java中字符流总结

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字符流出现的原因和形式

由于字节流操作中文时,会将一个中文根据不同的编码表转化为不同的字节来读
    而字符流遇到中文时会根据一个一个中文来读(以中文为单位)
    
      编码表:
      Unicode：国际标准码，融合了多种文字。
        所有文字都用两个字节来表示,Java语言使用的就是unicode
        
    UTF-8：最多用三个字节来表示一个字符。
    UTF-8不同，它定义了一种“区间规则”，这种规则可以和ASCII编码保持最大程度的兼容：
    它将Unicode编码为00000000-0000007F的字符，用单个字节来表示
    它将Unicode编码为00000080-000007FF的字符用两个字节表示 
    它将Unicode编码为00000800-0000FFFF的字符用3字节表示 
      
      字符流=字节流+编码表。

三大类字符流

    InputStreamReaderAndWriter

    InputStreamReader的方法

       int read():一次读取一个字符

      int read(char[] chs):一次读取一个字符数组

InputStreamReader re = new InputStreamReader(new FileInputStream(
				"a.txt"));

		// 一次读取一个字符
		// int ch = 0;
		// while ((ch = re.read()) != -1) {
		// System.out.print((char) ch);
		// }

		// 一次读取一个字符数组
		char[] chs = new char[1024];
		int len = 0;
		while ((len = re.read(chs)) != -1) {
			System.out.print(new String(chs, 0, len));
		}

		// 释放资源
		isr.close();

    OutputStreamWriter的方法

          public void write(int c):写一个字符

          public void write(char[] cbuf,int off,int len):写一个字符数组的一部分

// 封装数据源
		InputStreamReader isr = new InputStreamReader(new FileInputStream(
				"a.txt"));
		// 封装目的地
		OutputStreamWriter osw = new OutputStreamWriter(new FileOutputStream(
				"b.txt"));

		// 读写数据
		// 方式1
		// int ch = 0;
		// while ((ch = isr.read()) != -1) {
		// osw.write(ch);
		// }

		// 方式2
		char[] chs = new char[1024];
		int len = 0;
		while ((len = isr.read(chs)) != -1) {
			osw.write(chs, 0, len);
			// osw.flush();
		}

		// 释放资源
		osw.close();
		isr.close();

  FileWriterAndReader:

      其实文件字符流的读写方法与InputStreamReaderAndWriter方法一样只是在构造方法中之间可以加文件或者文件路径。

// 封装数据源
		FileReader fr = new FileReader("a.txt");
		// 封装目的地
		FileWriter fw = new FileWriter("b.txt");

		// 一次一个字符
		// int ch = 0;
		// while ((ch = fr.read()) != -1) {
		// fw.write(ch);
		// }

		// 一次一个字符数组
		char[] chs = new char[1024];
		int len = 0;
		while ((len = fr.read(chs)) != -1) {
			fw.write(chs, 0, len);
			fw.flush();
		}

		// 释放资源
		fw.close();
		fr.close();

 BufferReaderAndWriter

    BufferReader:从字符输入流中读取文本，缓冲各个字符，从而实现字符、数组和行的高效读取。

     public String readLine() :一次读取一行

   BufferWriter:将文本写入字符输出流，缓冲各个字符，从而提供单个字符、数组和字符串的高效写入。

    public void write(String str):一次写一行

    public void newLine():加入换行符

BufferedReader reader = new BufferedReader(new InputStreamReader(new FileInputStream("g.txt")));
BufferedWriter write =  new BufferedWriter(new OutputStreamWriter(new FileOutputStream("g5.txt")));
		
	String d;
    while((d = reader.readLine())!=null){
		write.write(d);
		write.newLine();
	}
	reader.close();
	write.close();

 面试题

close和flush的区别

close():关闭流对象之前会先刷新缓冲区,关闭之后,流对象不能使用
flush():仅仅刷新缓冲区,刷新之后流对象还可以继续使用
    
一般只要close
数据大 数据达到一定值时 flush再close  不是每次都要flush
数据少 close

啥叫转换流

转换流是指将字节流转换为字符流    
InputStreamReader(InputStream in) 
FileReader(File file)  -->不是转换流

