tij0150.html

学习java的经典书籍

<font color="#0000ff">public</font> <font color="#0000ff">void</font> croak()
<font color="#0000ff">public</font> <font color="#0000ff">void</font> removeActionListener(ActionListener)
<font color="#0000ff">public</font> <font color="#0000ff">void</font> addActionListener(ActionListener)
<font color="#0000ff">public</font> <font color="#0000ff">int</font> getJumps()
<font color="#0000ff">public</font> <font color="#0000ff">void</font> setColor(Color)
<font color="#0000ff">public</font> <font color="#0000ff">void</font> setSpots(Spots)
<font color="#0000ff">public</font> <font color="#0000ff">void</font> setJumper(<font color="#0000ff">boolean</font>)
<font color="#0000ff">public</font> <font color="#0000ff">boolean</font> isJumper()
<font color="#0000ff">public</font> <font color="#0000ff">void</font> addKeyListener(KeyListener)
<font color="#0000ff">public</font> Color getColor()
<font color="#0000ff">public</font> <font color="#0000ff">void</font> removeKeyListener(KeyListener)
<font color="#0000ff">public</font> Spots getSpots()
======================
Event support:
Listener type:
  KeyListener
Listener method:
  keyTyped
Listener method:
  keyPressed
Listener method:
  keyReleased
Method descriptor:
  <font color="#0000ff">public</font> <font color="#0000ff">void</font> keyTyped(KeyEvent)
Method descriptor:
  <font color="#0000ff">public</font> <font color="#0000ff">void</font> keyPressed(KeyEvent)
Method descriptor:
  <font color="#0000ff">public</font> <font color="#0000ff">void</font> keyReleased(KeyEvent)
Add Listener Method:
  <font color="#0000ff">public</font> <font color="#0000ff">void</font> addKeyListener(KeyListener)
Remove Listener Method:
  <font color="#0000ff">public</font> <font color="#0000ff">void</font> removeKeyListener(KeyListener)
====================
Listener type:
  ActionListener
Listener method:
  actionPerformed
Method descriptor:
  <font color="#0000ff">public</font> <font color="#0000ff">void</font> actionPerformed(ActionEvent)
Add Listener Method:
  <font color="#0000ff">public</font> <font color="#0000ff">void</font> addActionListener(ActionListener)
Remove Listener Method:
  <font color="#0000ff">public</font> <font color="#0000ff">void</font> removeActionListener(ActionListener)
====================</PRE></font><DIV ALIGN=LEFT><P></DIV><DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">This
reveals most of what the 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Introspector</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
sees as it produces a 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>BeanInfo</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
object from your Bean. You can see that the type of the property and its name
are independent. Notice the lowercasing of the property name. (The only time
this doesn&#8217;t occur is when the property name begins with more than one
capital letter in a row.) And remember that the method names you&#8217;re
seeing here (such as the read and write methods) are actually produced from a 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Method</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
object that can be used to invoke the associated method on the object.
</FONT><P></DIV><DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">The
public method list includes the methods that are not associated with a property
or event, such as 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>croak(&#160;)</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">,
as well as those that are. These are all the methods that you can call
programmatically for a Bean, and the application builder tool can choose to
list all of these while you&#8217;re making method calls, to ease your task.
</FONT><P></DIV><DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">Finally,
you can see that the events are fully parsed out into the listener, its
methods, and the add- and remove-listener methods. Basically, once you have the 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>BeanInfo</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">,
you can find out everything of importance for the Bean. You can also call the
methods for that Bean, even though you don&#8217;t have any other information
except the object (again, a feature of reflection).
</FONT><a name="_Toc408018720"></a><P></DIV>
<A NAME="Heading457"></A><H3 ALIGN=LEFT>
A
more sophisticated Bean
</H3>
<DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">This
next example is slightly more sophisticated, albeit frivolous. It&#8217;s a
canvas that draws a little circle around the mouse whenever the mouse is moved.
When you press the mouse, the word &#8220;Bang!&#8221; appears in the middle of
the screen, and an action listener is fired.
