CODEWITHSUNDEEP
javanullpointerexceptioncolor-scheme
nullwriter
nullwriter

Reputation: 804

Get NullPointerException when trying to pass a Color argument from different classes

Basically I'm making a drawing board which you draw with your mouse; theres a set of color buttons to pick which are made in a custom class ColoredButton with a Color argument set by a setColor(int r,g,b).

So, in the class ColourToolbar when you click one of these ColoredButtons, it sets a global variable selectedCOlor to the color set in that button (explained above), and then the DrawBoard class uses getColor() to get the color in the 'selectedCOlor' variable inside ColourToolbar class.

Here are the classes (i took out code which is not needed for this):

public class ColoredButton extends JButton {

   public Color color;


   public ColoredButton(ImageIcon img){

       super(img);
   }

   public void setColor(int r, int g, int b){

       this.color = new Color(r,g,b);
   }

   public Color getColor(){

       return this.color;
   }

}

Next class:

public class ColourToolbar extends JPanel implements ActionListener{

public Color selectedColor;
public boolean colorSelected = false;

public ColoredButton pink,black,blue,green,orange,yellow,darkp,red,white;

public ColourToolbar(){

    setBackground(Color.DARK_GRAY);

    setLayout(new GridBagLayout());

    Dimension size = getPreferredSize();
    size.setSize(1024,80); //w, h
    setPreferredSize(size);

    // NOTE: There are 8 more blocks of codes like the one below, left for example.

    ImageIcon blackicon = new ImageIcon(getClass().getResource("Icons/Colours/Black.png"));
        black = new ColoredButton(new ImageIcon(blackicon.getImage().getScaledInstance(width, height, java.awt.Image.SCALE_SMOOTH)));
        gbc.gridx = 7;
        gbc.gridy = 0;
        gbc.fill = GridBagConstraints.HORIZONTAL;
        gbc.weightx = 0.5;    
        black.setColor(255, 255, 255);
        black.setOpaque(false);
        black.setContentAreaFilled(false);
        black.setBorderPainted(false);
        black.setActionCommand("orange");
        black.addActionListener(this);
        gbc.insets = new Insets(0,0,0,0); //top, left, bottom, right
        add(black, gbc);


}

@Override
public void actionPerformed(ActionEvent e){

    // all colors: black, blue, green, orange, *pink, yellow, darkpink, *red, white

    if("black".equalsIgnoreCase(e.getActionCommand())){

        this.selectedColor = black.getColor();
        System.out.println("black= " + selectedColor.toString());
        this.colorSelected = true;
    }      
}

public Color getCurrColor(){

    return this.selectedColor;
}


}

Last class where I get the NullPointerException:

public class DrawBoard extends JPanel implements MouseListener, MouseMotionListener{

public JLabel status;
private JLabel imgLabel; // this is where the drawing happens
private List<Point> points = new ArrayList<Point>();
private List<BufferedImage> lines = new ArrayList<BufferedImage>();

private static final int BI_WIDTH = 1024;
private static final int BI_HEIGHT = 800;

private BufferedImage bImage = new BufferedImage(BI_WIDTH, BI_HEIGHT,
        BufferedImage.TYPE_INT_ARGB);

public Color currentColor;

public DrawBoard(){  

   Graphics2D g2d = bImage.createGraphics();
   g2d.dispose();

    Dimension size = getPreferredSize();
    size.setSize(1024,800); //w, h
    setPreferredSize(size);
    status =  new JLabel("default");
    add(status, BorderLayout.SOUTH);
    addMouseListener(this);
    addMouseMotionListener(this);  


     imgLabel = new JLabel(new ImageIcon(bImage)) {
     @Override
     protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        paintInLabel(g);
     }
   };
     imgLabel.setOpaque(false);
     setOpaque(false);
      add(imgLabel, BorderLayout.CENTER);

}

private void paintInLabel(Graphics g) {
  Graphics2D g2d = (Graphics2D) g;
  g2d.setColor(getColor()); // this colour is when mouse is pressed
  g2d.setStroke(new BasicStroke(5));
  if (points.size() < 2) {
     return;
  }
  for (int i = 1; i < points.size(); i++) {
     int x1 = points.get(i - 1).x;
     int y1 = points.get(i - 1).y;
     int x2 = points.get(i).x;
     int y2 = points.get(i).y;
     g2d.drawLine(x1, y1, x2, y2);
  }
}

// Where the drawing happens
@Override
public void mousePressed(MouseEvent e) {
    status.setText("you pressed down the mouse");
    this.pstart = e.getPoint();
    points.add(e.getPoint());

