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Thread: Null pointer exception

  1. #1
    Junior Member Wrathgarr's Avatar
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    Default Null pointer exception

    Hey folks,
    So I've been working a little program that draws maps. It reads in a CSV file with city names, coordinates, distances, and interconnecting highways. Its supposed to draw red lines (highways) between black dots (cities). However, I keep getting a null pointer exception, and I can't figure it out! here's my code so far, and I'll attach the CSV.

    here's the main program:

    package Maps2;
     
    import java.awt.Color;
    import java.awt.Graphics;
    import java.awt.event.MouseEvent;
    import java.io.File;
    import javax.swing.JFileChooser;
    import javax.swing.JPanel;
     
    /**
     *
     * @author stu696084
     */
    public class Map extends javax.swing.JFrame {
     
      JFileChooser fileChooser = new JFileChooser();
      public City start;
      public City end;
        /** Creates new form Map */
        public Map() {
            initComponents();}
            public class MyPanel extends JPanel {
      @Override
            @SuppressWarnings("static-access")
           public void paint(Graphics g) {
               super.paint(g);
               for(City c: City.cities) {
                     Color z= Color.BLACK;
     
                   if (c == start){
                       z = Color.RED;
     
     
                   }
                   else if (c == end) {
                         z = Color.BLUE;
                   }
                     g.setColor(z);
                     g.fillOval((int)start.p.px, (int)start.p.py, 15, 15);
                     g.setColor(Color.RED);
                     g.drawLine((int)start.p.px, (int)start.p.py, (int)end.p.px, (int)end.p.py);
               }
     
               // Place code to draw the map here
               }
           }
     
     
     
        /** This method is called from within the constructor to
         * initialize the form.
         * WARNING: Do NOT modify this code. The content of this method is
         * always regenerated by the Form Editor.
         */
        @SuppressWarnings("unchecked")
        // <editor-fold defaultstate="collapsed" desc="Generated Code">                          
        private void initComponents() {
     
            theMap = new MyPanel();
            loadMap = new javax.swing.JButton();
            showMap = new javax.swing.JButton();
            showDirections = new javax.swing.JButton();
            jLabel1 = new javax.swing.JLabel();
     
            setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
     
            theMap.setBackground(new java.awt.Color(102, 204, 0));
            theMap.setPreferredSize(new java.awt.Dimension(1000, 650));
            theMap.addMouseListener(new java.awt.event.MouseAdapter() {
                public void mouseClicked(java.awt.event.MouseEvent evt) {
                    theMapMouseClicked(evt);
                }
            });
     
            org.jdesktop.layout.GroupLayout theMapLayout = new org.jdesktop.layout.GroupLayout(theMap);
            theMap.setLayout(theMapLayout);
            theMapLayout.setHorizontalGroup(
                theMapLayout.createParallelGroup(org.jdesktop.layout.GroupLayout.LEADING)
                .add(0, 1000, Short.MAX_VALUE)
            );
            theMapLayout.setVerticalGroup(
                theMapLayout.createParallelGroup(org.jdesktop.layout.GroupLayout.LEADING)
                .add(0, 650, Short.MAX_VALUE)
            );
     
            loadMap.setText("Load Map");
            loadMap.addActionListener(new java.awt.event.ActionListener() {
                public void actionPerformed(java.awt.event.ActionEvent evt) {
                    loadMapActionPerformed(evt);
                }
            });
     
            showMap.setText("Show Map");
            showMap.addActionListener(new java.awt.event.ActionListener() {
                public void actionPerformed(java.awt.event.ActionEvent evt) {
                    showMapActionPerformed(evt);
                }
            });
     
            showDirections.setText("Show Directions");
            showDirections.addActionListener(new java.awt.event.ActionListener() {
                public void actionPerformed(java.awt.event.ActionEvent evt) {
                    showDirectionsActionPerformed(evt);
                }
            });
     
            jLabel1.setText("jLabel1");
     
