tij0157.html

学习java的经典书籍

following portion of the example, the two classes work with generic <A NAME="Index2563"></A></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Reader</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
and <A NAME="Index2564"></A></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Writer</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
objects (using the Java 1.1<A NAME="Index2565"></A>
Streams), but in the test framework a <A NAME="Index2566"></A><A NAME="Index2567"></A>piped
stream will be set up to allow the two threads to safely pass data to each
other (which is the purpose of piped streams).
</FONT><P></DIV><DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">The
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Sender</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
puts data into the 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Writer</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
and sleeps for a random amount of time. However, 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Receiver</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
has no 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>sleep(&#160;)</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">,
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>suspend(&#160;)</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">,
or 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>wait(&#160;)</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">.
But when it does a 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>read(&#160;)</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
it automatically blocks when there is no more data.
</FONT><P></DIV>

<font color="#990000"><PRE><font color="#009900">///:Continuing</font>
<font color="#0000ff">class</font> Sender <font color="#0000ff">extends</font> Blockable { <font color="#009900">// send</font>
  <font color="#0000ff">private</font> Writer out;
  <font color="#0000ff">public</font> Sender(Container c, Writer out) { 
    <font color="#0000ff">super</font>(c);
    <font color="#0000ff">this</font>.out = out; 
  }
  <font color="#0000ff">public</font> <font color="#0000ff">void</font> run() {
    <font color="#0000ff">while</font>(<font color="#0000ff">true</font>) {
      <font color="#0000ff">for</font>(<font color="#0000ff">char</font> c = 'A'; c &lt;= 'z'; c++) {
         <font color="#0000ff">try</font> {
          i++;
          out.write(c);
          state.setText("Sender sent: " 
            + (<font color="#0000ff">char</font>)c);
          sleep((<font color="#0000ff">int</font>)(3000 * Math.random()));
        } <font color="#0000ff">catch</font> (InterruptedException e){}
          <font color="#0000ff">catch</font> (IOException e) {}
      }
    }
  }
}

<font color="#0000ff">class</font> Receiver <font color="#0000ff">extends</font> Blockable {
  <font color="#0000ff">private</font> Reader in;
  <font color="#0000ff">public</font> Receiver(Container c, Reader in) { 
    <font color="#0000ff">super</font>(c);
    <font color="#0000ff">this</font>.in = in; 
  }
  <font color="#0000ff">public</font> <font color="#0000ff">void</font> run() {
    <font color="#0000ff">try</font> {
      <font color="#0000ff">while</font>(<font color="#0000ff">true</font>) {
        i++; <font color="#009900">// Show peeker it's alive</font>
        <font color="#009900">// Blocks until characters are there:</font>
        state.setText("Receiver read: "
          + (<font color="#0000ff">char</font>)in.read());
      }
    } <font color="#0000ff">catch</font>(IOException e) { e.printStackTrace();}
  }
} <font color="#009900">///:Continued </PRE></font></font><DIV ALIGN=LEFT><P></DIV><DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">Both
classes also put information into their 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>state</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
fields and change 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>i
</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">so
the 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Peeker</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
can see that the thread is running.
</FONT><P></DIV>
<A NAME="Heading501"></A><H4 ALIGN=LEFT>
Testing</H4>
<DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">The
main applet class is surprisingly simple because most of the work has been put
into the 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Blockable</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
framework. Basically, an array of 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Blockable</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
objects is created, and since each one is a thread, they perform their own
activities when you press the &#8220;start&#8221; button. There&#8217;s also a
button and 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>actionPerformed(&#160;)</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
clause to stop all of the 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Peeker</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
objects, which provides a demonstration of the alternative to the deprecated
(in Java 1.2<A NAME="Index2568"></A>)
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>stop(&#160;)</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
method of 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Thread</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">.</FONT><P></DIV><DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">To
set up a connection between the 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Sender</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
and 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Receiver</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
objects, a 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>PipedWriter</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
and 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>PipedReader</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
are created. Note that the 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>PipedReader</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>in
</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">must
be connected to the 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>PipedWriter</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>out
</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">via
a constructor argument. After that, anything that&#8217;s placed in 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>out</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
can later be extracted from 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>in</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">,
as if it passed through a pipe (hence the name). The 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>in</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
and 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>out</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
objects are then passed to the 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Receiver</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
and 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Sender</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
constructors, respectively, which treat them as 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Reader</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
and 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Writer
</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">objects
of any type (that is, they are upcast).
</FONT><P></DIV><DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">The
array of 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Blockable</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
handles 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>b</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
is not initialized at its point of definition because the piped streams cannot
be set up before that definition takes place (the need for the 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>try</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
block prevents this). 
</FONT><P></DIV>

