Java IO - Input/Output in Java with Examples
Last Updated :
12 Jul, 2025
Java provides various Streams with its I/O package that helps the user to perform all the input-output operations. These streams support all the types of objects, data-types, characters, files, etc., to fully execute the I/O operations.
The image below demonstrates the flow of data from a source to a destination.

Standard or Default Streams in Java
Before exploring various input and output streams, let's look at 3 standard or default streams that Java has to provide, which are also most commonly used:
- System.in: This is the standard input stream (System.in) that is used to read characters from the keyboard or any other standard input device.
- System.out: This is the standard output stream (System.out) that is used to produce the result of a program on an output device like the computer screen.
Here is a list of the various print functions that we use to output statements:
Java Print Functions Used with System.out
Now, we are going to discuss the main print function used with System.out which are listed below:
1. print(): This method in Java is used to display a text on the console. This text is passed as the parameter to this method in the form of String. This method prints the text on the console and the cursor remains at the end of the text at the console. The next printing takes place from just here.
Syntax:
System.out.print(parameter);
Example:
Java
// Java program to illustrate print()
import java.io.*;
class Geeks {
public static void main(String[] args)
{
// using print()
// all are printed in the
// same line
System.out.print("GfG! ");
System.out.print("GfG! ");
System.out.print("GfG! ");
}
}
2. println(): This method in Java is also used to display a text on the console. It prints the text on the console and the cursor moves to the start of the next line at the console. The next printing takes place from the next line.
Syntax:
System.out.println(parameter);
Example:
Java
// Java program to illustrate println()
import java.io.*;
class Geeks {
public static void main(String[] args)
{
// using println()
// all are printed in the
// different line
System.out.println("GfG! ");
System.out.println("GfG! ");
System.out.println("GfG! ");
}
}
3. printf(): This is the easiest of all methods as this is similar to printf in C. Note that System.out.print() and System.out.println() take a single argument, but printf() may take multiple arguments. This is used to format the output in Java.
Example:
Java
// A Java program to demonstrate
// working of printf() in Java
class Geeks {
public static void main(String[] args) {
int x = 100;
// Printing a simple integer
System.out.printf("Printing simple integer: x = %d%n", x);
// Printing a floating-point
// number with precision
System.out.printf("Formatted with precision: PI = %.2f%n", Math.PI);
float n = 5.2f;
// Formatting a float to 4 decimal places
System.out.printf("Formatted to specific width: n = %.4f%n", n);
n = 2324435.3f;
// Right-aligning and formatting a
// float to 20-character width
System.out.printf("Formatted to right margin: n = %20.4f%n", n);
}
}
OutputPrinting simple integer: x = 100
Formatted with precision: PI = 3.14
Formatted to specific width: n = 5.2000
Formatted to right margin: n = 2324435.2500
System.err Example
It is used to display the error messages. It works similarly to System.out with print(), println(), and printf() methods.
Example:
Java
// Java Program demonstrating System.err
public class Geeks {
public static void main(String[] args) {
// Using print()
System.err.print("This is an error message using print().\n");
// Using println()
System.err.println("This is another error message using println().");
//Using printf()
System.err.printf("Error code: %d, Message: %s%n", 404, "Not Found");
}
}
Output:
This is an error message using print().
This is another error message using println().
Error code: 404, Message: Not Found
Types of Streams
Depending on the type of operations, streams can be divided into two primary classes:
1. Input Stream: These streams are used to read data that must be taken as an input from a source array or file or any peripheral device. For eg., FileInputStream, BufferedInputStream, ByteArrayInputStream etc.
2. Output Stream: These streams are used to write data as outputs into an array or file or any output peripheral device. For eg., FileOutputStream, BufferedOutputStream, ByteArrayOutputStream etc.
Types of Streams Depending on the Types of File
Depending on the types of file, Streams can be divided into two primary classes which can be further divided into other classes as can be seen through the diagram below followed by the explanations.
1. ByteStream:This is used to process data byte by byte (8 bits). Though it has many classes, the FileInputStream and the FileOutputStream are the most popular ones. The FileInputStream is used to read from the source and FileOutputStream is used to write to the destination.
Here is the list of various ByteStream Classes:
Example:
Java
// Java Program illustrating the
// Byte Stream to copy
// contents of one file to another file.
import java.io.*;
public class Geeks {
public static void main(
String[] args) throws IOException
{
FileInputStream sourceStream = null;
FileOutputStream targetStream = null;
try {
sourceStream
= new FileInputStream("sorcefile.txt");
targetStream
= new FileOutputStream("targetfile.txt");
// Reading source file and writing
// content to target file byte by byte
int temp;
while ((
temp = sourceStream.read())
!= -1)
targetStream.write((byte)temp);
}
finally {
if (sourceStream != null)
sourceStream.close();
if (targetStream != null)
targetStream.close();
}
}
}
Output:
Shows contents of file test.txt
2. CharacterStream: In Java, characters are stored using Unicode conventions (Refer this for details). Character stream automatically allows us to read/write data character by character. Though it has many classes, the FileReader and the FileWriter are the most popular ones. FileReader and FileWriter are character streams used to read from the source and write to the destination respectively.
