Java I/O 

👉Definition: Java I/O is the ability to read and write data from/to File System/network/database/memory/Console etc.

For reading writing we need to make OS call and making OS call we need libraries Known as java.io.* libraries.

There are two I/O libraries java.io & java.nio (nio- non-synchronous I/O).

👉Read/Write character

📑Read

FileReader fr = new FileReader("C:/test.txt");

fr.read();
//if file path already exists and we want to append.
FileWriter fw = new FileWriter("C:/test.txt", true);

🖋 Read from in.txt file and write out.txt to file

 FileReader fr;
 FileWriter fw;
 try{
 fr = new FileReader("C:/in.txt");
 fw = new FileWriter("C:/out.txt");
 int x
    while((x = fr.read()) != -1){
    fw.write(x);
    }
 }catch(IOException e){
            e.printStackTrace();
 }
 finally{
 try{
 if(fr != null )
    fr.close();
 }catch(IOException e){
            e.printStackTrace();
 }
try{
if(fw != null)
    fw.close();
}catch(IOException e){
            e.printStackTrace();
 }
 }

🤔 The above code will work fine but it is bad code because it is reading each character at a time so to avoid these we will use buffering.

BufferReadFile

 File fi = new file("path");

 BufferedReader br = null;
 try{
    br = new BufferedReader(new FileReader(fi));
    String line;
    while((line = br.readLine()) != null)
    {
            System.out.println(line);
    }
 }catch(IoException e){
 e.printStackTrace();
 }finally{ try{
 if(br != null)
    br.close();
 }catch(IOException e){
        e.printStackTrace();
 }
 }

BufferedWriter

 File fi = new file("path");
 File fo = new file("path");
 BufferedReader br = null;
 BufferedWriter bw = null;
 try{
    br = new BufferedReader(new FileReader(fi));
    bw = new BufferedWriter(new FileWriter(fo, true));
    String line;
    while((line = br.readLine()) != null)
    {
            System.out.println(line);
            bw.append(line);
            bw.newLine();
    }
 }catch(IoException e){
 e.printStackTrace();
 }finally{ try{
 if(bw != null)
    bw.close();
 }catch(IOException e){
        e.printStackTrace();
 }
 try{
 if(br != null)
    br.close();
 }catch(IOException e){
        e.printStackTrace();
 }
 }