The flows in Java are defined as a sequence of data. There are two types of threads:

Java provides strong but flexible support for I / O associated with files and networks, but this guide covers only the basic functions associated with threads and I / O. Let's consider the most common examples in the following order.

Byte streams in Java are used to implement the input and output of 8-bit bytes. Despite the many classes associated with byte streams, the most common use is the following classes: FileInputStream and FileOutputStream. Below is an example illustrating the use of the data of two classes for copying from one file to another.

import java.io.*;
public class FileCopy {

   public static void main(String args[]) throws IOException {  
      FileInputStream fileIn = null;
      FileOutputStream fileOut = null;

      try {
         fileIn = new FileInputStream("file.txt");
         fileOut = new FileOutputStream("copied_file.txt");
         
         int a;
	// Copy the contents of file.txt
         while ((a = fileIn.read()) != -1) {
            fileOut.write(a); // Read the contents of the file file.txt and write to the file copied_file.txt
         }
      }finally {
         if (fileIn != null) {
            fileIn.close();
         }
         if (fileOut != null) {
            fileOut.close();
         }
      }
   }
}

Now consider the file file.txt with the following content:

The contents of file.txt

As a next step, you need to compile the java program and execute it, which will create a copied_file.txt file with the same contents as file.txt. Thus, we place the designated code in FileCopy.java and perform the following action:

$javac FileCopy.java
$java FileCopy

Example: to copy a file, you must create a file file.txt in the project folder with any or empty content.

import java.io.*;
public class FileCopy {

   public static void main(String args[]) throws IOException {
      FileReader fileIn = null;
      FileWriter fileOut = null;

      try {
         fileIn = new FileReader("file.txt");
         fileOut = new FileWriter("copied_file.txt");
         
         int a;
         while ((a = fileIn.read()) != -1) {
            fileOut.write(a);
         }
      } finally {
         if (fileIn != null) {
            fileIn.close();
         }
         if (fileOut != null) {
            fileOut.close();
         }
      }
   }
}

Now consider the file file.txt with the following content:

The contents of file.txt

As a next step, you need to compile the program and execute it, which will create a copied_file.txt file with the same contents as file.txt. Thus, we place the designated code in FileCopy.java and perform the following action:

$javac FileCopy.java
$java FileCopy

import java.io.*;
public class ReadConsole {

   public static void main(String args[]) throws IOException {
      InputStreamReader inStRe = null;

      try {
         inStRe = new InputStreamReader(System.in);
         System.out.println("Enter the characters, the 'q' character to exit.");
         char a;
         do {
            a = (char) inStRe.read();
            System.out.print(a);
         } while(a != 'q');
      }finally {
         if (inStRe != null) {
            inStRe.close();
         }
      }
   }
}

The following is a class hierarchy for managing I / O flows.

In this lesson we will consider two important threads: FileInputStream and FileOutputStream.

InputStream a = new FileInputStream("D:/myprogramm/java/test");

File a = new File("D:/myprogramm/java/test");
InputStream a = new FileInputStream(a);

There are also other available output streams, more detailed information about which is provided by the following links:

import java.io.*;
public class File {

   public static void main(String args[]) {
   
      try {
         char c[] = {'a','b','c'};
         OutputStream output = new FileOutputStream("file.txt"); // Create a text file
         for(int i = 0; i < c.length; i++) {
            output.write(c[i]); // Write each character in a text file
         }
         output.close();
     
         InputStream input = new FileInputStream("file.txt");
         int size = input.available();

         for(int j = 0; j < size; j++) {
            System.out.print((char)input.read() + " "); // Read the text file character by character
         }
         input.close();
      }catch(IOException e) {
         System.out.print("Exception");
      }	
   }
}

There are a number of other classes that we have to consider in order to familiarize ourselves with the basics of navigation in the file system and I / O.

There are two utility File methods that can be used to create directories:

The following Example shows the creation of the folder "/java/wikitechy/newdir":

import java.io.File;
public class CreateDirectory {

   public static void main(String args[]) {
      String nameDir = "/java/wikitechy/newdir";
      File a = new File(nameDir);
      
    // Create a folder on the disk and all the upstream directories
      a.mkdirs();
   }
}

Compile and run the following code to create the directory "/java/wikitechy/newdir". Note:Java automatically generates path separators on UNIX and Windows with regard to conventions. If you use a slash (/) while working with Java on a Windows system, the path is correctly resolved.

import java.io.File;
public class ReadDirectory {

   public static void main(String[] args) {
      File pathDir = null;
      String[] pathsFilesAndDir;
  
      try {      
        // Create a new file
         pathDir = new File("/NetBeans 8.2/Projects/ReadDirectory/ReadDirectory/"); // There must be a specified directory on the disk, otherwise the program will generate an error

         // Array of files and folders
         pathsFilesAndDir = pathDir.list();

         for(String path:pathsFilesAndDir) {
          // List files and directories
            System.out.println(path);
         }
      }catch(Exception e) {
        // If an error occurred
         e.printStackTrace();
      }
   } 
}

The result, based on the directories and files available in your/NetBeans directory 8.2/Projects/ReadDirectory/ReadDirectory /:

build
build.xml
manifest.mf
nbproject
src
ReadDirectory