The java.io package includes just about any category you may actually have to execute input and output (I/O) in Java. All these channels signify an input signal supply and an output location. The flow in the java.io package supports several information including primitives, Item, local figures, etc.
Stream

A flow may be described as a collection of information. You will find two types of Streams

InPutStream: The InputStream can be used to examine information from a resource.

OutPutStream: the OutputStream can be used for creating information to your location.

Java supplies powerful but elastic assistance for I/O connected to Documents and systems but this course addresses quite basic features associated with channels and that I/O. We’d notice many popular instance 1 by 1:

Byte Streams

Java byte channels are utilized to perform input and output signal of 8-bit bytes. Although you will find several groups associated with byte channels but the most commonly used categories are , FileInputStream and FileOutputStream. Following is an illustration which uses both of these groups to replicate an input document into an output document:

import java.io.*;

public class CopyFile {
   public static void main(String args[]) throws IOException
   {
      FileInputStream in = null;
      FileOutputStream out = null;

      try {
         in = new FileInputStream("input.txt");
         out = new FileOutputStream("output.txt");
         
         int c;
         while ((c = in.read()) != -1) {
            out.write(c);
         }
      }finally {
         if (in != null) {
            in.close();
         }
         if (out != null) {
            out.close();
         }
      }
   }
}
Today let us have a record input.txt using the next articles:

This can be evaluation for duplicate document.

As a next step, gather above application and run it, that may lead to making output.txt record with exactly the same articles as we've in input.txt. Thus let us set above code in CopyFile.java document and do the subsequent:

$javac CopyFile.java
$java CopyFile

Personality Streams

Java Byte avenues are employed to perform input and output signal of 8-tad bytes, where-as Java Persona channels are employed to perform input and output signal for 16-tad unicode. Although you will find several groups associated with personality channels but the most commonly used categories are , FileReader and FileWriter.. Although internally FileReader uses FileInputStream and FileWriter utilizes FileOutputStream but here important distinction is that FileReader scans two bytes in an occasion and FileWriter produces two bytes in an occasion.

We may rewrite above illustration which uses both of these groups to replicate an feedback document (having unicode figures) into an result record:
import java.io.*;
public class CopyFile {
   public static void main(String args[]) throws IOException
   {
      FileReader in = null;
      FileWriter out = null;

      try {
         in = new FileReader("input.txt");
         out = new FileWriter("output.txt");
         
         int c;
         while ((c = in.read()) != -1) {
            out.write(c);
         }
      }finally {
         if (in != null) {
            in.close();
         }
         if (out != null) {
            out.close();
         }
      }
   }
}
Today let us have a record input.txt using the next articles:

This can be evaluation for duplicate document.

As a next step, gather above application and run it, that may lead to making output.txt record with exactly the same articles as we've in input.txt. Thus let us set above code in CopyFile.java document and do the subsequent:

$javac CopyFile.java
$java CopyFile

Regular Streams

All the development dialects provide help for normal I/O where person's application may take input from a keypad after which generate output signal using the PC display. Should you be conscious if C or C development dialects, you then must be mindful of three conventional apparatus STDIN, STDOUT and STDERR. Comparable means Java supplies subsequent three regular streams

Typical Input Signal: That is utilized to feed the information to consumer's application and typically a keypad is utilized as normal feedback supply and symbolized as System.in.

Common Out-Put: This really is employed to output the information created by an individual's application and typically a monitor can be used to regular output flow and symbolized as System.out.

Common Problem: That is employed to output the error information generated by an individual's application and typically a monitor can be used to common mistake flow and symbolized as System.err.

import java.io.*;
public class ReadConsole {
   public static void main(String args[]) throws IOException
   {
      InputStreamReader cin = null;

      try {
         cin = new InputStreamReader(System.in);
         System.out.println("Enter characters, 'q' to quit.");
         char c;
         do {
            c = (char) cin.read();
            System.out.print(c);
         } while(c != 'q');
      }finally {
         if (cin != null) {
            cin.close();
         }
      }
   }
}
Pursuing is an easy application which produces InputStreamReader to examine standard enter flow until the person types a "q":Let's keep above code in ReadConsole.java file and try to compile and execute it as below. This program continues reading and outputting same character until we press 'q':
$javac ReadConsole.java
$java ReadConsole
Enter characters, 'q' to quit.
1
1
e
e
q
q

Reading and Writing Files:

As described earlier, A stream can be defined as a sequence of data. The InputStream is used to read data from a source and the OutputStream is used for writing data to a destination.

Here is a hierarchy of classes to deal with Input and Output streams.

Java I/O Streams
The two important streams are FileInputStream and FileOutputStream, which would be discussed in this tutorial:

FileInputStream:

This stream is used for reading data from the files. Objects can be created using the keyword new and there are several types of constructors available.

