1.流的概念
定义：数据流是指所有的数据通信通道
分类：
2.标准输入输出流(键盘，屏幕)
1)重要概念
标准输入输出都是System类中定义的类成员变量:
System.in:InputStream类型的,代表标准输入流，这个流是已经打开了的，默认状态对应于键盘输入。
System.out：PrintStream类型的，代表标准输出流，默认状态对应于屏幕输出
System.err：PrintStream类型的，代表标准错误信息输出流，默认状态对应于屏幕输出
也可通过重导向方法进行重新指定:
setIn(InputStream)： 指定新的标准输入流
setOut(PrintStream)：指定新的标准输出流
setErr(PrintStream)：指定新的标准错误输出流
2)键盘输入，屏幕输出
1 import java.io.*; 2 public class Echo 3 { 4 public static void main(String[] args) throws IOException 5 { 6 BufferedReader in = new BufferedReader(new InputStreamReader(System.in)); 7 String s; 8 while((s = in.readLine()).length() != 0) 9 System.out.println(s); 10 } 11 } 说明：
①以System.in作为参数，进一步创建了一个InputStreamReader流对象，它相当于字节流和字符流之间的一座桥梁，读取字节并将其转换为字符。
②BufferedReader用于对InputStreamReader处理后的信息进行缓冲,提高效率，它们都属于处理流。
3.文件操作
3.1文本文件（FileWriter,BufferedWriter,FileReader,BufferedReader）
写：
1 import java.io.*; 2 class Ex6_4 3 {4 public static void main ( String[] args ) throws IOException 5 {6 String fileName = "C://newHello.txt" ;7 - BufferedWriter out = new BufferedWriter(new FileWriter(fileName));
8 out.write( "Hello!" );9 out.newLine() ; 10 out.write( "This is another text file using BufferedWriter," ); 11 out.newLine(); ;12 out.write( "So I can use a common way to start a newline" ); 13 out.close();14 }15 } 读 ：
1 import java.io.*;2 class Ex6_5 3 {4 public static void main ( String[] args ) 5 {6 String fileName = "C:/Hello.txt" , line;7 try 8 {9 BufferedReader in = new BufferedReader(new FileReader(fileName));10 line = in.readLine(); //读取一行内容11 while ( line != null ) 12 { 13 System.out.println( line );14 line = in.readLine();15 }16 in.close(); 17 }18 catch ( IOException iox ) 19 { 20 System.out.println("Problem reading " + fileName ); 21 }22 }23 }
3.2二进制文件（非字符）
写：
基类：OutputStream
继承类:①FileOutputStream
②DataOutputStream:具有写各种基本数据类型的方法(属于过滤流)
③BufferedOutputStream:对于大量数据的写入，可以提高效率(属于过滤流)
1 import java.io.*; 2 class Ex6_83 {4 public static void main (String[] args) throws IOException 5 {6 String fileName = "mixedTypes.dat" ;7 DataOutputStream dataOut = new DataOutputStream(new BufferedOutputStream(8 new FileOutputStream(fileName)));9 dataOut.writeInt(0);10 System.out.println(dataOut.size() + " bytes have been written.");11 dataOut.writeDouble(31.2);12 System.out.println(dataOut.size() + " bytes have been written.");13 dataOut.writeBytes("JAVA");14 System.out.println(dataOut.size() + " bytes have been written.");15 dataOut.close();16 }17 }
读：
基类：InputStream
继承类:①FileInputStream
②DataInputStream:具有写各种基本数据类型的方法(属于过滤流)
③BufferedInputStream:对于大量数据的写入，可以提高效率(属于过滤流)
1 import java.io.*;2 public class Ex6_12 3 {4 public static void main(String[] args) throws IOException 5 {6 FileInputStream s=new 7 FileInputStream("c://Hello.txt");8 int c;9 while ((c = s.read()) != -1) 10 System.out.write(c); 11 s.close();12 }13 }
读写综合题：
读写下面的发票数据：
price unit description
19.99 12 Java T-shirt
9.99 8 Java Mug
STEP1:使DataOutputStream 和另一个输出流建立连接
1 DataOutputStream out = new DataOutputStream(new FileOutputStream("invoice1.txt")); STEP2:用DataOutputStream专门的write方法将上述发票数据写到invoice1.txt
1 for (int i = 0; i < prices.length; i ++) 2 {3 out.writeDouble(prices[i]); //单价4 out.writeChar('/t');5 out.writeInt(units[i]); //数量6 out.writeChar('/t');7 out.writeChars(descs[i]); //描述8 out.writeChar('/n');9 }10 out.close(); STEP3:基于刚生成的文件建立一个DataInputStream
1 DataInputStream in = new DataInputStream(new FileInputStream("invoice1.txt")); STEP4:通过DataInputStream专门的read方法把数据读取回来
1 try 2 {3 while (true) 4 {5 price = in.readDouble();6 in.readChar(); //throws out the tab7 unit = in.readInt();8 in.readChar(); //throws out the tab9 char chr;10 desc = new StringBuffer(20); 11 while ((chr = in.readChar() != '/n') 12 { desc.append(chr); }13 System.out.println("You've ordered " + unit + " units of " 14 + desc + " at $" + price);15 total = total + unit * price;16 } 17 } 18 catch (EOFException e) { }19 System.out.println("For a TOTAL of: $" + total);20 in.close();
