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關于流

我一直對流都有點暈暈的，今天基本算搞清楚了所以然，所以在這里寫出，一來為了記憶，一來也希望能對和我一樣在這里有點模糊的一點幫助。（呵呵，不會就我一個人這么倒霉吧？）?

輸入流：此流對應于鍵盤輸入或者由主機環境或用戶指定的另一個輸入源

超類： InputStream (System.in 就屬于這類 )

輸出流：此流對應于顯示器輸出或者由主機環境或用戶指定的另一個輸出目標。

超類： OutputStream (System.out 就屬于這類。其實 System.err 也是間接屬于它 )

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一切都是流！

看一段程序

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?1 /**/ /*
?2 ?*?ThreadedEchoServer.java
?3 ?*
?4 ?*?Created?on?2006年10月14日,?上午11:57
?5 ? */
?6
?7 package ?corejava;
?8
?9 import ?java.io.IOException;
10 import ?java.io.InputStream;
11 import ?java.io.OutputStream;
12 import ?java.io.PrintWriter;
13 import ?java.net.ServerSocket;
14 import ?java.net.Socket;
15 import ?java.util.Scanner;
16
17 /**?*/ /**
18 ?*
19 ?*? @author ?livahu
20 ? */
21 public ? class ?ThreadedEchoServer? {
22 ????
23 ???? /**?*/ /** ?Creates?a?new?instance?of?ThreadedEchoServer? */
24 ???? public ?ThreadedEchoServer()? {
25 ????}
26 ????
27 ???? public ? static ? void ?main(String[]?args)? {
28 ???????? try ? {
29 ???????????? int ?i? = ? 1 ;
30 ????????????ServerSocket?s? = ? new ?ServerSocket( 8189 );
31 ????????????
32 ???????????? while ?( true )? {
33 ????????????????Socket?incoming? = ?s.accept();
34 ????????????????System.out.println( " Spawning? " ? + ?i);
35 ????????????????Runnable?r? = ? new ?ThreadedEchoHandler(incoming,?i);
36 ????????????????Thread?t? = ? new ?Thread(r);
37 ????????????????t.start();
38 ????????????????i ++ ;
39 ????????????}
40 ????????} ? catch ?(IOException?ex)? {
41 ????????????ex.printStackTrace();
42 ????????}
43 ????}
44 }
45
46 class ?ThreadedEchoHandler? implements ?Runnable? {
47 ???? private ?Socket?incoming;
48 ???? private ? int ?counter;
49 ????
50 ???? public ?ThreadedEchoHandler(Socket?i,? int ?c)? {
51 ????????incoming? = ?i;
52 ????????counter? = ?c;
53 ????}
54 ????
55 ???? public ? void ?run()? {
56 ???????? try ? {
57 ???????????? try ? {
58 ????????????????InputStream?inStream? = ?incoming.getInputStream();
59 ????????????????OutputStream?outStream? = ?incoming.getOutputStream();
60 ????????????????
61 ????????????????Scanner?in? = ? new ?Scanner(inStream);
62 ????????????????PrintWriter?out? = ? new ?PrintWriter(outStream,? true );
63 ????????????????out.println( " Hello!?Enter?BYE?to?exit. " );
64 ????????????????
65 ???????????????? boolean ?done? = ? false ;
66 ???????????????? while ?( ! done? && ?in.hasNextLine())? {
67 ????????????????????String?line? = ?in.nextLine();
68 ????????????????????out.println( " Echo:? " ? + ?line);
69 ???????????????????? if ?(line.trim().equals( " BYE " ))
70 ????????????????????????done? = ? true ;
71 ????????????????}
72 ????????????} ? finally ? {
73 ????????????????incoming.close();
74 ????????????????
75 ????????????}
76 ????????} ? catch ?(IOException?ex)? {
77 ????????????ex.printStackTrace();
78 ????????}
79 ????}
80 ????
81 }
82

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我們來分析其中一段?
?????????????????InputStream inStream = incoming.getInputStream();

??????????????? OutputStream outStream = incoming.getOutputStream();

???????????????

??????????????? Scanner in = new Scanner(inStream);

??????????????? PrintWriter out = new PrintWriter(outStream, true);

??????????????? out.println("Hello! Enter BYE to exit.");

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incoming?是一個Socket對象，getInputStream()方法返回一個InputStream對象，用于接受用戶從文件或者鍵盤或者其它源的輸入。而getOutputStream() 方法用來返回一個OutputStream對象，用來得到一個Socket的輸出流，再用PrintWriter包裝它（或叫結合產生過濾流）為了更方便的輸出。利用out對象的println(String s)方法，我們可以把s的數據輸出到out的緩沖區里面，然后如果數據滿了緩沖區自動經過底層流輸出到顯示器或者由主機環境或用戶指定的另一個輸出目標，這里就是telnet應用程序窗口,而不是command控制臺，如果數據未寫滿緩沖區println()也會自動調用flush()方法刷新緩沖區，輸出數據。

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