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学习java的经典书籍

        DataOutputStream out2 =
          <font color="#0000ff">new</font> DataOutputStream(
            <font color="#0000ff">new</font> BufferedOutputStream(
              <font color="#0000ff">new</font> FileOutputStream("Data.txt")));
        out2.writeDouble(3.14159);
        out2.writeBytes("That was pi");
        out2.close();
        DataInputStream in5 =
          <font color="#0000ff">new</font> DataInputStream(
            <font color="#0000ff">new</font> BufferedInputStream(
              <font color="#0000ff">new</font> FileInputStream("Data.txt")));
        BufferedReader in5br =
          <font color="#0000ff">new</font> BufferedReader(
            <font color="#0000ff">new</font> InputStreamReader(in5));
        <font color="#009900">// Must use DataInputStream for data:</font>
        System.out.println(in5.readDouble());
        <font color="#009900">// Can now use the "proper" readLine():</font>
        System.out.println(in5br.readLine());
      } <font color="#0000ff">catch</font>(EOFException e) {
        System.out.println("End of stream");
      }

      <font color="#009900">// 6. Reading and writing random access</font>
      <font color="#009900">// files is the same as before.</font>
      <font color="#009900">// (not repeated here)</font>

    } <font color="#0000ff">catch</font>(FileNotFoundException e) {
      System.out.println(
        "File Not Found:" + args[1]);
    } <font color="#0000ff">catch</font>(IOException e) {
      System.out.println("IO Exception");
    }
  }
} <font color="#009900">///:~ </PRE></font></font><DIV ALIGN=LEFT><P></DIV><DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">In
general, you&#8217;ll see that the conversion is fairly straightforward and the
code looks quite similar. There are some important differences, though. First
of all, since random access files have not changed, section 6 is not repeated.
</FONT><P></DIV><DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">Section
1 shrinks a bit because if all you&#8217;re doing is reading line input you
need only to wrap a 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>BufferedReader</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
around a 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>FileReader</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">.
Section 1b shows the new way to wrap <A NAME="Index1257"></A><A NAME="Index1258"></A></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>System.in</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
for reading <A NAME="Index1259"></A><A NAME="Index1260"></A><A NAME="Index1261"></A>console
input, and this expands because 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>System.in</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
is a 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>DataInputStream</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
and 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>BufferedReader</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
needs a 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>Reader</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
argument, so 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>InputStreamReader</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
is brought in to perform the translation.
</FONT><P></DIV><DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">In
section 2 you can see that if you have a 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>String</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
and want to read from it you just use a 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>StringReader</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
instead of a 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>StringBufferInputStream</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
and the rest of the code is identical.
</FONT><P></DIV><DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">Section
3 shows a bug in the design of the new IO stream library. If you have a 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>String</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
and you want to read from it, you&#8217;re 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><I>not</I></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
supposed to use a 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>StringBufferInputStream</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
any more. When you compile code involving a 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>StringBufferInputStream</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
constructor, you get a deprecation message telling you to not use it. Instead,
you&#8217;re supposed to use a 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>StringReader</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">.
However, if you want to do formatted memory input as in section 3, you&#8217;re
forced to use a 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>DataInputStream</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
&#8211; there is no &#8220;DataReader&#8221; to replace it &#8211; and a 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>DataInputStream</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
constructor requires an 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>InputStream</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
argument. So you have no choice but to use the deprecated 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>StringBufferInputStream</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
class. The compiler will give you a deprecation message but there&#8217;s
nothing you can do about it.
</FONT><A NAME="fnB48" HREF="#fn48">[48]</A><P></DIV><DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">Section
4 is a reasonably straightforward translation from the old streams to the new,
with no surprises. In section 5, you&#8217;re forced to use all the old streams
classes because 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>DataOutputStream</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
and 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>DataInputStream</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
require them and there are no alternatives. However, you don&#8217;t get any
deprecation messages at compile time. If a stream is deprecated, typically its
constructor produces a deprecation message to prevent you from using the entire
class, but in the case of 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>DataInputStream</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
only the 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>readLine(&#160;)</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
method is deprecated since you&#8217;re supposed to use a 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>BufferedReader</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
for 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>readLine(&#160;)</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
(but a 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>DataInputStream</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
for all other formatted input).
</FONT><P></DIV><DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">If
you compare section 5 with that section in 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>IOStreamDemo.java</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">,
you&#8217;ll notice that in 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><I>this</I></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
version, the data is written 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><I>before</I></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
the text. That&#8217;s because a bug was introduced in Java 1.1<A NAME="Index1262"></A>,
which is shown in the following code:
</FONT><P></DIV>

<font color="#990000"><PRE><font color="#009900">//: IOBug.java</font>
<font color="#009900">// Java 1.1 (and higher?) IO Bug</font>
<font color="#0000ff">import</font> java.io.*;

<font color="#0000ff">public</font> <font color="#0000ff">class</font> IOBug {
  <font color="#0000ff">public</font> <font color="#0000ff">static</font> <font color="#0000ff">void</font> main(String[] args) 
  <font color="#0000ff">throws</font> Exception {
    DataOutputStream out =
      <font color="#0000ff">new</font> DataOutputStream(
        <font color="#0000ff">new</font> BufferedOutputStream(
          <font color="#0000ff">new</font> FileOutputStream("Data.txt")));
    out.writeDouble(3.14159);
    out.writeBytes("That was the value of pi\n");
    out.writeBytes("This is pi/2:\n");
    out.writeDouble(3.14159/2);
    out.close();

