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这也是我们java老师给我们的thinking in java的一些资料

      <font color=#004488>"#4: 5"</font>,
      <font color=#004488>"#5: 5"</font>,
      <font color=#004488>"#3: 5"</font>,
      <font color=#004488>"#1: 4"</font>,
      <font color=#004488>"#2: 4"</font>,
      <font color=#004488>"#4: 4"</font>,
      <font color=#004488>"#5: 4"</font>,
      <font color=#004488>"#3: 4"</font>,
      <font color=#004488>"#1: 3"</font>,
      <font color=#004488>"#2: 3"</font>,
      <font color=#004488>"#4: 3"</font>,
      <font color=#004488>"#5: 3"</font>,
      <font color=#004488>"#3: 3"</font>,
      <font color=#004488>"#1: 2"</font>,
      <font color=#004488>"#2: 2"</font>,
      <font color=#004488>"#4: 2"</font>,
      <font color=#004488>"#5: 2"</font>,
      <font color=#004488>"#3: 2"</font>,
      <font color=#004488>"#1: 1"</font>,
      <font color=#004488>"#2: 1"</font>,
      <font color=#004488>"#4: 1"</font>,
      <font color=#004488>"#5: 1"</font>,
      <font color=#004488>"#3: 1"</font>
    }, Test.IGNORE_ORDER + Test.WAIT);
  }
} <font color=#009900>///:~</font></PRE></FONT></BLOCKQUOTE><p><br></p>
<p>By using <b>yield(&#160;)</b>, the output is evened up quite a bit. But note that if the output string is longer, you will see output that is roughly the same as it was in <b>SimpleThread.java</b> (try it&#151;change <b>toString(&#160;)</b> to put out longer and longer strings to see what happens). Since the scheduling mechanism is <i>preemptive</i>, it decides to interrupt a thread and switch to another whenever it wants, so if I/O (which is executed via the <b>main(&#160;) </b>thread) takes too long, it is interrupted before <b>run(&#160;)</b> has a chance to <b>yield(&#160;)</b>. In general, <b>yield(&#160;) </b>is useful only in rare situations, and you can&#146;t rely on it to do any serious tuning of your application. <font size="-2"><a href="mailto:[e-mail]?Subject=[TIJ3]A0178" title="Send BackTalk Comment">Feedback</a></font><br></p>
<h3>
<a name="_Toc24775839"></a><a name="Heading16971"></a>Sleeping</h3>
<p>Another way you can control the behavior of your threads is by calling <b>sleep(&#160;)</b> to cease execution for a given number of milliseconds. In the preceding example, if you replace the call to <b>yield(&#160;)</b> with a call to <a name="Index1537"></a><b>sleep(&#160;)</b>, you get the following: <font size="-2"><a href="mailto:[e-mail]?Subject=[TIJ3]A0179" title="Send BackTalk Comment">Feedback</a></font><br></p>

<BLOCKQUOTE><FONT SIZE = "+1"><PRE><font color=#009900>//: c13:SleepingThread.java</font>
<font color=#009900>// Calling sleep() to wait for awhile.</font>
<font color=#0000ff>import</font> com.bruceeckel.simpletest.*;