Following constructor takes a file name as a string to create an input stream object to read the file.:

InputStream f = new FileInputStream("C:/java/hello");

Following constructor takes a file object to create an input stream object to read the file. First we create a file object using File() method as follows:

File f = new File("C:/java/hello");
InputStream f = new FileInputStream(f);

Once you have InputStream object in hand, then there is a list of helper methods which can be used to read to stream or to do other operations on the stream.

SN Methods with Description
1 public void close() throws IOException{}This method closes the file output stream. Releases any system resources associated with the file. Throws an IOException.
2 protected void finalize()throws IOException {}This method cleans up the connection to the file. Ensures that the close method of this file output stream is called when there are no more references to this stream. Throws an IOException.
3 public int read(int r)throws IOException{}This method reads the specified byte of data from the InputStream. Returns an int. Returns the next byte of data and -1 will be returned if it’s end of file.
4 public int read(byte[] r) throws IOException{}This method reads r.length bytes from the input stream into an array. Returns the total number of bytes read. If end of file -1 will be returned.
5 public int available() throws IOException{}Gives the number of bytes that can be read from this file input stream. Returns an int.

There are other important input streams available, for more detail you can refer to the following links:

  • ByteArrayInputStream
  • DataInputStream

FileOutputStream:

FileOutputStream is used to create a file and write data into it. The stream would create a file, if it doesn’t already exist, before opening it for output.

Here are two constructors which can be used to create a FileOutputStream object.

Following constructor takes a file name as a string to create an input stream object to write the file:

OutputStream f = new FileOutputStream("C:/java/hello")

Following constructor takes a file object to create an output stream object to write the file. First, we create a file object using File() method as follows:

File f = new File("C:/java/hello");
OutputStream f = new FileOutputStream(f);

Once you have OutputStream object in hand, then there is a list of helper methods, which can be used to write to stream or to do other operations on the stream.

SN Methods with Description
1 public void close() throws IOException{}This method closes the file output stream. Releases any system resources associated with the file. Throws an IOException
2 protected void finalize()throws IOException {}This method cleans up the connection to the file. Ensures that the close method of this file output stream is called when there are no more references to this stream. Throws an IOException.
3 public void write(int w)throws IOException{}This methods writes the specified byte to the output stream.
4 public void write(byte[] w)Writes w.length bytes from the mentioned byte array to the OutputStream.

There are other important output streams available, for more detail you can refer to the following links:

  • ByteArrayOutputStream
  • DataOutputStream

Example:

Following is the example to demonstrate InputStream and OutputStream:

import java.io.*;

public class fileStreamTest{

   public static void main(String args[]){
   
   try{
      byte bWrite [] = {11,21,3,40,5};
      OutputStream os = new FileOutputStream("test.txt");
      for(int x=0; x < bWrite.length ; x++){
         os.write( bWrite[x] ); // writes the bytes
      }
      os.close();
     
      InputStream is = new FileInputStream("test.txt");
      int size = is.available();

      for(int i=0; i< size; i++){
         System.out.print((char)is.read() + "  ");
      }
      is.close();
   }catch(IOException e){
      System.out.print("Exception");
   }	
   }
}

The above code would create file test.txt and would write given numbers in binary format. Same would be output on the stdout screen.

File Navigation and I/O:

There are several other classes that we would be going through to get to know the basics of File Navigation and I/O.

Directories in Java:

A directory is a File which can contains a list of other files and directories. You use File object to create directories, to list down files available in a directory. For complete detail check a list of all the methods which you can call on File object and what are related to directories.

Creating Directories:

There are two useful File utility methods, which can be used to create directories:

  • The mkdir( ) method creates a directory, returning true on success and false on failure. Failure indicates that the path specified in the File object already exists, or that the directory cannot be created because the entire path does not exist yet.
  • The mkdirs() method creates both a directory and all the parents of the directory.

Following example creates “/tmp/user/java/bin” directory:

import java.io.File;

public class CreateDir {
   public static void main(String args[]) {
      String dirname = "/tmp/user/java/bin";
      File d = new File(dirname);
      // Create directory now.
      d.mkdirs();
  }
}

Compile and execute above code to create “/tmp/user/java/bin”.

Note: Java automatically takes care of path separators on UNIX and Windows as per conventions. If you use a forward slash (/) on a Windows version of Java, the path will still resolve correctly.

Listing Directories:

You can use list( ) method provided by File object to list down all the files and directories available in a directory as follows:

import java.io.File;

public class ReadDir {
   public static void main(String[] args) {
      
      File file = null;
      String[] paths;
            
      try{      
         // create new file object
         file = new File("/tmp");
                                 
         // array of files and directory
         paths = file.list();
            
         // for each name in the path array
         for(String path:paths)
         {
            // prints filename and directory name
            System.out.println(path);
         }
      }catch(Exception e){
         // if any error occurs
         e.printStackTrace();
      }
   }
}

This would produce following result based on the directories and files available in your /tmp directory:

test1.txt
test2.txt
ReadDir.java
ReadDir.class

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