tij0127.html

学习java的经典书籍

</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><I>their</I></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
handles, and so on. This is quite a commitment. It effectively means that for a
deep copy to work you must either control all of the code in all of the
classes, or at least have enough knowledge about all of the classes involved in
the deep copy to know that they are performing their own deep copy correctly.
</FONT><P></DIV><DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">This
example shows what you must do to accomplish a deep copy when dealing with a
composed object:
</FONT><P></DIV>

<font color="#990000"><PRE><font color="#009900">//: DeepCopy.java</font>
<font color="#009900">// Cloning a composed object</font>

<font color="#0000ff">class</font> DepthReading <font color="#0000ff">implements</font> Cloneable {
  <font color="#0000ff">private</font> <font color="#0000ff">double</font> depth;
  <font color="#0000ff">public</font> DepthReading(<font color="#0000ff">double</font> depth) { 
    <font color="#0000ff">this</font>.depth = depth;
  }
  <font color="#0000ff">public</font> Object clone() {
    Object o = <font color="#0000ff">null</font>;
    <font color="#0000ff">try</font> {
      o = <font color="#0000ff">super</font>.clone();
    } <font color="#0000ff">catch</font> (CloneNotSupportedException e) {
      e.printStackTrace();
    }
    <font color="#0000ff">return</font> o;
  }
}

<font color="#0000ff">class</font> TemperatureReading <font color="#0000ff">implements</font> Cloneable {
  <font color="#0000ff">private</font> <font color="#0000ff">long</font> time;
  <font color="#0000ff">private</font> <font color="#0000ff">double</font> temperature;
  <font color="#0000ff">public</font> TemperatureReading(<font color="#0000ff">double</font> temperature) {
    time = System.currentTimeMillis();
    <font color="#0000ff">this</font>.temperature = temperature;
  }
  <font color="#0000ff">public</font> Object clone() {
    Object o = <font color="#0000ff">null</font>;
    <font color="#0000ff">try</font> {
      o = <font color="#0000ff">super</font>.clone();
    } <font color="#0000ff">catch</font> (CloneNotSupportedException e) {
      e.printStackTrace();
    }
    <font color="#0000ff">return</font> o;
  }
}

<font color="#0000ff">class</font> OceanReading <font color="#0000ff">implements</font> Cloneable {
  <font color="#0000ff">private</font> DepthReading depth;
  <font color="#0000ff">private</font> TemperatureReading temperature;
  <font color="#0000ff">public</font> OceanReading(<font color="#0000ff">double</font> tdata, <font color="#0000ff">double</font> ddata){
    temperature = <font color="#0000ff">new</font> TemperatureReading(tdata);
    depth = <font color="#0000ff">new</font> DepthReading(ddata);
  }
  <font color="#0000ff">public</font> Object clone() {
    OceanReading o = <font color="#0000ff">null</font>;
    <font color="#0000ff">try</font> {
      o = (OceanReading)<font color="#0000ff">super</font>.clone();
    } <font color="#0000ff">catch</font> (CloneNotSupportedException e) {
      e.printStackTrace();
    }
    <font color="#009900">// Must clone handles:</font>
    o.depth = (DepthReading)o.depth.clone();
    o.temperature = 
      (TemperatureReading)o.temperature.clone();
    <font color="#0000ff">return</font> o; <font color="#009900">// Upcasts back to Object</font>
  }
}

<font color="#0000ff">public</font> <font color="#0000ff">class</font> DeepCopy {
  <font color="#0000ff">public</font> <font color="#0000ff">static</font> <font color="#0000ff">void</font> main(String[] args) {
    OceanReading reading = 
      <font color="#0000ff">new</font> OceanReading(33.9, 100.5);
    <font color="#009900">// Now clone it:</font>
    OceanReading r = 
      (OceanReading)reading.clone();
  }
} <font color="#009900">///:~ </PRE></font></font><DIV ALIGN=LEFT><P></DIV><DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>DepthReading</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
and 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>TemperatureReading</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
are quite similar; they both contain only primitives. Therefore, the 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>clone(&#160;)</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
method can be quite simple: it calls 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>super.clone(&#160;)</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
and returns the result. Note that the 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>clone(&#160;)</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
code for both classes is identical.
</FONT><P></DIV><DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>OceanReading</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
is composed of 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>DepthReading</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
and 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>TemperatureReading</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
objects and so, to produce a deep copy, its 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>clone(&#160;)</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
must clone the handles inside 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>OceanReading</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">.
To accomplish this, the result of 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>super.clone(&#160;)</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
must be cast to an 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>OceanReading</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
object (so you can access the 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>depth</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
and 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>temperature</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
handles).
</FONT><a name="_Toc408018663"></a><P></DIV>
<A NAME="Heading376"></A><H3 ALIGN=LEFT>
A
deep copy with Vector
</H3>
<DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">Let&#8217;s
revisit the <A NAME="Index1476"></A><A NAME="Index1477"></A></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Vector</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
example from earlier in this chapter. This time the 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Int2</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
class is cloneable so the 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Vector</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
can be deep copied:
</FONT><P></DIV>

