AWT-EventQueue-0 java.lang.NullPointerException when connecting to another class -

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basically i've got error:

run:exception in thread "awt-eventqueue-0" java.lang.nullpointerexception     @ paintv2.uipanel$1.actionperformed(paintgui.java:line marked)     @ javax.swing.abstractbutton.fireactionperformed(abstractbutton.java:2022)     @ javax.swing.abstractbutton$handler.actionperformed(abstractbutton.java:2346)     @ javax.swing.defaultbuttonmodel.fireactionperformed(defaultbuttonmodel.java:402)     @ javax.swing.defaultbuttonmodel.setpressed(defaultbuttonmodel.java:259)     @ javax.swing.plaf.basic.basicbuttonlistener.mousereleased(basicbuttonlistener.java:252)     @ java.awt.component.processmouseevent(component.java:6527)     @ javax.swing.jcomponent.processmouseevent(jcomponent.java:3321)     @ java.awt.component.processevent(component.java:6292)     @ java.awt.container.processevent(container.java:2234)     @ java.awt.component.dispatcheventimpl(component.java:4883)     @ java.awt.container.dispatcheventimpl(container.java:2292)     @ java.awt.component.dispatchevent(component.java:4705)     @ java.awt.lightweightdispatcher.retargetmouseevent(container.java:4898)     @ java.awt.lightweightdispatcher.processmouseevent(container.java:4533)     @ java.awt.lightweightdispatcher.dispatchevent(container.java:4462)     @ java.awt.container.dispatcheventimpl(container.java:2278)     @ java.awt.window.dispatcheventimpl(window.java:2739)     @ java.awt.component.dispatchevent(component.java:4705)     @ java.awt.eventqueue.dispatcheventimpl(eventqueue.java:746)     @ java.awt.eventqueue.access$400(eventqueue.java:97)     @ java.awt.eventqueue$3.run(eventqueue.java:697)     @ java.awt.eventqueue$3.run(eventqueue.java:691)     @ java.security.accesscontroller.doprivileged(native method)     @ java.security.protectiondomain$1.dointersectionprivilege(protectiondomain.java:75)     @ java.security.protectiondomain$1.dointersectionprivilege(protectiondomain.java:86)     @ java.awt.eventqueue$4.run(eventqueue.java:719)     @ java.awt.eventqueue$4.run(eventqueue.java:717)     @ java.security.accesscontroller.doprivileged(native method)     @ java.security.protectiondomain$1.dointersectionprivilege(protectiondomain.java:75)     @ java.awt.eventqueue.dispatchevent(eventqueue.java:716)     @ java.awt.eventdispatchthread.pumponeeventforfilters(eventdispatchthread.java:201)     @ java.awt.eventdispatchthread.pumpeventsforfilter(eventdispatchthread.java:116)     @ java.awt.eventdispatchthread.pumpeventsforhierarchy(eventdispatchthread.java:105)     @ java.awt.eventdispatchthread.pumpevents(eventdispatchthread.java:101)     @ java.awt.eventdispatchthread.pumpevents(eventdispatchthread.java:93)     @ java.awt.eventdispatchthread.run(eventdispatchthread.java:82)'

i trying link gui colour class making paint application. questions are: has gone wrong code? , if knows how fix it, can explain how fixed please

my main method:

package paintv2;  import javax.swing.*; import java.awt.*; import java.awt.event.*; import java.util.hashmap;   public class paintgui{      public static void main(string[] args ){          jframe frame = new jframe("test panel 2");          mainpanel panel = new mainpanel();          uipanel uip = new uipanel(panel);          frame.setlayout(new borderlayout());         frame.add(uip, borderlayout.north);          frame.add(panel, borderlayout.center);         frame.setsize(900, 900);          frame.setdefaultcloseoperation(jframe.exit_on_close);         frame.setvisible(true);     }  }

my mainpanel class:

class mainpanel extends jpanel {        int px, py; // radius     public color colvals;     public colour col;      public mainpanel(){                 this.addmousemotionlistener(new mousemotionadapter() {             // store drag coordinates , repaint                 public void mousedragged( mouseevent event )                 {                         px = event.getx();                         py = event.gety();                         repaint();                 }                 }); // end call addmousemotionlistener     }      public void paint( graphics g )     {                g.setcolor(color.red);          g.filloval( px, py, 15, 15 );     } }

my uipanel class: 

class uipanel extends jpanel {     public mainpanel gpanel;     public integer data;     public color colval;     public colour col;      public uipanel(mainpanel panel) {         gpanel = panel;          box btnbox = box.createhorizontalbox();         btnbox.add(box.createhorizontalglue());         jbutton setbtn = new jbutton("set");          //code colour chooser         //decided use dropdow list hashmap         final defaultcomboboxmodel colour = new defaultcomboboxmodel();         colour.addelement("red");         colour.addelement("blue");         colour.addelement("yellow");         colour.addelement("green");         final jcombobox colours = new jcombobox(colour);         jscrollpane colourscroll = new jscrollpane(colours);           jbutton freebtn = new jbutton("freehand");         jbutton rectbtn = new jbutton("rectangle");         jbutton circbtn = new jbutton("circle");         jbutton linebtn = new jbutton("line");          btnbox.add(setbtn);         btnbox.add(colourscroll);         btnbox.add(freebtn);         btnbox.add(rectbtn);         btnbox.add(circbtn);         btnbox.add(linebtn);         btnbox.setsize(300, 100);         btnbox.add(box.createhorizontalglue());          add(btnbox, borderlayout.north);          setbtn.addactionlistener(new actionlistener(){              public void actionperformed(actionevent e) {                  data= colours.getselectedindex();                  col.setcol(data);//this error being flagged                           }         });     } }

and colour class

package paintv2;  import java.awt.*; import java.awt.event.*; import java.util.hashmap; import javax.swing.*;  public class colour{      public color colval;       hashmap<integer, color> map = new hashmap<integer, color>();      public colour() {          map.put(0, color.red);         map.put(1, color.blue);         map.put(2, color.yellow);         map.put(3, color.green);      }      public color setcol(integer data) {         return map.get(data);     } }

sorry in advance massive chunks of code , code being messy. if need me edit bits out make more understandable, post or , edit when able to.

seems declared col , not initialized. try this..

public void actionperformed(actionevent e) {      data= colours.getselectedindex();     if(col == null)         col = new colour();     col.setcol(data);//this error being flagged                }

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