sketchview.java

非常好的java事例以及带源码事例的java2教程

import javax.swing.*;
import java.util.*;                 // For Observer
import java.awt.*;
import java.awt.geom.*;
import java.awt.event.*;            // For events
import javax.swing.event.*;         // For mouse input adapter

class SketchView extends JComponent
                 implements Observer, Constants
{
  public SketchView(Sketcher theApp)
  {
    this.theApp = theApp;
    MouseHandler handler = new MouseHandler();         // create the mouse listener
    addMouseListener(handler);                         // Listen for button events
    addMouseMotionListener(handler);                   // Listen for motion events
  }

  public void paint(Graphics g)
  {
    Graphics2D g2D = (Graphics2D)g;                     // Get a 2D device context
    Iterator elements = theApp.getModel().getIterator();
    Element element;                                    // Stores an element

    while(elements.hasNext())                           // Go through the list
    {
      element = (Element)elements.next();               // Get the next element
      g2D.setPaint(element.getColor());                 // Set the element color
      g2D.draw(element.getShape());                     // Draw its shape
    }
  }

  // Method called by Observable object when it changes
  public void update(Observable o, Object rectangle)
  {
    if(rectangle == null)
      repaint();
    else
      repaint((Rectangle)rectangle);
  }

  class MouseHandler extends MouseInputAdapter
  {
    public void mousePressed(MouseEvent e)
    {
      start = e.getPoint();                              // Save cursor position
      int modifier = e.getModifiers();                   // Get modifiers

      if((modifier & e.BUTTON1_MASK) != 0)
      {
        g2D = (Graphics2D)getGraphics();                 // Get graphics context
        g2D.setXORMode(getBackground());                 // Set XOR mode
        g2D.setPaint(theApp.getWindow().getElementColor());   // Set color
      }
    }

    public void mouseDragged(MouseEvent e)
    {
      last = e.getPoint();                               // Save cursor position
      int modifier = e.getModifiers();                   // Get modifiers

      if((modifier & e.BUTTON1_MASK) != 0)
      {
        if(tempElement == null)                         // Is there an element?
          tempElement = createElement(start, last);     // No, so create one
        else
        {
          g2D.draw(tempElement.getShape());             // Yes - draw to erase it
          tempElement.modify(start, last);                     // Now modify it
        }
        g2D.draw(tempElement.getShape());               // and draw it
      }
    }

    public void mouseReleased(MouseEvent e)
    {
      int modifier = e.getModifiers();         // Get modifiers

      if((modifier & e.BUTTON1_MASK) != 0)
      {
        if(tempElement != null)
        {
          theApp.getModel().add(tempElement);  // Add element to the model
          tempElement = null;                  // No temporary stored
      }
        if(g2D != null)
        {
          g2D.dispose();                       // Release graphic context resource
          g2D = null;                          // Set it to null
        }
        start = last = null;                   // Remove the points
      }
    }

    private Element createElement(Point start, Point end)
    {
      switch(theApp.getWindow().getElementType())
      {
        case LINE:
           return new Element.Line(start, end,
                                   theApp.getWindow().getElementColor());
        
        case RECTANGLE:
           return new Element.Rectangle(start, end,
                                        theApp.getWindow().getElementColor());
        
        case CIRCLE:
           return new Element.Circle(start, end, 
                                     theApp.getWindow().getElementColor());

        case CURVE:
         return new Element.Curve(start, end,
                                  theApp.getWindow().getElementColor());
      }
      return null;
    }

    private Point start;                     // Stores cursor position on press
    private Point last;                      // Stores cursor position on drag
    private Element tempElement;             // Stores a temporary element
    private Graphics2D g2D;                  // Temporary graphics context
  }

  private Sketcher theApp;           // The application object
}