How Do I Implement Java Swing and JLabel?

[Scott Evans]

I have been writing a program that allows the user to select and then post items to a screen. It will also redraw the screen. It sets up fine the first time the classes are called. However, after redrawing the container, I cannot make a call to draw to the container from the object used to set it up. I have tried using JFrames, JPanels; a separate class. Is there a way to do this?

The object called to create the GUI is below.

public city()
{ 
 theWindow=new GUI();
 theWindow.setVisible(true);
 randomSet();
 draw();
}
 

The important GUI code is below.

My GUI creation is below. The code is long so not everything is shown.

package city;
 
import java.awt.BorderLayout;
import java.awt.Container;
import java.awt.event.*;
import java.util.ArrayList;
 
import javax.swing.JCheckBoxMenuItem;
import javax.swing.JFrame;
import javax.swing.JMenu;
import javax.swing.JMenuBar;
import javax.swing.JMenuItem;
 
public class GUI extends JFrame implements MouseListener, ActionListener, KeyListener{
 
     Container c;
    int gX[];
    int gY[];
    int lowX, lowXcoord, lowY, lowYcoord;
     JMenuBar menubar;
     JCheckBoxMenuItem pr;
     city game;
     private String object="null";
     JMenu file,residential,business,commercial,manufacturing,administration,re,removeobject;
     JMenuItem bull, save, offices, n,s,e,w, lowresidential, highresidential, lowcommerce, busb, highcommerce, factory,fire,police,padmin,hospital,school,power,garbage,water,waste,reset;
 
   public GUI(boolean inb)
   {
       boolean prev=inb;
   }
    public GUI()
    {
       paintGrid();
    }
 
     public void paintGrid()
     {
         setResizable(false);
            setTitle("City");
            c = getContentPane();
            setSize(700, 700);
            c.setLayout(new BorderLayout());
            menubar = new JMenuBar();
            c.add("North",menubar);
            c.addMouseListener(this);
 
            file = new JMenu("FILE");
            save=new JMenuItem("Save");
            save.addActionListener(this);
            file.add(save);
            n=new JMenuItem("Go North");
            n.addActionListener(this);
            file.add(n);
            s=new JMenuItem("Go South");
            s.addActionListener(this);
            file.add(s);
            e=new JMenuItem("Go East");
            e.addActionListener(this);
            file.add(e);
            w=new JMenuItem("Go West");
            w.addActionListener(this);
            file.add(w);
 
            residential= new JMenu("Residential");
            lowresidential=new JMenuItem("Small Res");
            lowresidential.addActionListener(this);
            residential.add(lowresidential);
            highresidential=new JMenuItem("Large Res");
            highresidential.addActionListener(this);
            residential.add(highresidential);
 
            business = new JMenu("Small Business");
            busb=new JMenuItem("Business");
            busb.addActionListener(this);
            business.add(busb);
 
            commercial = new JMenu("Commmercial Offices");
            lowcommerce=new JMenuItem("Small Office");
            lowcommerce.addActionListener(this);
            commercial.add(lowcommerce);
            highcommerce= new JMenuItem("Large Office");
            highcommerce.addActionListener(this);
            commercial.add(highcommerce);
 
            manufacturing = new JMenu("Manufacturing");
            factory=new JMenuItem("Factory");
            factory.addActionListener(this);
            manufacturing.add(factory);
 
            administration = new JMenu("Public Services");
            power=new JMenuItem("Power");
            power.addActionListener(this);
            administration.add(power);
            school=new JMenuItem("School");
            school.addActionListener(this);
            administration.add(school);
            fire= new JMenuItem("Fire");
            fire.addActionListener(this);
            administration.add(fire);
            police= new JMenuItem("Police");
            police.addActionListener(this);
            administration.add(police);
            water=new JMenuItem("Water");
            water.addActionListener(this);
            administration.add(water);
            garbage=new JMenuItem("Garbage");
            garbage.addActionListener(this);
            administration.add(garbage);
            waste=new JMenuItem("Waste Treatment");
            waste.addActionListener(this);
            administration.add(waste);
            padmin=new JMenuItem("Government Services");
            padmin.addActionListener(this);
            administration.add(padmin);
            hospital= new JMenuItem("Hospital");
            hospital.addActionListener(this);
            administration.add(hospital);
 
            removeobject= new JMenu("Remove Building");
            bull=new JMenuItem("Remove Object");
            bull.addActionListener(this);
            removeobject.add(bull);
 
            re= new JMenu("Reset All");
            re.addActionListener(this);
            reset=new JMenuItem("Reset Game");
            reset.addActionListener(this);
            re.add(reset);
 
            menubar.add(file);
            menubar.add(residential);
            menubar.add(business);
            menubar.add(commercial);
            menubar.add(manufacturing);
            menubar.add(administration);
            menubar.add(bull);
            menubar.add(re);
 
            setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
            paint grid = new paint(0,0,"grid");
            c.add(grid);
            c.validate();
     }
 
     public void actionPerformed(ActionEvent ae)
     {
             String theText= ((JMenuItem) ae.getSource()).getText();
 
             if(theText.equals("Remove Object"))
             {
                 object="remove";
             }
             else if(theText.equals("Reset Game"))
             {
                 object="reset";
                 c.repaint();
                 c.removeAll();
                 c.validate();
                 paintGrid();
                 randomizer res=new randomizer();
             }
 