<font color="#990000"><PRE><font color="#009900">///:Continuing</font>
<font color="#009900">/////////// Testing Everything ///////////</font>
<font color="#0000ff">public</font> <font color="#0000ff">class</font> Blocking <font color="#0000ff">extends</font> Applet {
  <font color="#0000ff">private</font> Button 
    start = <font color="#0000ff">new</font> Button("Start"),
    stopPeekers = <font color="#0000ff">new</font> Button("Stop Peekers");
  <font color="#0000ff">private</font> <font color="#0000ff">boolean</font> started = <font color="#0000ff">false</font>;
  <font color="#0000ff">private</font> Blockable[] b;
  <font color="#0000ff">private</font> PipedWriter out;
  <font color="#0000ff">private</font> PipedReader in;
  <font color="#0000ff">public</font> <font color="#0000ff">void</font> init() {
     out = <font color="#0000ff">new</font> PipedWriter();
    <font color="#0000ff">try</font> {
      in = <font color="#0000ff">new</font> PipedReader(out);
    } <font color="#0000ff">catch</font>(IOException e) {}
    b = <font color="#0000ff">new</font> Blockable[] {
      <font color="#0000ff">new</font> Sleeper1(<font color="#0000ff">this</font>),
      <font color="#0000ff">new</font> Sleeper2(<font color="#0000ff">this</font>),
      <font color="#0000ff">new</font> SuspendResume1(<font color="#0000ff">this</font>),
      <font color="#0000ff">new</font> SuspendResume2(<font color="#0000ff">this</font>),
      <font color="#0000ff">new</font> WaitNotify1(<font color="#0000ff">this</font>),
      <font color="#0000ff">new</font> WaitNotify2(<font color="#0000ff">this</font>),
      <font color="#0000ff">new</font> Sender(<font color="#0000ff">this</font>, out),
      <font color="#0000ff">new</font> Receiver(<font color="#0000ff">this</font>, in)
    };
    start.addActionListener(<font color="#0000ff">new</font> StartL());
    add(start);
    stopPeekers.addActionListener(
      <font color="#0000ff">new</font> StopPeekersL());
    add(stopPeekers);
  }
  <font color="#0000ff">class</font> StartL <font color="#0000ff">implements</font> ActionListener {
    <font color="#0000ff">public</font> <font color="#0000ff">void</font> actionPerformed(ActionEvent e) {
      <font color="#0000ff">if</font>(!started) {
        started = <font color="#0000ff">true</font>;
        <font color="#0000ff">for</font>(<font color="#0000ff">int</font> i = 0; i &lt; b.length; i++)
          b[i].start();
      }
    }
  }
  <font color="#0000ff">class</font> StopPeekersL <font color="#0000ff">implements</font> ActionListener {
    <font color="#0000ff">public</font> <font color="#0000ff">void</font> actionPerformed(ActionEvent e) {
      <font color="#009900">// Demonstration of the preferred </font>
      <font color="#009900">// alternative to Thread.stop():</font>
      <font color="#0000ff">for</font>(<font color="#0000ff">int</font> i = 0; i &lt; b.length; i++)
        b[i].stopPeeker();
    }
  }
  <font color="#0000ff">public</font> <font color="#0000ff">static</font> <font color="#0000ff">void</font> main(String[] args) {
    Blocking applet = <font color="#0000ff">new</font> Blocking();
    Frame aFrame = <font color="#0000ff">new</font> Frame("Blocking");
    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(applet, BorderLayout.CENTER);
    aFrame.setSize(350,550);
    applet.init();