java-io初步：Reader、Writer、Buf…

java四个基本的io基类：

字节流：InputStream、OutputStream

字符流：Reader、Writer.——作为硬盘的文件使用的两个子类：FileWriter、FileReader.

1、java早期只有字节流，后边由于处理不同字符的编码需求，出现了字符流.

2、java io体系中子类的命名通常都是以父类的名称作为后缀.

import java.io.*;

class IODemo

{

public static void main(String[] args) // throws
Exception

{

//fileWrite();

//fileRead();

//bufferdWrite();

//bufferdRead();

//通过缓冲区拷贝一个.java文件

copyJavaFile();

}

public static void fileWrite()

{

FileWriter fw =
null; //fw.close()调用需要引用fw.

try

{

fw = new
FileWriter("iodemo.txt", false); //第二个参数决定是否向覆盖原文件.

fw.write("sddddddd");

fw.write("\r\naaa"); //windows\r\n为一个回车符.

}

catch (Exception e)

{

System.out.println(e.toString());

}

finally

{

try

{

fw.close();

}

catch
(Exception e)

{

System.out.println(e.toString());

}

}

}

public static void fileRead()

{

//读取文件通用格式:

//建立字符流读取对象，于指定文件关联

FileReader fr = null;

try

{

fr = new
FileReader("iodemo.txt");

char[] arr =
new char[1024]; //将读出的数据存入到数组中.(缓存)

int num =
0;

while ((num =
fr.read(arr)) != -1) //没有读到数据后，返回-1，循环结束;read方法可以自动向后读取剩下的数据,

{

System.out.println(new
String(arr, 0, num));

}

}

catch (Exception e)

{

System.out.println(e.toString());

}

finally

{

try

{

fr.close();

}

catch
(Exception e)

{

System.out.println(e.toString());

}

}

}

public static void bufferdWrite()

{

//创建流对象

FileWriter fw = null;

//创建缓冲区跟流对象关联。

BufferedWriter bfdw =
null;

try

{

fw = new
FileWriter("iodemo.txt");

bfdw = new
BufferedWriter(fw);

int i =
0;

while (i
< 5)

{

bfdw.write("aaa"
+ i);

bfdw.newLine();

bfdw.flush();

i++;

}

bfdw.write("xxx");
//不调用flush或close，这一行数据不能写入.

bfdw.newLine();

}

catch (Exception e)

{

System.out.println(e.toString());

}

finally

{

try

{

bfdw.close();
//缓冲区的关闭是调用传入流的关闭方法.

}

catch
(Exception e)

{

System.out.println(e.toString());

}

}

}

public static void bufferdRead()

{

//创建流对象

FileReader fr = null;

//创建缓冲区跟流对象关联。

BufferedReader bfdr =
null;

try

{

fr = new
FileReader("iodemo.txt");

bfdr = new
BufferedReader(fr);

String
s;

while ( (s =
bfdr.readLine()) != null)

{

System.out.println(s);

}

}

catch (Exception e)

{

System.out.println(e.toString());

}

finally

{

try

{

bfdr.close();
//缓冲区的关闭是调用传入流的关闭方法.

}

catch
(Exception e)

{

System.out.println(e.toString());

}

}

}

public static void copyJavaFile()

{

//创建流对象

FileReader fr = null;

FileWriter fw = null;

//创建缓冲区跟流对象关联。

BufferedReader bfdr =
null;

BufferedWriter bfdw =
null;

try

{

fr = new
FileReader("iodemo.java");

fw = new
FileWriter("iodemo复件.txt");

bfdr = new
BufferedReader(fr);

bfdw = new
BufferedWriter(fw);

String
line;

while ( (line
= bfdr.readLine()) != null)
//readLine没有读取回车符，只读取了回车符前的数据，因此写入文本时需要执行newLine方法.

{

bfdw.write(line);

bfdw.newLine();

bfdw.flush();

//System.out.println(line);

}

}

catch (IOException e)

{

System.out.println(e.toString());

}

finally

{

//对两个缓冲区分别进行关闭

if (bfdw !=
null)

{

try

{

bfdw.close();

}

catch
(Exception e)

{

System.out.println(e.toString());

}

}

if (bfdr !=
null)

{

try

{

bfdr.close();

}

catch
(Exception e)

{

System.out.println(e.toString());

}

}

}

}

}