</FONT><P></DIV><DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">The
properties you can change are the size of the circle as well as the color,
size, and text of the word that is displayed when you press the mouse. A 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>BangBean</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
also has its own <A NAME="Index2233"></A><A NAME="Index2234"></A></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>addActionListener(&#160;)</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
and <A NAME="Index2235"></A><A NAME="Index2236"></A></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>removeActionListener(&#160;)</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
so you can attach your own listener that will be fired when the user clicks on
the 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>BangBean</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">.
You should be able to recognize the property and event support:
</FONT><P></DIV>

<font color="#990000"><PRE><font color="#009900">//: BangBean.java</font>
<font color="#009900">// A graphical Bean</font>
<font color="#0000ff">package</font> bangbean;
<font color="#0000ff">import</font> java.awt.*;
<font color="#0000ff">import</font> java.awt.event.*;
<font color="#0000ff">import</font> java.io.*;
<font color="#0000ff">import</font> java.util.*;

<font color="#0000ff">public</font> <font color="#0000ff">class</font> BangBean <font color="#0000ff">extends</font> Canvas
     <font color="#0000ff">implements</font> Serializable {
  <font color="#0000ff">protected</font> <font color="#0000ff">int</font> xm, ym;
  <font color="#0000ff">protected</font> <font color="#0000ff">int</font> cSize = 20; <font color="#009900">// Circle size</font>
  <font color="#0000ff">protected</font> String text = "Bang!";
  <font color="#0000ff">protected</font> <font color="#0000ff">int</font> fontSize = 48;
  <font color="#0000ff">protected</font> Color tColor = Color.red;
  <font color="#0000ff">protected</font> ActionListener actionListener;
  <font color="#0000ff">public</font> BangBean() {
    addMouseListener(<font color="#0000ff">new</font> ML());
    addMouseMotionListener(<font color="#0000ff">new</font> MML());
  }
  <font color="#0000ff">public</font> <font color="#0000ff">int</font> getCircleSize() { <font color="#0000ff">return</font> cSize; }
  <font color="#0000ff">public</font> <font color="#0000ff">void</font> setCircleSize(<font color="#0000ff">int</font> newSize) {
    cSize = newSize;
  }
  <font color="#0000ff">public</font> String getBangText() { <font color="#0000ff">return</font> text; }
  <font color="#0000ff">public</font> <font color="#0000ff">void</font> setBangText(String newText) {
    text = newText;
  }
  <font color="#0000ff">public</font> <font color="#0000ff">int</font> getFontSize() { <font color="#0000ff">return</font> fontSize; }
  <font color="#0000ff">public</font> <font color="#0000ff">void</font> setFontSize(<font color="#0000ff">int</font> newSize) {
    fontSize = newSize;
  }
  <font color="#0000ff">public</font> Color getTextColor() { <font color="#0000ff">return</font> tColor; }
  <font color="#0000ff">public</font> <font color="#0000ff">void</font> setTextColor(Color newColor) {
    tColor = newColor;
  }
  <font color="#0000ff">public</font> <font color="#0000ff">void</font> paint(Graphics g) {
    g.setColor(Color.black);
    g.drawOval(xm - cSize/2, ym - cSize/2, 
      cSize, cSize);
  }
  <font color="#009900">// This is a unicast listener, which is</font>
  <font color="#009900">// the simplest form of listener management:</font>
  <font color="#0000ff">public</font> <font color="#0000ff">void</font> addActionListener (
      ActionListener l) 
        <font color="#0000ff">throws</font> TooManyListenersException {
    <font color="#0000ff">if</font>(actionListener != <font color="#0000ff">null</font>)
      <font color="#0000ff">throw</font> <font color="#0000ff">new</font> TooManyListenersException();
    actionListener = l;
  }
  <font color="#0000ff">public</font> <font color="#0000ff">void</font> removeActionListener(
      ActionListener l) {
    actionListener = <font color="#0000ff">null</font>;
  }
  <font color="#0000ff">class</font> ML <font color="#0000ff">extends</font> MouseAdapter {
    <font color="#0000ff">public</font> <font color="#0000ff">void</font> mousePressed(MouseEvent e) {
      Graphics g = getGraphics();
      g.setColor(tColor);
      g.setFont(
        <font color="#0000ff">new</font> Font(
          "TimesRoman", Font.BOLD, fontSize));
      <font color="#0000ff">int</font> width = 
        g.getFontMetrics().stringWidth(text);
      g.drawString(text, 
        (getSize().width - width) /2,
        getSize().height/2);
      g.dispose();
      <font color="#009900">// Call the listener's method:</font>
