获取空指针异常

时间：2013-11-02 20:15:25

标签： java swing null

在MouseDragged函数中获取空指针异常。一直试图弄清楚是什么导致它，但我不知道是什么。任何帮助将不胜感激。我的程序应该添加一个图像文件，并能够绘制它。

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.io.*;
import javax.imageio.*;
import java.awt.image.BufferedImage;
import javax.swing.colorchooser.ColorSelectionModel;
import javax.swing.event.ChangeEvent;
import javax.swing.event.ChangeListener;
import java.awt.event.AdjustmentEvent;
import java.awt.event.AdjustmentListener;
import java.awt.geom.*;
import java.util.Vector;
import java.util.*;
import java.awt.Point;
import java.awt.Stroke;
import java.awt.Toolkit;
public class Lab3 {


public static void main(String[] args)
   {

  new Lab3Frame();

}


}
 class Lab3Frame extends JFrame implements ActionListener, MouseListener,     MouseMotionListener, ChangeListener
{

JFrame frame;
JPanel toolbar;
JMenuBar menuBar;
JMenu tool, file;
JLabel image;
JToggleButton b1, b2, b3, b4, bcol;

JMenuItem pencil, eraser, brush, line, open;
final JFileChooser fc = new JFileChooser();
BufferedImage img;
JColorChooser tcc;
  JScrollBar hbar, vbar;


  PaintPanel inkPanel;
  private Point[] stroke;
 public Color ink_color = Color.black;
 public Stroke ink_stroke = new BasicStroke(5.0f,
        BasicStroke.CAP_ROUND, BasicStroke.JOIN_ROUND);
  final int MAX_SAMPLES = 500;
  private int sampleCount;
//private Vector<Line2D.Double> v;

Lab3Frame(){
  frame = new JFrame();
  menuBar = new JMenuBar();
  image = new JLabel();
   tool = new JMenu("Tools");
   file = new JMenu("File");
   pencil = new JMenuItem("Pencil");
   eraser = new JMenuItem("Eraser");
   brush = new JMenuItem("Brush");
   line = new JMenuItem("Line");
   tool.add(pencil);
   tool.add(line);
   tool.add(eraser);
   tool.add(brush);
   open = new JMenuItem("Open");
   file.add(open);
   menuBar.add(file);
   menuBar.add(tool);
   frame.setJMenuBar(menuBar);
   tcc = new JColorChooser();

  inkPanel = new PaintPanel();
  toolbar = new JPanel();
  toolbar.setSize(100,300);

  image.setBackground(Color.blue);
  //TOOLBAR BUTTONS
  toolbar.setLayout(new BoxLayout(toolbar, BoxLayout.Y_AXIS));
      b1 = new JToggleButton("1");
  toolbar.add(b1);
  b2 = new JToggleButton("2");
  toolbar.add(b2);
  b3 = new JToggleButton("3");
  toolbar.add(b3);
  b4 = new JToggleButton("4");
  toolbar.add(b4);
  bcol = new JToggleButton(" ");
  toolbar.add(bcol);
  tcc.setPreviewPanel(new JPanel());

  //LISTENERS
  pencil.addActionListener(this);
  open.addActionListener(this);
  image.addMouseMotionListener(this);
  pencil.addMouseMotionListener(this);
  tcc.getSelectionModel().addChangeListener(this);
  inkPanel.addMouseMotionListener(this);
  inkPanel.addMouseListener(this);
  //hbar.addAdjustmentListener(this);
  //vbar.addAdjustmentListener(this);
  //tcc.addChangeListener(this);
  //ADD ELEMENTS TO FRAME
  frame.setSize(600, 600);
  hbar = new JScrollBar(JScrollBar.HORIZONTAL, 30, 20, 0, 300);
  vbar = new JScrollBar(JScrollBar.VERTICAL, 30, 40, 0, 300);

  frame.setLayout(new BorderLayout());
  image.setLayout(new BorderLayout());

  image.setBackground(Color.white);
  frame.add(toolbar, BorderLayout.WEST);
  frame.add(tcc, BorderLayout.SOUTH);
  frame.add(image, BorderLayout.CENTER); 
  frame.setGlassPane(inkPanel);
  frame.setVisible(true);
}




public void actionPerformed(ActionEvent e) {
if (e.getSource() == open){
int returnVal = fc.showOpenDialog(Lab3Frame.this);

 if (returnVal == JFileChooser.APPROVE_OPTION) {
           File file = fc.getSelectedFile();
          try {
                   // frame.add(inkPanel);
                    img=ImageIO.read(file);
                    ImageIcon icon=new ImageIcon(img); // ADDED
                    image.setIcon(icon); // ADDED