Here is the list of various CharacterStream Classes:
Stream class | Description |
---|
BufferedReader | It is used to handle buffered input stream. |
FileReader | This is an input stream that reads from file. |
InputStreamReader | This input stream is used to translate byte to character. |
OutputStreamReader | This output stream is used to translate character to byte. |
Reader | This is an abstract class that define character stream input. |
PrintWriter | This contains the most used print() and println() method |
Writer | This is an abstract class that define character stream output. |
BufferedWriter | This is used to handle buffered output stream. |
FileWriter | This is used to output stream that writes to file. |
Example:
Java
// Java Program illustrating that
// we can read a file in a human-readable
// format using FileReader
// Accessing FileReader, FileWriter,
// and IOException
import java.io.*;
public class Geeks
{
public static void main(String[] args) throws IOException
{
FileReader sourceStream = null;
try {
sourceStream = new FileReader("test.txt");
// Reading sourcefile and
// writing content to target file
// character by character.
int temp;
while (( temp = sourceStream.read())!= -1 )
System.out.println((char)temp);
}
finally {
// Closing stream as no longer in use
if (sourceStream != null)
sourceStream.close();
}
}
}
Note: Please make sure that the file test.txt is in the same directory, this file contains the text which we want to read.
Similar Reads
Java Tutorial Java is a high-level, object-oriented programming language used to build web apps, mobile applications, and enterprise software systems. It is known for its Write Once, Run Anywhere capability, which means code written in Java can run on any device that supports the Java Virtual Machine (JVM).Java s
10 min read
Basics
Introduction to JavaJava is a high-level, object-oriented programming language developed by Sun Microsystems in 1995. It is platform-independent, which means we can write code once and run it anywhere using the Java Virtual Machine (JVM). Java is mostly used for building desktop applications, web applications, Android
4 min read
Java Programming BasicsJava is one of the most popular and widely used programming language and platform. A platform is an environment that helps to develop and run programs written in any programming language. Java is fast, reliable and secure. From desktop to web applications, scientific supercomputers to gaming console
4 min read
Java MethodsJava Methods are blocks of code that perform a specific task. A method allows us to reuse code, improving both efficiency and organization. All methods in Java must belong to a class. Methods are similar to functions and expose the behavior of objects.Example: Java program to demonstrate how to crea
7 min read
Access Modifiers in JavaIn Java, access modifiers are essential tools that define how the members of a class, like variables, methods, and even the class itself, can be accessed from other parts of our program. They are an important part of building secure and modular code when designing large applications. In this article
6 min read
Arrays in JavaIn Java, an array is an important linear data structure that allows us to store multiple values of the same type. Arrays in Java are objects, like all other objects in Java, arrays implicitly inherit from the java.lang.Object class. This allows you to invoke methods defined in Object (such as toStri
9 min read
Java StringsIn Java, a String is the type of object that can store a sequence of characters enclosed by double quotes and every character is stored in 16 bits, i.e., using UTF 16-bit encoding. A string acts the same as an array of characters. Java provides a robust and flexible API for handling strings, allowin
8 min read
Regular Expressions in JavaIn Java, Regular Expressions or Regex (in short) in Java is an API for defining String patterns that can be used for searching, manipulating, and editing a string in Java. Email validation and passwords are a few areas of strings where Regex is widely used to define the constraints. Regular Expressi
7 min read
OOPs & Interfaces
Classes and Objects in JavaIn Java, classes and objects are basic concepts of Object Oriented Programming (OOPs) that are used to represent real-world concepts and entities. A class is a template to create objects having similar properties and behavior, or in other words, we can say that a class is a blueprint for objects.An
10 min read
Java ConstructorsIn Java, constructors play an important role in object creation. A constructor is a special block of code that is called when an object is created. Its main job is to initialize the object, to set up its internal state, or to assign default values to its attributes. This process happens automaticall
10 min read
Java OOP(Object Oriented Programming) ConceptsBefore Object-Oriented Programming (OOPs), most programs used a procedural approach, where the focus was on writing step-by-step functions. This made it harder to manage and reuse code in large applications.To overcome these limitations, Object-Oriented Programming was introduced. Java is built arou
10 min read
Java PackagesPackages in Java are a mechanism that encapsulates a group of classes, sub-packages and interfaces. Packages are used for: Prevent naming conflicts by allowing classes with the same name to exist in different packages, like college.staff.cse.Employee and college.staff.ee.Employee.They make it easier
8 min read