<font color=#0000ff>public</font> <font color=#0000ff>class</font> SleepingThread <font color=#0000ff>extends</font> Thread {
  <font color=#0000ff>private</font> <font color=#0000ff>static</font> Test monitor = <font color=#0000ff>new</font> Test();
  <font color=#0000ff>private</font> <font color=#0000ff>int</font> countDown = 5;
  <font color=#0000ff>private</font> <font color=#0000ff>static</font> <font color=#0000ff>int</font> threadCount = 0;
  <font color=#0000ff>public</font> SleepingThread() {
    <font color=#0000ff>super</font>(<font color=#004488>""</font> + ++threadCount);
    start();
  }
  <font color=#0000ff>public</font> String toString() {
    <font color=#0000ff>return</font> <font color=#004488>"#"</font> + getName() + <font color=#004488>": "</font> + countDown;
  }
  <font color=#0000ff>public</font> <font color=#0000ff>void</font> run() {
    <font color=#0000ff>while</font>(<font color=#0000ff>true</font>) {
      System.out.println(<font color=#0000ff>this</font>);
      <font color=#0000ff>if</font>(--countDown == 0) <font color=#0000ff>return</font>;
      <font color=#0000ff>try</font> {
        sleep(100);
      } <font color=#0000ff>catch</font> (InterruptedException e) {
        <font color=#0000ff>throw</font> <font color=#0000ff>new</font> RuntimeException(e);
      }
    }
  }
  <font color=#0000ff>public</font> <font color=#0000ff>static</font> <font color=#0000ff>void</font>
  main(String[] args) <font color=#0000ff>throws</font> InterruptedException {
    <font color=#0000ff>for</font>(<font color=#0000ff>int</font> i = 0; i &lt; 5; i++)
      <font color=#0000ff>new</font> SleepingThread().join();
    monitor.expect(<font color=#0000ff>new</font> String[] {
      <font color=#004488>"#1: 5"</font>,
      <font color=#004488>"#1: 4"</font>,
      <font color=#004488>"#1: 3"</font>,
      <font color=#004488>"#1: 2"</font>,
      <font color=#004488>"#1: 1"</font>,
      <font color=#004488>"#2: 5"</font>,
      <font color=#004488>"#2: 4"</font>,
      <font color=#004488>"#2: 3"</font>,
      <font color=#004488>"#2: 2"</font>,
      <font color=#004488>"#2: 1"</font>,
      <font color=#004488>"#3: 5"</font>,
      <font color=#004488>"#3: 4"</font>,
      <font color=#004488>"#3: 3"</font>,
      <font color=#004488>"#3: 2"</font>,
      <font color=#004488>"#3: 1"</font>,
      <font color=#004488>"#4: 5"</font>,
      <font color=#004488>"#4: 4"</font>,
      <font color=#004488>"#4: 3"</font>,
      <font color=#004488>"#4: 2"</font>,
      <font color=#004488>"#4: 1"</font>,
      <font color=#004488>"#5: 5"</font>,
      <font color=#004488>"#5: 4"</font>,
      <font color=#004488>"#5: 3"</font>,
      <font color=#004488>"#5: 2"</font>,
      <font color=#004488>"#5: 1"</font>
    });
  }
} <font color=#009900>///:~</font></PRE></FONT></BLOCKQUOTE><p><br></p>
<p>When you call <b>sleep(&#160;)</b>, it must be placed inside a <b>try</b> block because it&#146;s possible for <b>sleep(&#160;)</b> to be interrupted before it times out. This happens if someone else has a reference to the thread and they call <b>interrupt(&#160;)</b> on the thread (<a name="Index1538"></a><b>interrupt(&#160;)</b> also affects the thread if <b>wait(&#160;)</b> or <b>join(&#160;)</b> has been called for it, so those calls must be in a similar <b>try</b> block&#151;you&#146;ll learn about those methods later). Usually, if you&#146;re going to break out of a suspended thread using <b>interrupt(&#160;)</b> you will use <b>wait(&#160;)</b> rather than <b>sleep(&#160;)</b>, so that ending up inside the <b>catch</b> clause is unlikely. Here, we follow the maxim &#147;don&#146;t catch an exception unless you know what to do with it&#148; by re-throwing it as a <b>RuntimeException</b>. <font size="-2"><a href="mailto:[e-mail]?Subject=[TIJ3]A0175" title="Send BackTalk Comment">Feedback</a></font><br></p>
<p>You&#146;ll notice that the output is deterministic&#151;each thread counts down before the next one starts. This is because <b>join(&#160;)</b> (which you&#146;ll learn about shortly) is used on each thread, so that <b>main(&#160;)</b> waits for the thread to complete before continuing. If you did not use <b>join(&#160;)</b>, you&#146;d see that the threads tend to run in any order, which means that <b>sleep(&#160;)</b> is also not a way for you to control the order of thread execution. It just stops the execution of the thread for awhile. The only guarantee that you have is that the thread will sleep at least 100 milliseconds, but it may take longer before the thread resumes execution, because the thread scheduler still has to get back to it after the sleep interval expires. <font size="-2"><a href="mailto:[e-mail]?Subject=[TIJ3]Chap14_2207" title="Send BackTalk Comment">Feedback</a></font><br></p>
<p>If you must control the order of execution of threads, your best bet is not to use threads at all, but instead to write your own cooperative routines that hand control to each other in a specified order. <font size="-2"><a href="mailto:[e-mail]?Subject=[TIJ3]A0174" title="Send BackTalk Comment">Feedback</a></font><br></p>
<h3>
<a name="_Toc24775840"></a><a name="Heading17036"></a>Priority</h3>
<p>The <a name="Index1539"></a><a name="Index1540"></a><i>priority</i> of a thread tells the scheduler how important this thread is. Although the order that the CPU attends to an existing set of threads is indeterminate, if there are a number of threads blocked and waiting to be run, the scheduler will lean toward the one with the highest priority first. However, this doesn&#146;t mean that threads with lower priority aren&#146;t run (that is, you can&#146;t get deadlocked because of priorities). Lower priority threads just tend to run less often. <font size="-2"><a href="mailto:[e-mail]?Subject=[TIJ3]Chap14_2306" title="Send BackTalk Comment">Feedback</a></font><br></p>
<p>Here&#146;s <b>SimpleThread.java</b> modified so that the priority levels are demonstrated. The priorities are adjusting by using <b>Thread</b>&#146;s <b>setPriority(&#160;)</b> method.<br></p>

