输入输出.ppt

输入输出流,目标,流概念 java用于输入输出流的类 数据池流的使用 处理流的使用 文件随机读取 总结,输入/输出的需求,java把这些不同类型的输入、输出抽象为流（stream），分为输入流和输出流，用统一的接口来表示， java开发环境中提供了包java.io，其中包括一系列的类来实现输入输出处理。,流：是一个数据序列。有两种流： 1. 输入流 2. 输出流,输入流 通过打开一个到数据源（文件、内存或网络端口上的数据）的输入流，程序可以从数据源上顺序读取数据。,读数据的逻辑为： open a stream while more information read information close the stream,输出流 通过打开一个到目标的输出流，程序可以向外部目标顺序写数据。,写数据的逻辑为： open a stream while more information write information close the stream,java用于输入输出流的类,按所读写的数据类型分两类： 字符流类（character streams） 字符流类用于向字符流读写16位二进制字符。 字节流类（byte streams） 字节流类用于向字节流读写8位二进制的字节。一般地，字节流类主要用于读写诸如图象或声音等的二进制数据。,java.io中的基本流类： 说明：它们是抽象类，不能直接创建对象。,inputstream 方法,the three basic read methods: int read() int read( byte buffer) int read( byte buffer, int offset, int length) the other methods: void close() int available() skip( long n),outputstream 方法,the three basic write methods: void write( int c) void write( byte buffer) void write( byte buffer, int offset, int length) the other methods: void close() void flush(),reader methods,the three basic read methods: int read() int read( char cbuf) int read( char cbuf, int offset, int length) the other methods: void close() boolean ready() skip( long n),writer 方法,the three basic write methods: void write( int c) void write( char cbuf) void write( char cbuf, int offset, int length) void write( string string) void write( string string, int offset, int length) the other methods: void close() void flush(),字节流,inputstream、outputstream fileinputstream、fileoutputstream顺序读取文件 filterinputstream、filteroutputstream过滤流（有多线程同步） datainputstream、dataoutputstream对数据类型读写，有多线程同步 bufferedinputstream、bufferedoutputstream,字符流,reader、writer inputstreamreader、outputstreamwriter filereader、filewriter bufferedreader、bufferedwriter stringreader、stringwriter,对象流,接口objectinputobjectoutput提供的一组方法，直接支持对对象的读写 objectinputstream、objectoutputstream 用来直接进行对象的读写 readobject（），writeobject（）,import java.io.*; import java.util.date; public class serializedate serializedate() date d = new date (); try fileoutputstream f =new fileoutputstream (“date.ser“); objectoutputstream s = new objectoutputstream (f); s.writeobject(“today“); s.writeobject (d); s.close (); catch (ioexception e) e.printstacktrace (); public static void main (string args) new serializedate(); ,import java.io.*; import java.util.date; public class unserializedate unserializedate () date d = null; string today; try fileinputstream f = new fileinputstream (“date.ser“); objectinputstream s = new objectinputstream (f); today = (string)s.readobject(); d = (date) s.readobject (); s.close (); catch (exception e) e.printstacktrace (); ,system.out.println( “unserialized date object from date.ser“); system.out.println(today); system.out.println(d); public static void main (string args) new unserializedate(); ,文件流,例题：将一个文件的内容拷贝到另一个文件。,file类用来访问本地文件系统中的文件和目录。 1. 创建file类 myfile = new file(“ myfile. txt“); file mydir = new file(“ mydocs“); myfile = new file( mydir, “myfile. txt“);,file类中的方法 file names: string getname() string getpath() string getabsolutepath() string getparent() boolean renameto( file newname),file tests: boolean exists() boolean canwrite() boolean canread() boolean isfile() boolean isdirectory(),general file information and utilities: long length() boolean delete() directory utilities: boolean mkdir() string list(),处理流的使用,buffered streams,对标准输出输出的操作。 system. out ：an object of printstream类 system. in：object of inputstream类 system. err：printstream,对标准输出输出的操作。 重导向标准io 在system类中允许我们重新定向标准输入、输出以及错误io流。此时要用到下述简单的静态方法调用： setin(inputstream) setout(printstream) seterr(printstream),import java.io.*; class redirecting public static void main(string args) try bufferedinputstream in = new bufferedinputstream( new fileinputstream( “redirecting.java“); / produces deprecation message: printstream out = new printstream( new bufferedoutputstream( new fileoutputstream(“test.out“); system.setin(in); system.setout(out); system.seterr(out);,bufferedreader br = new bufferedreader( new inputstreamreader(system.in); string s; while(s = br.readline() != null) system.out.println(s); out.close(); / remember this! catch(ioexception e) e.printstacktrace(); ,datainputstream and dataoutputstream 提供了允许从流读写任意对象与基本数据类型功能的方法。,public class dataiotest public static void main(string args) throws ioexception / write the data out dataoutputstream out = new dataoutputstream(new fileoutputstream(“invoice1.txt“); double prices = 19.99, 9.99, 15.99, 3.99, 4.99 ; int units = 12, 8, 13, 29, 50 ; string descs = “java t-shirt“, “java mug“, “duke juggling dolls“, “java pin“, “java key chain“ ;,for (int i = 0; i prices.length; i +) out.writedouble(pricesi); out.writechar(t); out.writeint(unitsi); out.writechar(t); out.writechars(descsi); out.writechar(n); out.close(); / read it in again datainputstream in = new datainputstream(new fileinputstream(“invoice1.txt“); double price; int unit; string desc; double total = 0.0;,try while (true) price = in.readdouble(); in.readchar(); / throws out the tab unit = in.readint(); in.readchar(); / throws out the tab desc = in.readline(); system.out.println(“youve ordered “ + unit + “ units of “ + desc + “ at $“ + price); total = total