Java Input and Output Streams working

Java provides a robust and flexible way to work with input and output streams, allowing you to read and write data to various sources such as files, network connections, and standard input/output. In this article, we will explore the fundamental concepts and techniques for handling input and output streams in Java.


Input Streams


Input streams in Java are used for reading data from different sources. Here are a few common sources and destinations where streams are used in Java:


File Input and Output:


  • Reading from and writing to files on the local file system.
  • Example sources: Text files, binary files, configuration files.
  • Example classes: FileInputStream, FileOutputStream, FileReader, FileWriter.

Network Sockets:


  • Communicating with remote servers and clients over networks.
  • Example sources: Data from remote servers, network requests, HTTP responses.
  • Example classes: Socket, ServerSocket, InputStream, OutputStream.


Some commonly used input stream classes include FileInputStream for reading from files and BufferedReader for reading text data efficiently. Here's how to work with input streams:

Reading from a File

To read data from a file, you can use the FileInputStream class:


try (FileInputStream fis = new FileInputStream("input.txt")) {
   int data;
   while ((data = != -1) {
       // The condition (data = != -1 checks if there is more data to read.
       // It continues reading until the end of the stream is reached.
       // Process the data here (You can add code to handle or display the data)
       System.out.print((char)data); // Example: Displaying the data as characters
} catch (IOException e) {


The provided code reads the contents of a file named "input.txt" character by character and prints those characters to the console. Here's an example of what the output might look like if the "input.txt" file contains the text "Hello, World!":

Output :

Hello, World!

Each character from the file is read one at a time, and System.out.print((char)data); is used to print the characters to the console. The loop continues until all characters in the file have been read.


Reading Text Data

In this section, we'll demonstrate how to read text data from a file in Java using input streams. For our example, we have a sample text file named "example.txt" with the following content:


Sample text file (example.txt):

This is line 1 of the sample text file.
Here is line 2 with some more text.
And this is the third line for demonstration.


We'll use this file as an input source for our code.

To read text data from a file, you can use the FileInputStream and BufferedReader classes. Here's a Java code snippet to accomplish this task:


public class ReadTextFileExample {
   public static void main(String[] args) {
       try (BufferedReader reader = new BufferedReader(new FileReader("example.txt"))) {
           String line;
           while ((line = reader.readLine()) != null) {
       } catch (IOException e) {



This is line 1 of the sample text file.
Here is line 2 with some more text.
And this is the third line for demonstration.


In this code, we:

Open the file "example.txt" for reading using FileReader and wrap it in a BufferedReader for efficient line-by-line reading.

Use a while loop to read each line from the file using readLine() until we reach the end of the file (when readLine() returns null).

Print each line to the console using System.out.println().

This code reads the text data from the file and displays it on the console, producing the output shown above. You can replace "example.txt" with the path to your own text file to read its content.


Output Streams

Output streams in Java are used for writing data to different destinations. The commonly used output stream classes include FileOutputStream for writing to files and PrintWriter for writing text data. Here's how to work with output streams:

Writing to a File

To write data to a file, you can use the FileOutputStream class:


try (FileOutputStream fos = new FileOutputStream("output.txt")) {
   String data = "Hello, World!";
   byte[] bytes = data.getBytes();
} catch (IOException e) {


Writing Text Data

For writing text data efficiently, you can use PrintWriter:

try (PrintWriter writer = new PrintWriter(new FileWriter("textfile.txt"))) {
   writer.println("Line 1");
   writer.println("Line 2");
   // ...
} catch (IOException e) {


Standard Input and Output Streams


Java provides standard input ( and standard output (System.out) streams, which allow you to interact with the console. Here's how to use them:


Reading from Standard Input

To read data from the console, you can use with a Scanner:


import java.util.Scanner;

Scanner scanner = new Scanner(;
System.out.print("Enter your name: ");
String name = scanner.nextLine();
System.out.println("Hello, " + name);


Writing to Standard Output

To write data to the console, you can use System.out directly or through System.out.println():


System.out.print("This is a message.");
System.out.println("This is a new line.");


Closing Streams

Properly closing streams is essential to release system resources and prevent resource leaks. Java provides a convenient way to ensure stream closure using try-with-resources blocks. In the examples above, you can see how we use try-with-resources to automatically close the streams (FileReader, BufferedReader) once they are no longer needed.

By using try-with-resources, you don't need to explicitly call the close() method on the streams. When the try block is exited (whether normally or due to an exception), Java automatically closes the resources for you.

This approach enhances the readability of your code and ensures that you won't forget to close streams, leading to more robust and resource-efficient applications.

Exception Handling

When working with streams, it's essential to handle exceptions properly. Most stream operations can throw IOException, so use try-catch blocks or propagate exceptions to handle errors gracefully.



Working with input and output streams is a fundamental skill in Java programming. Whether you're reading from files, writing to the console, or dealing with network connections, Java's input and output stream classes provide a flexible and reliable way to handle data. By following the techniques and best practices outlined in this article, you can effectively read and write data in Java and build robust applications that interact with various data sources.

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