<BLOCKQUOTE><FONT SIZE = "+1"><PRE><font color=#009900>//: c13:SimplePriorities.java</font>
<font color=#009900>// Shows the use of thread priorities.</font>
<font color=#0000ff>import</font> com.bruceeckel.simpletest.*;

<font color=#0000ff>public</font> <font color=#0000ff>class</font> SimplePriorities <font color=#0000ff>extends</font> Thread {
  <font color=#0000ff>private</font> <font color=#0000ff>static</font> Test monitor = <font color=#0000ff>new</font> Test();
  <font color=#0000ff>private</font> <font color=#0000ff>int</font> countDown = 5;
  <font color=#0000ff>private</font> <font color=#0000ff>volatile</font> <font color=#0000ff>double</font> d = 0; <font color=#009900>// No optimization</font>
  <font color=#0000ff>public</font> SimplePriorities(<font color=#0000ff>int</font> priority) {
    setPriority(priority);
    start();
  }
  <font color=#0000ff>public</font> String toString() {
    <font color=#0000ff>return</font> <font color=#0000ff>super</font>.toString() + <font color=#004488>": "</font> + countDown;
  }
  <font color=#0000ff>public</font> <font color=#0000ff>void</font> run() {
    <font color=#0000ff>while</font>(<font color=#0000ff>true</font>) {
      <font color=#009900>// An expensive, interruptable operation:</font>
      <font color=#0000ff>for</font>(<font color=#0000ff>int</font> i = 1; i &lt; 100000; i++)
        d = d + (Math.PI + Math.E) / (<font color=#0000ff>double</font>)i;
      System.out.println(<font color=#0000ff>this</font>);
      <font color=#0000ff>if</font>(--countDown == 0) <font color=#0000ff>return</font>;
    }
  }
  <font color=#0000ff>public</font> <font color=#0000ff>static</font> <font color=#0000ff>void</font> main(String[] args) {
    <font color=#0000ff>new</font> SimplePriorities(Thread.MAX_PRIORITY);
    <font color=#0000ff>for</font>(<font color=#0000ff>int</font> i = 0; i &lt; 5; i++)
      <font color=#0000ff>new</font> SimplePriorities(Thread.MIN_PRIORITY);
    monitor.expect(<font color=#0000ff>new</font> String[] {
      <font color=#004488>"Thread[Thread-1,10,main]: 5"</font>,
      <font color=#004488>"Thread[Thread-1,10,main]: 4"</font>,
      <font color=#004488>"Thread[Thread-1,10,main]: 3"</font>,
      <font color=#004488>"Thread[Thread-1,10,main]: 2"</font>,
      <font color=#004488>"Thread[Thread-1,10,main]: 1"</font>,
      <font color=#004488>"Thread[Thread-2,1,main]: 5"</font>,
      <font color=#004488>"Thread[Thread-2,1,main]: 4"</font>,
      <font color=#004488>"Thread[Thread-2,1,main]: 3"</font>,
      <font color=#004488>"Thread[Thread-2,1,main]: 2"</font>,
      <font color=#004488>"Thread[Thread-2,1,main]: 1"</font>,
      <font color=#004488>"Thread[Thread-3,1,main]: 5"</font>,
      <font color=#004488>"Thread[Thread-4,1,main]: 5"</font>,
      <font color=#004488>"Thread[Thread-5,1,main]: 5"</font>,
      <font color=#004488>"Thread[Thread-6,1,main]: 5"</font>,
      <font color=#004488>"Thread[Thread-3,1,main]: 4"</font>,