<font color="#990000"><PRE><font color="#009900">//: AddingClone.java</font>
<font color="#009900">// You must go through a few gyrations to</font>
<font color="#009900">// add cloning to your own class.</font>
<font color="#0000ff">import</font> java.util.*;

<font color="#0000ff">class</font> Int2 <font color="#0000ff">implements</font> Cloneable {
  <font color="#0000ff">private</font> <font color="#0000ff">int</font> i;
  <font color="#0000ff">public</font> Int2(<font color="#0000ff">int</font> ii) { i = ii; }
  <font color="#0000ff">public</font> <font color="#0000ff">void</font> increment() { i++; }
  <font color="#0000ff">public</font> String toString() {
    <font color="#0000ff">return</font> Integer.toString(i);
  }
  <font color="#0000ff">public</font> Object clone() {
    Object o = <font color="#0000ff">null</font>;
    <font color="#0000ff">try</font> {
      o = <font color="#0000ff">super</font>.clone();
    } <font color="#0000ff">catch</font> (CloneNotSupportedException e) {
      System.out.println("Int2 can't clone");
    }
    <font color="#0000ff">return</font> o;
  }
}

<font color="#009900">// Once it's cloneable, inheritance</font>
<font color="#009900">// doesn't remove cloneability:</font>
<font color="#0000ff">class</font> Int3 <font color="#0000ff">extends</font> Int2 {
  <font color="#0000ff">private</font> <font color="#0000ff">int</font> j; <font color="#009900">// Automatically duplicated</font>
  <font color="#0000ff">public</font> Int3(<font color="#0000ff">int</font> i) { <font color="#0000ff">super</font>(i); }
}

<font color="#0000ff">public</font> <font color="#0000ff">class</font> AddingClone {
  <font color="#0000ff">public</font> <font color="#0000ff">static</font> <font color="#0000ff">void</font> main(String[] args) {
    Int2 x = <font color="#0000ff">new</font> Int2(10);
    Int2 x2 = (Int2)x.clone();
    x2.increment();
    System.out.println(
      "x = " + x + ", x2 = " + x2);
    <font color="#009900">// Anything inherited is also cloneable:</font>
    Int3 x3 = <font color="#0000ff">new</font> Int3(7);
    x3 = (Int3)x3.clone();

    Vector v = <font color="#0000ff">new</font> Vector();
    <font color="#0000ff">for</font>(<font color="#0000ff">int</font> i = 0; i &lt; 10; i++ )
      v.addElement(<font color="#0000ff">new</font> Int2(i));
    System.out.println("v: " + v);
    Vector v2 = (Vector)v.clone();
    <font color="#009900">// Now clone each element:</font>
    <font color="#0000ff">for</font>(<font color="#0000ff">int</font> i = 0; i &lt; v.size(); i++)
      v2.setElementAt(
        ((Int2)v2.elementAt(i)).clone(), i);
    <font color="#009900">// Increment all v2's elements:</font>
    <font color="#0000ff">for</font>(Enumeration e = v2.elements();
        e.hasMoreElements(); )
      ((Int2)e.nextElement()).increment();
    <font color="#009900">// See if it changed v's elements:</font>
    System.out.println("v: " + v);
    System.out.println("v2: " + v2);
  }
} <font color="#009900">///:~ </PRE></font></font><DIV ALIGN=LEFT><P></DIV><DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Int3</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
is inherited from 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Int2</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
and a new primitive member 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>int
j 
</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">is
added. You might think that you&#8217;d need to override 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>clone(&#160;)</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
again to make sure 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>j</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
is copied, but that&#8217;s not the case. When 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Int2</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">&#8217;s
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>clone(&#160;)</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
is called as 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Int3</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">&#8217;s
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>clone(&#160;)</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">,
it calls 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Object.clone(&#160;),</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
which determines that it&#8217;s working with an 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Int3</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
and duplicates all the bits in the 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Int3</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">.
As long as you don&#8217;t add handles that need to be cloned, the one call to 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Object.clone(&#160;)</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
performs all of the necessary duplication, regardless of how far down in the
hierarchy 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>clone(&#160;)</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
is defined.
</FONT><P></DIV><DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">You