Detailed explanation of IO stream concepts, FileWriter class and FileReader class

Table of contents

IO flow overview and classification

​Edit FileWriter to write data

FileWriter method of writing data

Frequently Asked Questions about Writing Data with FileWriter

 FileReader reads data

IOStream Overview and Classification

• IO streams are used to handle data transfer between devices

        –文品复法,上传文目和下载文目

• IO flow classification

        –Outflow——FileWriter

        –Input flow——FileReader

Detailed explanation of the diagram:

Input stream: Read the text content, display it on the monitor, use it, and use FileWriter to operate it.

Output stream: If you want to update the text content, add some content to it and use FileReader to operate.

FileWriter writes data

• Construction method

        –FileWriter(String fileName)

• member method

        –void write(String str)

        –void flush()——清缓冲

        –void close()——关闭文品

package com.demo01;

import java.io.FileWriter;
import java.io.IOException;

/**
 * 
 * @author 无限嚣张(菜菜)
 * 需求：从文件中写数据
 * 
 * FileWriter(String fileName)：传递一个文件名称
 * 
 * 输出流写数据步骤：
 * 		A：创建输出流对象
 * 		B：调用输出流写数据的方法
 * 		C：释放资源
 *
 */
public class FileWriterDemo {
	public static void main(String[] args) throws IOException {
		//创建一个文件对象
		FileWriter fw = new FileWriter("c:\\zahng.txt");
		/*
		 * 创建输出流对象做了哪些事情：
		 * 		A:调用系统资源创建一个文件
		 * 		B:创建输出流对象
		 * 		C:把输出流对象指向文件
		 */
		
		//调用输出流对象的写数据的方法
		//写一个字符串数组
		fw.write("IO流你好,HELLO");
		//数据没有直接写到文件，其实写到了内存缓冲区
		fw.flush();
		
		//释放资源
		//ͨ通知系统释放和该文件相关的资源
		//关闭文件输出流
		fw.close();
		
	}
}

If it is closed: can I write again? After executing fw.close(), no more content can be written.

FileWriterHow to write data

• void write(String str): Write a string data
• void write(String str,int index,int len): Write part of the data in a string
• void write(int ch): write a character data
• void write(char[] chs): Write a character array
• void write(char[] chs,int index,int len): Write part of the data of a character array

package com.demo01;

import java.io.FileWriter;
import java.io.IOException;

/*
 * void write(String str):写一个字符串数据
 * void write(String str,int index,int len):写一个字符串中的一部分数据
 * void write(int ch):写一个字符数据
 * void write(char[] chs):写一个字符数组
 * void write(char[] chs,int index,int len):写一个字符数组的一部分数据
 */
public class FileWriterDemo3 {
	public static void main(String[] args) throws IOException {
		//创建一个文件对象
		FileWriter fw = new FileWriter("c://zy.txt");
		
		//void write(String str):写一个字符串数组
		fw.write("abcde");
		fw.write("\r\n");
		
		//void write(String str,int index,int len):写一个字符串中的一部分数据
		fw.write("abcde",0,5);
		fw.write("\r\n");
		fw.write("abcde",1,3);
		fw.write("\r\n");
		
		//void write(int ch):void write(int ch):写一个字符数据
		fw.write('a');
		fw.write(97);
		fw.write("\r\n");
		
		//void write(char[] chs):写一个字符数组
		char[] chs = {'a','b','c','d','e'};
		fw.write(chs);
		fw.write("\r\n");
		
		//void write(char[] chs,int index,int len):写一个字符数组的一部分数据
		fw.write(chs,0,5);
		fw.write("\r\n");
		fw.write(chs,2,3);
		fw.write("\r\n");
		//关闭文件
		fw.close();
	}
}

think?????

FileWriterFrequently Asked Questions about Writing Data

 1. How to achieve line wrapping of data?

        windows:\r\n

        linux:\n

        mac:\r

 2. How to implement additional writing of data?

        FileWriter fw = new FileWriter("c.text");

package com.demo01;

import java.io.FileWriter;
import java.io.IOException;


public class FileWriterDemo4 {
	public static void main(String[] args) throws IOException {
		//FileWriter fw = new FileWriter("c://c.txt"); 
		FileWriter fw = new FileWriter("c://c.txt",true); //表示追加输入，默认是false
		
		for(int x=0; x<10; x++) {
			fw.write("hello world"+x);
			fw.write("\r\n");
		}
		
		//关闭文件
		fw.close();
	}
}

 FileReaderNumber of instructions

• Construction method

        –FileReader(String fileName)

• member method

        –int read()

        –int read(char[] cbuf)

Reading without parameters

package com.demo02;

import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;

/*
 * 需求：从文件中读数据并显示到控制台
 * 		读数据——输入流——FileReader
 * 
 * FileReader:
 * 		FileReader(String fileName):传递文件名称
 * 
 * 输入流读文件的步骤
 * 		A:创建输入流对象
 * 		B:调用输入流对象读数据的方法
 * 		C:释放资源
 * 
 * java.io.FileNotFoundException: fr.txt (系统不指定文件)
 */
public class FileReaderDemo {
	public static void main(String[] args) throws IOException {
		//创建输入流对象
		FileReader fr = new FileReader("c://zy.txt");

		int ch;
		while ((ch = fr.read()) != -1) {
			System.out.print((char) ch);
		}

		//释放
		fr.close();
	}
}

 Data reading with parameters

package com.demo02;

import java.io.FileReader;
import java.io.IOException;

/*
 * 输入流读数据的步骤
 * 		A:创建输入流对象
 * 		B:调用输入流对象的读数据的方法
 * 		C:释放资源
 */
public class FileReaderDemo2 {
	public static void main(String[] args) throws IOException {

		// 创建文件数据对象
		FileReader fr = new FileReader("c://zy.txt");
		
	
		char[] chs = new char[1024]; //创建数组对象
		int len;
		//1:fr.read(chs)
		//2:len=fr.read(chs)
		//3:len != -1
		while((len=fr.read(chs))!=-1) {
			//System.out.println(new String(chs,0,len));
			System.out.print(new String(chs,0,len));
		}
		
		//释放数据
		fr.close();
	}
}