Objects are added using the method below in the GUI class.

public void addObject(int inx, int iny, String inobj)
        {
           calcSnapX(inx);
           calcSnapY(iny);
           paint sq= new paint(getSnapX(), getSnapY(), inobj);
           c.add(sq);
           c.validate();
        }
 

This code is called using the following.

public city()
{ 
 theWindow=new GUI();
 theWindow.setVisible(true);
 randomSet();
 draw();
}
 

I used a paint class to draw the components. It is below.

package city;
 
import java.awt.*;
 
import javax.swing.JLabel;
import javax.swing.JPanel;
 
class paint extends JLabel{
 
    int x,y;
    int h,w;
    String object="null";
 
    public paint(int inx, int iny, String inobject)
    {
        if(inobject.equals("null"))
        {
        System.out.println("Select A Building and Building Type");
        }
        else 
        {
            x=inx;
            y=iny;
            object=inobject;
        }
        if(inobject.equals("plant"))
        {
            setForeground(Color.GREEN);
        }
        else if(inobject.equals("lake"))
        {
            setForeground(Color.BLUE);
        }
        else if(inobject.equals("mountain"))
        {
            setForeground(Color.BLACK);
        }
        else if(inobject.equals("bus"))
        {
        setForeground(Color.MAGENTA);
        }
        else if(inobject.equals("lowres"))
        {
         setForeground(Color.CYAN);    
        }
        else if(inobject.equals("highres"))
        {
         setForeground(Color.DARK_GRAY);    
        }
        else if(inobject.equals("soffice"))
        {
         setForeground(Color.CYAN);
        }
        else if(inobject.equals("loffice"))
        {
            setForeground(Color.DARK_GRAY);
        }
        else if(inobject.equals("grid")) {
            setForeground(Color.BLACK);
        }
    }
 
     protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            if(object.equals("null"))
            {
            System.out.println("Select A Building and Building Type");
            }
            else
            {
            if(object.equals("grid")) 
            {
               for(int i = 0;i<35;i++){
                g.drawLine(i*20, 0, i*20, 700);
                 g.drawLine(0, i*20, 700, i*20);
                }
             }
            else if(object.equals("plant"))
            {
                g.fillOval(x, y, 5, 5);
            }
            else if(object.equals("lake"))
            {
                g.fillOval(x, y, 50, 50);
            }
            else if(object.equals("bus"))
            {
               g.fillOval(x-6, y-27, 15, 15);
            }
            else if(object.equals("lowres"))
            {
                g.fillRect(x-6, y-27, 15, 15);
            }
            else if(object.equals("highres"))
            {
                g.fillRect(x-6, y-27, 15, 15);
            }
            else if(object.equals("soffice"))
            {
                 g.fillOval(x-6, y-27, 15, 15);
            }
            else if(object.equals("loffice"))
            {
                 g.fillOval(x-6, y-27, 15, 15);
            }
            }
     }
}
 
 

However, after redrawing the screen, I get the following error.

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
    at city.city.draw(city.java:183)
    at city.city.<init>(city.java:37)
    at city.randomizer.<init>(randomizer.java:7)
    at city.GUI.actionPerformed(GUI.java:160)
    at javax.swing.AbstractButton.fireActionPerformed(Unknown Source)
    at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source)
    at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source)
    at javax.swing.DefaultButtonModel.setPressed(Unknown Source)
    at javax.swing.AbstractButton.doClick(Unknown Source)
    at javax.swing.plaf.basic.BasicMenuItemUI.doClick(Unknown Source)
    at javax.swing.plaf.basic.BasicMenuItemUI$Handler.mouseReleased(Unknown Source)
    at java.awt.Component.processMouseEvent(Unknown Source)
    at javax.swing.JComponent.processMouseEvent(Unknown Source)
    at java.awt.Component.processEvent(Unknown Source)
    at java.awt.Container.processEvent(Unknown Source)
    at java.awt.Component.dispatchEventImpl(Unknown Source)
    at java.awt.Container.dispatchEventImpl(Unknown Source)
    at java.awt.Component.dispatchEvent(Unknown Source)
    at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source)
    at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source)
    at java.awt.LightweightDispatcher.dispatchEvent(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.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)