}

@Override
public void mouseDragged(MouseEvent e) {
  status.setText("you draged the mouse");
  points.add(e.getPoint());
  imgLabel.repaint();
}

@Override
public void mouseReleased(MouseEvent e) {
    status.setText("you release the mouse click");
    Graphics2D g2d = bImage.createGraphics();
    g2d.setColor(getColor()); // this is the final colour - 
    g2d.setStroke(new BasicStroke(5));

     if (points.size() >= 2) {
        for (int i = 1; i < points.size(); i++) {
           int x1 = points.get(i - 1).x;
           int y1 = points.get(i - 1).y;
           int x2 = points.get(i).x;
           int y2 = points.get(i).y;
           g2d.drawLine(x1, y1, x2, y2);
        }
     }
     g2d.dispose();

     points.clear();
     imgLabel.repaint();

}
// End of where the drawing happens


// BELOW IN THIS METHOD IS WHERE it gets the NullPointerException
private Color getColor() {
    ColourToolbar ct = new ColourToolbar();
    System.out.println(ct.getCurrColor().toString());

    return  ct.getCurrColor();
}

private void setColor(Color col){

    this.currentColor = col;
}

}

Error stacktrace is here:

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
    at gui.DrawBoard.getColor(DrawBoard.java:162)
    at gui.DrawBoard.paintInLabel(DrawBoard.java:78)
    at gui.DrawBoard.access$000(DrawBoard.java:32)
    at gui.DrawBoard$1.paintComponent(DrawBoard.java:67)
    at javax.swing.JComponent.paint(JComponent.java:1054)
    at javax.swing.JComponent.paintChildren(JComponent.java:887)
    at javax.swing.JComponent.paint(JComponent.java:1063)
    at javax.swing.JComponent.paintChildren(JComponent.java:887)
    at javax.swing.JComponent.paint(JComponent.java:1063)
    at javax.swing.JComponent.paintChildren(JComponent.java:887)
    at javax.swing.JComponent.paint(JComponent.java:1063)
    at javax.swing.JComponent.paintChildren(JComponent.java:887)
    at javax.swing.JComponent.paint(JComponent.java:1063)
    at javax.swing.JLayeredPane.paint(JLayeredPane.java:585)
    at javax.swing.JComponent.paintChildren(JComponent.java:887)
    at javax.swing.JComponent.paintToOffscreen(JComponent.java:5228)
    at javax.swing.BufferStrategyPaintManager.paint(BufferStrategyPaintManager.java:295)
    at javax.swing.RepaintManager.paint(RepaintManager.java:1206)
    at javax.swing.JComponent.paint(JComponent.java:1040)
    at java.awt.GraphicsCallback$PaintCallback.run(GraphicsCallback.java:39)
    at sun.awt.SunGraphicsCallback.runOneComponent(SunGraphicsCallback.java:78)
    at sun.awt.SunGraphicsCallback.runComponents(SunGraphicsCallback.java:115)
    at java.awt.Container.paint(Container.java:1967)
    at java.awt.Window.paint(Window.java:3877)
    at javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:781)
    at javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:728)
    at javax.swing.RepaintManager.prePaintDirtyRegions(RepaintManager.java:677)
    at javax.swing.RepaintManager.access$700(RepaintManager.java:59)
    at javax.swing.RepaintManager$ProcessingRunnable.run(RepaintManager.java:1621)
    at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:251)
    at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:721)
    at java.awt.EventQueue.access$200(EventQueue.java:103)
    at java.awt.EventQueue$3.run(EventQueue.java:682)
    at java.awt.EventQueue$3.run(EventQueue.java:680)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
    at java.awt.EventQueue.dispatchEvent(EventQueue.java:691)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:244)
    at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:163)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:151)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:147)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:139)
    at java.awt.EventDispatchThread.run(EventDispatchThread.java:97)

Upvotes: 0

Views: 1592

Answers (1)

Jon Skeet
Jon Skeet

Reputation: 1500953

Okay, this is the problem:

ColourToolbar ct = new ColourToolbar();
System.out.println(ct.getCurrColor().toString());

getCurrColor() returns selectedColor within the ColourToolbar... but you haven't got a selectedColor... the constructor doesn't set it to anything. So the value is null, and when you call toString() you'll get the exception.

In your description you say:

it sets a global variable selectedCOlor

but selectedColor isn't a "global" variable - it's an instance variable; each ColourToolbar instance has a separate selectedColor variable.

Why are you doing this on a new ColourToolbar though? Don't you actually want to fetch the selected colour from an existing toolbar? Or if you really want it to be global (ick) it should be a static variable, fetched by a static method without you creating a new instance at all.

Upvotes: 5

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