                    Dimension imageSize = new Dimension(icon.getIconWidth(),icon.getIconHeight()); // ADDED
                    image.setPreferredSize(imageSize); // ADDED
                    image.setVisible(true);
                    //
                    //image.add(hbar, BorderLayout.SOUTH);
                    //image.add(vbar, BorderLayout.EAST);
                    //image.revalidate(); // ADDED
                    //image.repaint(); // ADDED

                }
                catch(IOException e1) {
                e1.printStackTrace();
                }
            }
}

}

  public void stateChanged(ChangeEvent changeEvent) {
    Color customCol = tcc.getColor();
    bcol.setBackground(customCol);
  }

/*  
AdjustmentListener adjustmentListener = new AdjustmentListener(){

public void adjustmentValueChanged(AdjustmentEvent adjustmentEvent) {
    System.out.println("Adjusted: " + adjustmentEvent.getValue());
  }
};
*/
  public void mouseClicked(MouseEvent me) {
     int x = me.getX();
 int y = me.getY();

    if (SwingUtilities.isLeftMouseButton(me))
      {
         stroke[sampleCount] = new Point(x, y);
         int x1 = (int)stroke[sampleCount - 1].getX();
         int y1 = (int)stroke[sampleCount - 1].getY();
         int x2 = (int)stroke[sampleCount].getX();
         int y2 = (int)stroke[sampleCount].getY();
         if (sampleCount < MAX_SAMPLES - 1)
            ++sampleCount;

         // draw ink trail from previous point to current point
         inkPanel.drawInk(x1, y1, x2, y2);
      }
  }
   public void mouseEntered(MouseEvent me) {}
   public void mouseExited(MouseEvent me) {}
       public void mousePressed(MouseEvent me) {
   int x = me.getX();
    int y = me.getY();

    stroke[sampleCount] = new Point(x, y);
      if (sampleCount < MAX_SAMPLES - 1)
         ++sampleCount;
}

  public void mouseDragged(MouseEvent me) {

sampleCount = 1;
int x = me.getX();
    int y = me.getY();
System.out.println("y2:" + y );
 if (SwingUtilities.isLeftMouseButton(me))
  {
 // try{
     stroke[sampleCount] = new Point(x, y);
     int x2 = (int)stroke[sampleCount].getX();
     int y2 = (int)stroke[sampleCount].getY();
     int x1 = (int)stroke[sampleCount - 1].getX();
     int y1 = (int)stroke[sampleCount - 1].getY();

     if (sampleCount < MAX_SAMPLES - 1){
        ++sampleCount;}
        //draw.Line2D.
         inkPanel.drawInk(x1, y1, x2, y2);
         //inkPanel.repaint();

        }
    /*catch ( Exception err1 ) {
       System.out.println( err1.getMessage( ) );
     }*/


     // draw ink trail from previous point to current point

 // }
}

public void mouseReleased(MouseEvent me) {
}

 public void mouseMoved(MouseEvent me) {
 }





class PaintPanel extends JPanel
{

private Vector<Line2D.Double> v;
 private final Stroke INK_STROKE = new BasicStroke(5.0f,
        BasicStroke.CAP_ROUND, BasicStroke.JOIN_ROUND);

PaintPanel()
{
   v = new Vector<Line2D.Double>();

this.setBackground(Color.white);

}
@Override
  public void paintComponent(Graphics gd) {

    super.paintComponent(gd);
paintImage(gd);



}


 public void paintImage(Graphics gd){
     Graphics2D g2 = (Graphics2D)gd;
    //Rectangle aa = new Rectangle( 10, 10, 100, 100);
     //g2.draw(aa);
     g2.setColor(Color.red);
     Stroke s = g2.getStroke(); // save current stroke
     g2.setStroke(INK_STROKE);

     for (int i = 0; i < v.size(); ++i)
     g2.draw((Line2D.Double)v.elementAt(i));

     g2.setStroke(s);
     repaint();
}

 public void drawInk(int x1, int y1, int x2, int y2)
  {
     // get graphics context
     Graphics2D g2 = (Graphics2D)this.getGraphics();
     //System.out.println("dn " + g2 + "method was called");
     // create the line
     Line2D.Double inkSegment = new Line2D.Double(x1, y1, x2, y2);

     g2.setColor(Color.red);    // set the inking color
     Stroke s = g2.getStroke(); // save current stroke
     g2.setStroke(INK_STROKE);  // set desired stroke 
     g2.draw(inkSegment);       // draw it!   
     g2.setStroke(s);           // restore stroke 
     v.add(inkSegment);         // add to vector
    repaint();
  }
 }

}

2 个答案:

答案 0 :(得分：1)

stroke[sampleCount]

我没有看到要分配var stroke，所以这可能是你的空指针异常。

答案 1 :(得分：0)

您尝试使用stroke，但您从未初始化它。用新数组初始化!!

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