            org.jdesktop.layout.GroupLayout layout = new org.jdesktop.layout.GroupLayout(getContentPane());
            getContentPane().setLayout(layout);
            layout.setHorizontalGroup(
                layout.createParallelGroup(org.jdesktop.layout.GroupLayout.LEADING)
                .add(layout.createSequentialGroup()
                    .add(layout.createParallelGroup(org.jdesktop.layout.GroupLayout.LEADING)
                        .add(layout.createSequentialGroup()
                            .add(50, 50, 50)
                            .add(theMap, org.jdesktop.layout.GroupLayout.PREFERRED_SIZE, org.jdesktop.layout.GroupLayout.DEFAULT_SIZE, org.jdesktop.layout.GroupLayout.PREFERRED_SIZE)
                            .add(52, 52, 52)
                            .add(layout.createParallelGroup(org.jdesktop.layout.GroupLayout.LEADING)
                                .add(showMap)
                                .add(loadMap)
                                .add(showDirections)))
                        .add(layout.createSequentialGroup()
                            .add(464, 464, 464)
                            .add(jLabel1, org.jdesktop.layout.GroupLayout.PREFERRED_SIZE, 310, org.jdesktop.layout.GroupLayout.PREFERRED_SIZE)))
                    .addContainerGap(80, Short.MAX_VALUE))
            );
            layout.setVerticalGroup(
                layout.createParallelGroup(org.jdesktop.layout.GroupLayout.LEADING)
                .add(layout.createSequentialGroup()
                    .add(6, 6, 6)
                    .add(jLabel1, org.jdesktop.layout.GroupLayout.PREFERRED_SIZE, 23, org.jdesktop.layout.GroupLayout.PREFERRED_SIZE)
                    .addPreferredGap(org.jdesktop.layout.LayoutStyle.UNRELATED)
                    .add(layout.createParallelGroup(org.jdesktop.layout.GroupLayout.LEADING)
                        .add(layout.createSequentialGroup()
                            .add(loadMap)
                            .add(34, 34, 34)
                            .add(showMap)
                            .add(29, 29, 29)
                            .add(showDirections))
                        .add(theMap, org.jdesktop.layout.GroupLayout.PREFERRED_SIZE, org.jdesktop.layout.GroupLayout.DEFAULT_SIZE, org.jdesktop.layout.GroupLayout.PREFERRED_SIZE))
                    .addContainerGap(41, Short.MAX_VALUE))
            );
     
            pack();
        }// </editor-fold>                        
     
        private void loadMapActionPerformed(java.awt.event.ActionEvent evt) {                                        
          int retval = fileChooser.showOpenDialog(this);
          if (retval == JFileChooser.APPROVE_OPTION) {
                File file = fileChooser.getSelectedFile();
            Input.readFile(file);
          }
            // TODO add your handling code here:
        }                                       
     
        private void showMapActionPerformed(java.awt.event.ActionEvent evt) {                                        
     
     
                for (City c : City.cities) {
                    System.out.println(c.name + " Is at " + c.p.px + ", " + c.p.py);
     
     
                    for (Road r : c.roads) {
                        System.out.println("  Road " + r.name + " Goes to " + r.endCity.name + " (" + r.length + ", " + r.time + ")");
     
                    }
     
     
            }  // TODO add your handling code here:
            // TODO add your handling code here:
        }                                       
     
        private void showDirectionsActionPerformed(java.awt.event.ActionEvent evt) {                                               
            // TODO add your handling code here:
        }                                              
     
        private void theMapMouseClicked(java.awt.event.MouseEvent evt) {                                    
           for(City c : City.cities) {
     
               if(Point.close(evt.getX(), evt.getY())==true) {
                   c = start;
               }
               else if (c==start) {
                   c = end;
               }
           }
            // TODO add your handling code here:
        }                                   
     
