Java---30---IO（一）

字符流Reader&Writer的使用方法：

1.创建：
以FileReader FileWriter为例
创建FileReader对象：

FileRead fr = new FileReader ("demo.txt");

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

2.读取/写入：
fr.read() 结束标志：返回值为-1
一次读一个，自动往下读
可以这么做：

int len = 0;

while ((len = fr.read()) != -1){
	System.out.println (len);//打印出结果是数字，可强制转换
}

char buf[] = new char[1024];
int num = 0;
while ((num = fr.read(buf)) != -1){
	System.out.println (new String (buf));
}

fw.write("shdsdhksldlksjdlksjdkl");
fw.flush ();//刷新，将内容刷进目的地

3.关闭字符流对象：

fr.close ();
fw.close ();

4.异常的处理：

以FileWriter为例，FileReader也是一样的。

FileWriter fw = null;
try {
	fw = new FileWriter("demo.txt");

	fw.write("sssssssssssssssssss");

} catch (IOException e) {
	// TODO Auto-generated catch block
	e.printStackTrace();
} finally {
	try {
		if (fw != null) {
			fw.close();
		}
	} catch (IOException e) {
		// TODO Auto-generated catch block
		e.printStackTrace();
	}
}

5.使用缓冲区提高效率：
缓冲区的出现时为了提高流的读取效率，所以在创建缓冲区之前必须要有流对象.


创建:
将需要提高效率的流对象作为参数传递给缓冲区的构造函数。

BufferedReader  bufr = new BufferedReader (new FileReader ("demo.txt"));
BufferedWriter bufw = new BufferedWriter (new FilrWriter ("demo.txt"));

String line = bufr.readLine ();

System.out.println (line);

bufw.write ("dsadsadsadsadsafrfg");
bufw.flush ();

bufr.close();
bufw.close ();

字节流 的使用方法：

1.创建：

FileOutputStream fos = new FileOutputStream ("demo.txt");

会自动创建，若有同名文件将会覆盖。

FileInputStream fis = new FileInputStream ("demo.txt");

fos.write ("dsadsadsadwerfetrythy");
fow.flush ();

int len = 0;
while ((len = fis.read ()) != -1){
	System.out.println ((char)ch);
}

byte buf[] = new byte [1024];
int len = 0;
while ((len = fis.read (buf)) != -1){
	System.out.println (new String (buf,0,len));
}

byte buf[] = new byte[fis.available()];//估计字节数
int len = 0;
while ((len  = fis.read (buf)) != -1){
	System.out.println (new String (buf,0,len));
}

4.缓冲区
将需要被提高效率的字节流对象作为参数传递给缓冲区的构造函数. 

BufferedOutputStream bufos = new BufferedOutputStream (new FileOutputStream ("demo.txt"));
BufferedInputStream bufis = new BufferedInputStream (new FileInputStream("demo.txt"));

5.关闭
有缓冲区的时候，只需要关闭缓冲区就好，没有的话调用close方法关闭流对象。 

转换流：
InputStreamReader:字节流通向字符流的桥梁   用于操作字节流的字符流对象
OutputStreamWriter:字符流通向字节流的桥梁   用于操作字符流的字节流对象

FileInputStream fis = new FileInputStream ("demo.txt");
InputStreamReader isr = new InputStreamReader (fis);
两句写成一句
InputStreamReader isr = new InputStreamReader (new FileInputStream ("demo.txt"));

FileOutputStream fis = new FIleOutputStream ("demo.txt");
OutputStreamWriter osw = new OutputStreamWriter (fis);
两句写成一句
OutputStreamWriter osw = new OutputStreamWriter (new FileOutputStream ("demo.txt"));

osw.write ("sgydgasddsagukwe");

int len = 0;
		
while ((len = isr.read()) != -1) {
	System.out.print((char)len);
}

FileInputStream fis = new FileInputStream ("demo.txt");
InputStreamReader isr = new InputStreamReader (fis);
BufferedReader bufr = new BufferedReader (isr);
三句成一句：
BufferedReader bufr = new BufferedReader (new InputStreamReader (new FileInputStream ("demo.txt")));

BufferedWriter bufw = new BufferedWriter(new OutputStreamWriter(new FileOutputStream("demo.txt")));