      <font color="#0000ff">if</font>(actionListener != <font color="#0000ff">null</font>)
        actionListener.actionPerformed(
          <font color="#0000ff">new</font> ActionEvent(BangBean.<font color="#0000ff">this</font>,
            ActionEvent.ACTION_PERFORMED, <font color="#0000ff">null</font>));
    }
  }
  <font color="#0000ff">class</font> MML <font color="#0000ff">extends</font> MouseMotionAdapter {
    <font color="#0000ff">public</font> <font color="#0000ff">void</font> mouseMoved(MouseEvent e) {
      xm = e.getX();
      ym = e.getY();
      repaint();
    }
  }
  <font color="#0000ff">public</font> Dimension getPreferredSize() {
    <font color="#0000ff">return</font> <font color="#0000ff">new</font> Dimension(200, 200);
  }
  <font color="#009900">// Testing the BangBean:</font>
  <font color="#0000ff">public</font> <font color="#0000ff">static</font> <font color="#0000ff">void</font> main(String[] args) {
    BangBean bb = <font color="#0000ff">new</font> BangBean();
    <font color="#0000ff">try</font> {
      bb.addActionListener(<font color="#0000ff">new</font> BBL());
    } <font color="#0000ff">catch</font>(TooManyListenersException e) {}
    Frame aFrame = <font color="#0000ff">new</font> Frame("BangBean Test");
    aFrame.addWindowListener(
      <font color="#0000ff">new</font> WindowAdapter() {
        <font color="#0000ff">public</font> <font color="#0000ff">void</font> windowClosing(WindowEvent e) {
          System.exit(0);
        }
      });
    aFrame.add(bb, BorderLayout.CENTER);
    aFrame.setSize(300,300);
    aFrame.setVisible(<font color="#0000ff">true</font>);
  }
  <font color="#009900">// During testing, send action information</font>
  <font color="#009900">// to the console:</font>
  <font color="#0000ff">static</font> <font color="#0000ff">class</font> BBL <font color="#0000ff">implements</font> ActionListener {
    <font color="#0000ff">public</font> <font color="#0000ff">void</font> actionPerformed(ActionEvent e) {
      System.out.println("BangBean action");
    }
  }
} <font color="#009900">///:~ </PRE></font></font><DIV ALIGN=LEFT><P></DIV><DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">The
first thing you&#8217;ll notice is that 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>BangBean</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
implements the <A NAME="Index2237"></A><A NAME="Index2238"></A></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Serializable</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
interface. This means that the application builder tool can
&#8220;pickle&#8221; all the information for the 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>BangBean</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
using serialization after the program designer has adjusted the values of the
properties. When the Bean is created as part of the running application, these
&#8220;pickled&#8221; properties are restored so that you get exactly what you
designed.
</FONT><P></DIV><DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">You
can see that all the fields are 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>private</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">,
which is what you&#8217;ll usually do with a Bean &#8211; allow access only
through methods, usually using the &#8220;property&#8221; scheme.
</FONT><P></DIV><DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">When
you look at the signature for 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>addActionListener(&#160;)</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">,
you&#8217;ll see that it can throw a <A NAME="Index2239"></A><A NAME="Index2240"></A></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>TooManyListenersException</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">.
This indicates that it is <A NAME="Index2241"></A><A NAME="Index2242"></A></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><I>unicast</I></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">,
which means it notifies only one listener when the event occurs. Ordinarily,
you&#8217;ll use <A NAME="Index2243"></A><A NAME="Index2244"></A></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><I>multicast</I></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
events so that many listeners can be notified of an event. However, that runs
into issues that you won&#8217;t be ready for until the next chapter, so it
will be revisited there (under the heading &#8220;Java Beans revisited&#8221;).
A unicast event sidesteps the problem.
</FONT><P></DIV><DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">When
you press the mouse, the text is put in the middle of the 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>BangBean</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">,
and if the