Java I/O

Java uses the concept of stream to make I/O operation fast.

Stream

A stream is a sequence of data.In Java a stream is composed of bytes

1) System.out: standard output stream

2) System.in: standard input stream

3) System.err: standard error stream

Let’s see the code to get input from console.

int i=System.in.read();//returns ASCII code of 1st character  
System.out.println((char)i);//will print the character  

OutputStream

Java application uses an output stream to write data to a destination, it may be a file,an array,peripheral device or socket.
write data–>a destination

InputStream

Java application uses an input stream to read data from a source, it may be a file,an array,peripheral device or socket.
a source –>read data

FileInputStream and FileOutputStream (File Handling)
are used to read and write data in file.

import java.io.*;  
class Test{  
  public static void main(String args[]){  
   try{  
     FileOutputstream fout=new FileOutputStream("abc.txt");
     //讀取文件
     String s="Sachin Tendulkar is my favourite player";  
     byte b[]=s.getBytes();//converting string into byte array  
     fout.write(b);  
     fout.close();  
     System.out.println("success...");  
    }catch(Exception e){system.out.println(e);}  
  }  
}  

//把String轉化爲Byte->寫入文檔

Java FileInputStream class

Java FileInputStream class obtains input bytes from a file.It is used for reading streams of raw bytes such as image data. For reading streams of characters, consider using FileReader.

It should be used to read byte-oriented data for example to read image, audio, video etc.

import java.io.*;  
class SimpleRead{  
 public static void main(String args[]){  
  try{  
    FileInputStream fin=new FileInputStream("abc.txt");  
    int i=0;  
    while((i=fin.read())!=-1){  
     System.out.println((char)i);  
    }  
    fin.close();  
  }catch(Exception e){system.out.println(e);}  
 }  
}

Example of Reading the data of current java file and writing it into another file

We can read the data of any file using the FileInputStream class whether it is java file, image file, video file etc. In this example, we are reading the data of C.java file and writing it into another file M.java.

import java.io.*;  
class C{  
public static void main(String args[])throws Exception{  
    FileInputStream fin=new FileInputStream("C.java");  
    FileOutputStream fout=new FileOutputStream("M.java");  
    int i=0;  
    while((i=fin.read())!=-1){  
    fout.write((byte)i);  
    }  
    fin.close();  
    }  
}  

ByteArrayOutputStream
Java ByteArrayOutputStream class is used to write data into multiple files. In this stream, the data is written into a byte array that can be written to multiple stream.

import java.io.*;  
class S{  
 public static void main(String args[])throws Exception{  
  FileOutputStream fout1=new FileOutputStream("f1.txt");  
  FileOutputStream fout2=new FileOutputStream("f2.txt");  

  ByteArrayOutputStream bout=new ByteArrayOutputStream();  
  bout.write(139);  
  bout.writeTo(fout1);  
  bout.writeTo(fout2);  

  bout.flush();  
  bout.close();//has no effect  
  System.out.println("success...");  
 }  
}