    DataInputStream in =
      <font color="#0000ff">new</font> DataInputStream(
        <font color="#0000ff">new</font> BufferedInputStream(
          <font color="#0000ff">new</font> FileInputStream("Data.txt")));
    BufferedReader inbr =
      <font color="#0000ff">new</font> BufferedReader(
        <font color="#0000ff">new</font> InputStreamReader(in));
    <font color="#009900">// The doubles written BEFORE the line of text</font>
    <font color="#009900">// read back correctly:</font>
    System.out.println(in.readDouble());
    <font color="#009900">// Read the lines of text:</font>
    System.out.println(inbr.readLine());
    System.out.println(inbr.readLine());
    <font color="#009900">// Trying to read the doubles after the line</font>
    <font color="#009900">// produces an end-of-file exception:</font>
    System.out.println(in.readDouble());
  }
} <font color="#009900">///:~ </PRE></font></font><DIV ALIGN=LEFT><P></DIV><DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">It
appears that anything you write after a call to 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>writeBytes(&#160;)</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
is not recoverable. This is a rather limiting bug, and we can hope that it will
be fixed by the time you read this. You should run the above program to test
it; if you don&#8217;t get an exception and the values print correctly then
you&#8217;re out of the woods.
</FONT><a name="_Toc408018633"></a><P></DIV>
<A NAME="Heading338"></A><H3 ALIGN=LEFT>
Redirecting
standard IO
<P><A NAME="Index1263"></A><A NAME="Index1264"></A></H3>
<DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">Java
1.1<A NAME="Index1265"></A>
has added methods in class 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>System</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
that allow you to redirect the standard input, output, and error IO streams
using simple static method calls:
</FONT><P></DIV><DIV ALIGN=LEFT><A NAME="Index1266"></A><A NAME="Index1267"></A><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>setIn(InputStream)
</B></FONT><P><A NAME="Index1268"></A><A NAME="Index1269"></A><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>setOut(PrintStream)</B></FONT><P><A NAME="Index1270"></A><A NAME="Index1271"></A><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>setErr(PrintStream)
</B></FONT><P></DIV><DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">Redirecting
output is especially useful if you suddenly start creating a large amount of
output on your screen and it&#8217;s scrolling past faster than you can read
it. Redirecting input is valuable for a command-line program in which you want
to test a particular user-input sequence repeatedly. Here&#8217;s a simple
example that shows the use of these methods:
</FONT><P></DIV>

<font color="#990000"><PRE><font color="#009900">//: Redirecting.java</font>
<font color="#009900">// Demonstrates the use of redirection for </font>
<font color="#009900">// standard IO in Java 1.1</font>
<font color="#0000ff">import</font> java.io.*;

<font color="#0000ff">class</font> Redirecting {
  <font color="#0000ff">public</font> <font color="#0000ff">static</font> <font color="#0000ff">void</font> main(String[] args) {
    <font color="#0000ff">try</font> {
      BufferedInputStream in = 
        <font color="#0000ff">new</font> BufferedInputStream(
          <font color="#0000ff">new</font> FileInputStream(
            "Redirecting.java"));
      <font color="#009900">// Produces deprecation message:</font>
      PrintStream out =
        <font color="#0000ff">new</font> PrintStream(
          <font color="#0000ff">new</font> BufferedOutputStream(
            <font color="#0000ff">new</font> FileOutputStream("test.out")));
      System.setIn(in);
      System.setOut(out);
      System.setErr(out);

      BufferedReader br = 
        <font color="#0000ff">new</font> BufferedReader(
          <font color="#0000ff">new</font> InputStreamReader(System.in));
      String s;
      <font color="#0000ff">while</font>((s = br.readLine()) != <font color="#0000ff">null</font>)
        System.out.println(s);
      out.close(); <font color="#009900">// Remember this!</font>
    } <font color="#0000ff">catch</font>(IOException e) {
      e.printStackTrace();
    }
  }
} <font color="#009900">///:~ </PRE></font></font><DIV ALIGN=LEFT><P></DIV><DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">This
program attaches standard input to a file, and redirects standard output and
standard error to another file.
</FONT><P></DIV><DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">This
is another example in which a deprecation message is inevitable. The message
you can get when compiling with the 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>-deprecation
</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">flag
is: 
</FONT><P></DIV><DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><I>Note:
The constructor java.io.PrintStream(java.io.OutputStream) 
</I></FONT><P><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><I>has
been deprecated.
</I></FONT><P></DIV><DIV ALIGN=LEFT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">However,
both 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>System.setOut(&#160;)</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
and 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>System.setErr(&#160;)</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
require a 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>PrintStream</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
object as an argument, so you are forced to call the 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>PrintStream</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
constructor. You might wonder, if Java 1.1<A NAME="Index1272"></A>
deprecates the entire 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>PrintStream</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
class by deprecating the constructor, why the library designers, at the same
time as they added this deprecation, also add new methods to 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>System</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
that required a 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>PrintStream</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
rather than a 
</FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black"><B>PrintWriter,</B></FONT><FONT FACE="Carmina Md BT" SIZE=3 COLOR="Black">
which is the new and preferred replacement. It&#8217;s a mystery.
</FONT><a name="_Toc408018634"></a><P></DIV>
<HR><DIV ALIGN=LEFT><A NAME="fn48" HREF="#fnB48">[48]</A><FONT FACE="Carmina Md BT" SIZE=2 COLOR="Black">
Perhaps by the time you read this, the bug will be fixed.
</FONT><P></DIV>


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