        /**
        * @param args the command line arguments
        */
        public static void main(String args[]) {
            java.awt.EventQueue.invokeLater(new Runnable() {
                public void run() {
                    new Map().setVisible(true);
                }
            });
        }
     
        // Variables declaration - do not modify                     
        private javax.swing.JLabel jLabel1;
        private javax.swing.JButton loadMap;
        private javax.swing.JButton showDirections;
        private javax.swing.JButton showMap;
        private javax.swing.JPanel theMap;
        // End of variables declaration                   
     
    }

    Here's the City and Road classes
    package Maps2;
     
    import java.util.ArrayList;
     
    /**
     *
     * @author stu696084
     */
    public class City {
     
        public Point p;
        public String name;
        public static ArrayList<City> cities = new ArrayList<City>();
        public ArrayList<Road> roads = new ArrayList<Road>();
     
        public City(String name, int x, int y) {
            this.name = name;
            this.p = new Point(x, y);
     
            cities.add(this);
     
        }
     
        public boolean isCity(String s) {
            return s.equals(name);
        }
     
        public static City findCity(String s) {
            for (City c : cities) {
                if (c.isCity(s)) {
                    return c;
                }
            }
            return null;
        }
     
        public static void Clear() {
            City.cities.clear();
        }
    }

    package Maps2;
     
    /**
     *
     * @author stu696084
     */
    public class Road {
     
        public City startCity, endCity;
        public int length, time;
        public String name;
     
        public Road(String name, City startCity, City endCity, int length, int time) {
            this.startCity = startCity;
            this.endCity = endCity;
            this.length = length;
            this.time = time;
            this.name = name;
        }
     
        @Override
        public String toString() {
            return (startCity + "and" + endCity);
        }
    }

    and finally the Input and Point classes:

    package Maps2;
     
    import java.io.BufferedReader;
    import java.io.File;
    import java.io.FileReader;
     
    /**
     *
     * @author stu696084
     */
    public class Input {
     
        public static void readFile(File file) {
            City.Clear();
     
            try {
                BufferedReader reader = new BufferedReader(new FileReader(file));
                String s;
                Boolean road = false;
                while ((s = reader.readLine()) != null) {
                    String[] strings = s.split(",");
                    if (strings.length == 0) {
                        System.out.println("nothin");
                        road = true;
                    } else if (road == false) {
                        City c = new City(strings[0], Integer.parseInt(strings[1]), Integer.parseInt(strings[2]));
     
     
     
                    } else {
                        Road r = new Road(strings[0], City.findCity(strings[1]), City.findCity(strings[2]), Integer.parseInt(strings[3]), Integer.parseInt(strings[4]));
                        Road r2 = new Road(strings[0], City.findCity(strings[2]), City.findCity(strings[1]), Integer.parseInt(strings[3]), Integer.parseInt(strings[4]));
                        r.startCity.roads.add(r);
                        r2.startCity.roads.add(r2);
                    }
     
                }
            } catch (Exception e) {
                System.out.println("File Error");
            }
        }
     
    }

    package Maps2;
     
    /**
     *
     * @author stu696084
     */
    public class Point {
     
        static double px, py;
    double x, y;
        @SuppressWarnings("static-access")
        public Point(double x, double y) {
            this.x = x;
            this.y = y;
            this.px = x * 2;
            this.py = y * 1.3 - 30;
        }
     
        public static boolean close(double mousex, double mousey) {
            return (mousex - px) * mousex - px + (mousey - py) * (mousey - py) < 25;
     
        }
     
        @Override
        public String toString() {
            return "(" + x + "," + y + ")";
        }
    }


    And I think the CSV is attached, but let me know if it doesn't work for you.
    Any help on this would be great guys, thanks a lot!


  2. #2
    Junior Member
    Join Date
    Mar 2010
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    Default Re: Null pointer exception

    Where are you exactly getting the Null pointer exception, it's too difficult to trace the whole program for me as i have not much time. Thanks for if you will be able to tell that in what area, this exception is being occured???

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