Day-19 IO stream

1.IO
1.1 summary
Flow is a set of sequential , Set of bytes with start and end points , Is the general term or abstraction of data transmission . That is, the transmission of data between two devices is called streaming , The essence of stream is data transmission , According to the characteristics of data transmission, streams are abstracted into various kinds , Convenient and more intuitive data operation .
I：input Input stream
O：output： Output stream
1.2 classification
According to the type of data processed , It is divided into byte stream and character stream
It is divided into input flow and output flow according to different data flow directions .（ In and out are relative to memory ）

According to different functions , It is divided into node flow and processing flow
Node flow ： Direct manipulation of data sources
Processing flow ： Process other streams
1.3 Four abstract classes

This table example ： Byte input stream ： InputStream
1.4 File stream
1.4.1 FileInputStream
summary ： Used to open the file and read the data in the file
Want to read a file , You must find it first , You must use this file stream
1. Absolute position
The system root directory shall prevail , such as D：/xxx/xxx/xxx/a.txt
2. The relative position
./ Represents the current directory
…/ Indicates the parent directory
…/…/ Go to the superior directory
1.4.2 Read Use
read： Read a byte , And return the corresponding ASCLL Code value , Return to int type , If you reach the end of the file （ After reading the ） Then return to -1
read Method overloading ： You can pass an array , One read will fill the array / After reading , And then back in one go
return int type , Is the current number of reads , If the end of the file is reached return -1
The array is equivalent to a buffer , It will improve efficiency
1.4.3 FileReader
summary ： FileReader： Read one character at a time , That's two bytes , Mainly used to read plain text , Solve the mess
read（）： Read one character at a time , Return the corresponding ASCLL code , Return at the end -1
read（char[]）: Read one character array at a time , Improve reading efficiency , Returns the number of characters read locally , Return at the end of the file -1
Usage mode

 stay public class IO_05_FileReader {
    
   public static void main(String args[]){
    
	   try(FileReader fr=new FileReader("./src/IO/b.txt");) {
    
		int temp=0;
		while((temp=fr.read())!=-1){
    
			
		}
	} catch (Exception e) {
    
		// TODO Auto-generated catch block
		e.printStackTrace();
	}
   }
} Insert the code chip here 

1.4.4 FileOutputStream
summary
FileOutputStream It's a byte output stream , Used to write data out to a specified file
If the specified file does not exist , The file will be created automatically , But it doesn't create a directory （ No folders will be created ）
Construction method

public static void main(String[] args) throws IOException {
    
		//  Overwrite write , When creating the output stream object of the file , The contents of the file will be cleared 
		// FileOutputStream fos1 = new FileOutputStream("D:/a.txt");
		
		//  When you create an object , Pass in the second parameter  true  Description is append write , The file will not be emptied 
		FileOutputStream fos1 = new FileOutputStream("D:/a.txt",true);
		fos1.write(98);
	 
	}
}

Usage mode

1.4.6 FileWriter

public static void main(String[] args) {
    
		//  Usage and byte output   Agreement   It's just a new method overload that can write out strings 
		try (FileWriter fw = new FileWriter("D:/a.txt")){
    
			//  You can write the data in the character array each time 
			char[] chars = {
    'a','c'};
			fw.write(chars);
			
			//  You can write out the string directly 
			fw.write(" how are you ?");
			
			fw.flush();
		} catch (Exception e) {
    
			e.printStackTrace();
		}
	}
}

1.4.7 Buffer flow
characteristic ：
① It exists mainly to improve efficiency , Reduce the number of physical reads
② Provide readLine()、newLine() Such a convenient way （ For buffered character stream ）
③ When reading and writing , There will be a cache part , call flush To refresh the cache , Write memory data to disk

BufferedReader

public static void main(String[] args) {
    
		try (
		//  Create character input stream 
		FileReader fr = new FileReader("./src/day_01/Test_01.java");
				//  Create character input buffer stream object 
				BufferedReader br = new BufferedReader(fr);) {
    
			// br.readLine() :  Read a row of data , Return the contents of the read row of data , by String ,  Return at the end of the file  null
			String temp = null;
			while ((temp = br.readLine()) != null) {
    
				System.out.println(temp);
			}
		} catch (Exception e) {
    
			e.printStackTrace();
		}
	}

BufferWriter

public static void main(String[] args) {
    
		try (
		//  Create character output stream 
		FileWriter fw = new FileWriter("D:/a.txt");
				//  Create character output buffer stream 
				BufferedWriter bw = new BufferedWriter(fw);) {
    
			//  Write 
			bw.write(" how are you ");
			//  Line break 
			bw.newLine();
			bw.write(" Can you manage it ");
			//  Brush cache 
			bw.flush();
		} catch (Exception e) {
    
			e.printStackTrace();
		}
	}

1.4.8 Converted flow
characteristic ：
Conversion stream refers to the conversion of bytes to character stream , There are mainly InputStreamReader and OutputStreamWriter
InputStreamReader It is mainly about converting byte input stream into character input stream
OutputStreamWriter It mainly converts byte output stream into character output stream
1.7 Print stream
Print stream is the most convenient class for output
Include byte print stream PrintStream, Character print stream PrintWriter
PrintStream yes OutputStream Subclasses of , After passing an instance of the output stream to the print stream , It is more convenient to output, which is equivalent to repacking the output stream
PrintStream Class print（） Class methods are overloaded many times print（int i）、print（boolean b）、print（char c）

public static void main(String[] args) throws Exception{
    
		//  Create output stream 
		FileOutputStream	fos = new FileOutputStream("D:/a.txt");
		//  Encapsulated as a print stream 
		PrintStream ps= new PrintStream(fos);
		ps.println(123);
		ps.println("asdasd Assad ");
		
		// System Print stream in   Print to console by default 
		System.out.println("xxxx");
		//  change System Print stream in 
		System.setOut(ps);
		
		//  All the following printing operations , No longer displayed in the console , Instead, print to the specified file 
		System.out.println("xxxxxxxxx");
		System.out.println(" how are you ");
	}

1.8 Data flow
summary
Data flow It is for the unity of data reading between different platforms ,Linux,Windows When the operating system stores data, the way is different

To address the differences between ,java Provides two lightweight methods , As long as each platform has java Environmental Science , Can ensure the consistency of data

such as During network protocol transmission , It is very applicable
Use

public class IO_14_DataOutputStream {
    
	public static void main(String[] args)  throws Exception{
    
		//  Create objects 
		DataOutputStream dos = new DataOutputStream(new FileOutputStream("D:/a.txt"));
		//  Writing data 
		dos.writeByte(1);
		dos.writeShort(12);
		dos.writeInt(51);
		dos.writeUTF(" Assad Ji'an City ");
		
		dos.flush();
		dos.close();
	}