字符流和字节流的最重要的九种输入输出方式

package day21;

import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;

//将a.txt复制到f.txt
public class ByteAndChar总结Demo {

	/**
	 * @param args
	 * @throws IOException 
	 */
	public static void main(String[] args) throws IOException {
		// TODO Auto-generated method stub
		File f = new File("a.txt");
		//字节流
			mehtod(f);
			mehtod1(f);
			mehtod2(f);
			mehtod3(f);
		//字符流	
			gg(f);
			gg1(f);
			gg2(f);
			gg3(f);
			gg4(f);
	}

	private static void gg4(File f) throws IOException {
		// TODO Auto-generated method stub
		BufferedReader reader = new BufferedReader(new InputStreamReader(new FileInputStream(f)));
		BufferedWriter write =  new BufferedWriter(new OutputStreamWriter(new FileOutputStream("g5.txt")));
		
		String d;
		while((d = reader.readLine())!=null){
			write.write(d);
			write.newLine();
		}
		reader.close();
		write.close();
	}

	private static void gg3(File f) throws IOException {
		// TODO Auto-generated method stub
		InputStreamReader reader = new InputStreamReader(new FileInputStream(f));
		OutputStreamWriter write  = new OutputStreamWriter(new FileOutputStream("g.txt"));
		
		int len;
		while((len = reader.read())!=-1){
			write.write(len);
			write.flush();
		}
		
		reader.close();
		write.close();
	}

	private static void gg2(File f) throws IOException {
		// TODO Auto-generated method stub
		InputStreamReader reader = new InputStreamReader(new FileInputStream(f));
		OutputStreamWriter write  = new OutputStreamWriter(new FileOutputStream("g1.txt"));
		
		int len;
		char[] ch = new char[1024];
		while((len = reader.read(ch))!=-1){
			write.write(ch,0,len);
			write.flush();
		}
		
		reader.close();
		write.close();
	}

	private static void gg1(File f) throws IOException {
		// TODO Auto-generated method stub
		FileReader reader = new FileReader(f);
		FileWriter write = new FileWriter("g2.txt");
		int len;
		while((len = reader.read())!=-1){
			write.write(len);
			write.flush();
		}
		
		reader.close();
		write.close();
	}

	private static void gg(File f) throws IOException {
		// TODO Auto-generated method stub
		FileReader reader = new FileReader(f);
		FileWriter write = new FileWriter("g3.txt");
		int len;
		char[] ch = new char[1024];
		while((len = reader.read(ch))!=-1){
			write.write(ch,0,len);
			write.flush();
		}
		
		reader.close();
		write.close();
	}

	private static void mehtod3(File f) throws IOException {
		// TODO Auto-generated method stub
		BufferedInputStream bin = new BufferedInputStream(new FileInputStream(f));
		BufferedOutputStream bou = new BufferedOutputStream(new FileOutputStream("f3.txt"));
		
		int len;
		while((len = bin.read())!=-1){
			bou.write(len);
		}
		
		bin.close();
		bou.close();
	}

	private static void mehtod2(File f) throws IOException {
		// TODO Auto-generated method stub
		BufferedInputStream bin = new BufferedInputStream(new FileInputStream(f));
		BufferedOutputStream bou = new BufferedOutputStream(new FileOutputStream("f2.txt"));
		
		int len;
		byte[] byt = new byte[1024];
		while((len = bin.read(byt))!=-1){
			bou.write(byt,0,len);
		}
		
		bin.close();
		bou.close();
	}

	private static void mehtod1(File f)  throws IOException{
		// TODO Auto-generated method stub
		FileInputStream in = new FileInputStream(f);
		FileOutputStream out = new FileOutputStream("f1.txt");
		
		int len;
		byte[] byt = new byte[1024];
		while((len = in.read(byt))!=-1){
			out.write(byt,0,len);
		}
		
		in.close();
		out.close();
	}

	private static void mehtod(File f) throws IOException {
		// TODO Auto-generated method stub
		FileInputStream in = new FileInputStream(f);
		FileOutputStream out = new FileOutputStream("f.txt");
		
		int len;
		while((len = in.read())!=-1){
			out.write(len);
		}
		
		in.close();
		out.close();
	}

}