1. Chapter9
The Java I/O System

2. ● Often a program needs to bring in information from an external source or to send out information to an external destination.
● The information can be anywhere: in a file, on disk, somewhere on the network, in memory, or in another program. Also, the information can be of any type: objects, characters, images, or sounds.

3. I/O:
Command-Line Arguments
Console I/O
Files and File I/O

4. Text-Based Applications

6. public class TestArgs {
public static void main(String[] args) {
for ( int i = 0; i < args.length; i++ ) {
System.out.println("args[" + i + "] is *" + args[i] + "*"); }
java TestArgs arg1 arg2 "another arg“
Here is an except of output:
args[0] is *arg0*
args[1] is *arg1*
args[2] is *12*

9. import java.util.Enumeration; public class TestProperties {
import java.util.Properties;
import java.util.Enumeration;
public class TestProperties {
public static void main(String[] args) {
Properties props = System.getProperties();
Enumeration prop_names = props.propertyNames();
while ( prop_names.hasMoreElements() ) {
String prop_name = (String) prop_names.nextElement();
String property = props.getProperty(prop_name);
System.out.println("property ’" + prop_name + "’ is ’" + property + "’"); }
java -DmyProp=theValue TestProperties

10. DOS:

11. EditPlus: ---------- java ----------
property ’ java.runtime.name’ is ’ Java(TM) 2 Runtime Environment, Standard Edition’
property ’sun.boot.library.path’ is ’C:\j2sdk1.4.2_06\jre\bin’
property ’java.vm.version’ is ’1.4.2_06-b03’
property ’java.vm.vendor’ is ’Sun Microsystems Inc.’
property ’java.vendor.url’ is ’
property ’path.separator’ is ’;’
property ’java.vm.name’ is ’Java HotSpot(TM) Client VM’
property ’file.encoding.pkg’ is ’sun.io’
property ’user.country’ is ’CN’ ……
property ’sun.io.unicode.encoding’ is ’UnicodeLittle’
property ’sun.cpu.isalist’ is ’pentium i486 i386’

14. Reading Java API : BufferedReader – readLine( )
import java.io.*;
public class KeyboardInput {
public static void main (String args[]) {
String s;
// Create a buffered reader to read
// each line from the keyboard.
InputStreamReader ir = new InputStreamReader(System.in);
BufferedReader in = new BufferedReader(ir);
System.out.println("Unix: Type ctrl-d or ctrl-c to exit." + "\nWindows: Type ctrl-z to exit");

15. try {
// Read each input line and echo it to the screen.
//Throws: IOException - If an I/O error occurs
s = in.readLine();
while ( s != null ) {
System.out.println("Read: " + s); }
// Close the buffered reader.
in.close();
} catch (IOException e) { // Catch any IO exceptions.
e.printStackTrace();

21. //Read by Buffered Reader
import java.io.*;
public class ReadFile {
public static void main (String [] args) {
// Create file
File file = new File(args[0]);
try {
// Create a buffered reader to read each line from a file. FileReader(file)-if the specified file is not found throws FileNotFoundException
BufferedReader in = new BufferedReader(new FileReader(file));
String s;
// Read each line from the file and echo it to the screen.
s = in.readLine();
while (s != null) {
System.out.println(s); }

22. // Close the buffered reader, which also closes the file reader.
in.close();
} catch (FileNotFoundException e1) {
// If this file does not exist
System.err.println("File not found: " + file);
} catch (IOException e2) {
// Catch any other IO exceptions.
e2.printStackTrace(); }
//java ReadFile E:\zhangjm\java\JavaLecture\教案\chapter9\code9\DaiWS.txt

23. Result:
java
戴望舒
给什么智慧给我，
小小的白蝴蝶。
翻开了空白之页，
合上了空白之页?
翻开的书页:
寂寞;
合上的书页:
寂寞.
Normal Termination
Output completed (0 sec consumed).

24. // Read file by FileReader
import java.io.*;
public class ReadFile02 {
public static void main (String [] args) {
// Create file
File file = new File(args[0]);
char [] ch = new char[8];
try {
FileReader in = new FileReader(file);
int s;
s = in.read(ch);
while (s != -1) {
System.out.println(ch); }

25. // Close the buffered reader, which also closes the file reader.
in.close();
} catch (FileNotFoundException e1) {
// If this file does not exist
System.err.println("File not found: " + file);
} catch (IOException e2) {
// Catch any other IO exceptions.
e2.printStackTrace(); }
//java ReadFile E:\zhangjm\java\JavaLecture\教案\chapter9\code9\DaiWS.txt

26. import java.io.*;
public class WriteFile {
public static void main (String args[]) {
// Create file
File file = new File(args[0]);
try {
// Create a buffered reader to read each line from standard in.
BufferedReader in
= new BufferedReader(new InputStreamReader(System.in));
// Create a print writer on this file.
PrintWriter out
= new PrintWriter(new FileWriter(file));

27. String s;
System.out.print("Enter file text. ");
System.out.println("[Type cntl-d (or ctrl-z) to stop.]");
// Read each input line and echo it to the screen.
while ((s = in.readLine()) != null) {
out.println(s); }
// Close the buffered reader and the file print writer.
in.close();
out.close();
} catch (IOException e) {
// Catch any IO exceptions.
e.printStackTrace();

28. Advanced I/O Streams

37. import java.io.*;
public class TestNodeStreams {
public static void main(String[] args) {
try {
FileReader input = new FileReader(args[0]);
FileWriter output = new FileWriter(args[1]);
char[] buffer = new char[128];
int charsRead;
// read the first buffer
// 除尾次外,每次读buffer长个字符
charsRead = input.read(buffer);

38. // write the buffer out to the output file
while ( charsRead != -1 ) {
// write the buffer out to the output file
output.write(buffer, 0, charsRead);
// read the next buffer
charsRead = input.read(buffer); }
input.close();
output.close();
} catch (IOException e) {
e.printStackTrace();

39. public class TestBufferedStreams {
import java.io.*;
public class TestBufferedStreams {
public static void main(String[] args) {
try {
FileReader input = new FileReader(args[0]);
BufferedReader bufInput = new BufferedReader(input);
FileWriter output = new FileWriter(args[1]);
BufferedWriter bufOutput = new BufferedWriter(output);
String line;
// read the first line
line = bufInput.readLine(); }

40. while ( line != null ) {
// write the line out to the output file
bufOutput.write(line, 0, line.length());
bufOutput.newLine();
// read the next line
line = bufInput.readLine(); }
bufInput.close();
bufOutput.close();
} catch (IOException e) {
e.printStackTrace();

42. An InputStreamReader is a bridge
peek:从存储器读一个字节的命令。取数。
An InputStreamReader is a bridge
from byte streams to character streams

43. public class InputStreamReader extends Reader:
An InputStreamReader is a bridge from byte streams to character streams.
public class OutputStreamWriter extends Writer:
An OutputStreamWriter is a bridge from character streams to byte streams