :p

g never initialized in shot, when call g.drawimage throws nullpointerexception.


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