Java InterfaceAn Interface in Java programming language is defined as an abstract type used to specify the behaviour of a class. An interface in Java is a blueprint of a behaviour. A Java interface contains static constants and abstract methods. Key Properties of Interface:The interface in Java is a mechanism to
11 min read
Collections
Exception Handling
Java Exception HandlingException handling in Java is an effective mechanism for managing runtime errors to ensure the application's regular flow is maintained. Some Common examples of exceptions include ClassNotFoundException, IOException, SQLException, RemoteException, etc. By handling these exceptions, Java enables deve
8 min read
Java Try Catch BlockA try-catch block in Java is a mechanism to handle exceptions. This make sure that the application continues to run even if an error occurs. The code inside the try block is executed, and if any exception occurs, it is then caught by the catch block.Example: Here, we are going to handle the Arithmet
4 min read
Java final, finally and finalizeIn Java, the final, finally, and finalize keywords play an important role in exception handling. The main difference between final, finally, and finalize is listed below:final: The final is the keyword that can be used for immutability and restrictions in variables, methods, and classes.finally: The
4 min read
Chained Exceptions in JavaChained Exceptions in Java allow associating one exception with another, i.e. one exception describes the cause of another exception. For example, consider a situation in which a method throws an ArithmeticException because of an attempt to divide by zero.But the root cause of the error was an I/O f
3 min read
Null Pointer Exception in JavaA NullPointerException in Java is a RuntimeException. It occurs when a program attempts to use an object reference that has the null value. In Java, "null" is a special value that can be assigned to object references to indicate the absence of a value.Reasons for Null Pointer ExceptionA NullPointerE
5 min read
Exception Handling with Method Overriding in JavaIn Java, an exception is an unwanted or unexpected event that occurs during a program's execution, i.e., at runtime, and disrupts the normal flow of the programâs instructions. Exception handling in Java handles runtime errors and helps maintain the program's normal flow by using constructs like try
5 min read
Java Advanced
Java Multithreading TutorialThreads are the backbone of multithreading. We are living in the real world which in itself is caught on the web surrounded by lots of applications. With the advancement in technologies, we cannot achieve the speed required to run them simultaneously unless we introduce the concept of multi-tasking
15+ min read
Synchronization in JavaIn multithreading, synchronization is important to make sure multiple threads safely work on shared resources. Without synchronization, data can become inconsistent or corrupted if multiple threads access and modify shared variables at the same time. In Java, it is a mechanism that ensures that only
10 min read
File Handling in JavaIn Java, with the help of File Class, we can work with files. This File Class is inside the java.io package. The File class can be used to create an object of the class and then specifying the name of the file.Why File Handling is Required?File Handling is an integral part of any programming languag
6 min read
Java Method ReferencesIn Java, a method is a collection of statements that perform some specific task and return the result to the caller. A method reference is the shorthand syntax for a lambda expression that contains just one method call. In general, one does not have to pass arguments to method references.Why Use Met
9 min read
Java 8 Stream TutorialJava 8 introduces Stream, which is a new abstract layer, and some new additional packages in Java 8 called java.util.stream. A Stream is a sequence of components that can be processed sequentially. These packages include classes, interfaces, and enum to allow functional-style operations on the eleme
15+ min read
Java NetworkingWhen computing devices such as laptops, desktops, servers, smartphones, and tablets and an eternally-expanding arrangement of IoT gadgets such as cameras, door locks, doorbells, refrigerators, audio/visual systems, thermostats, and various sensors are sharing information and data with each other is
15+ min read
JDBC TutorialJDBC stands for Java Database Connectivity. JDBC is a Java API or tool used in Java applications to interact with the database. It is a specification from Sun Microsystems that provides APIs for Java applications to communicate with different databases. Interfaces and Classes for JDBC API comes unde
12 min read
Java Memory ManagementJava memory management is the process by which the Java Virtual Machine (JVM) automatically handles the allocation and deallocation of memory. It uses a garbage collector to reclaim memory by removing unused objects, eliminating the need for manual memory managementJVM Memory StructureJVM defines va
4 min read
Garbage Collection in JavaGarbage collection in Java is an automatic memory management process that helps Java programs run efficiently. Java programs compile to bytecode that can be run on a Java Virtual Machine (JVM). When Java programs run on the JVM, objects in the heap are created, which is a portion of memory dedicated
7 min read
Memory Leaks in JavaIn programming, a memory leak happens when a program keeps using memory but does not give it back when it's done. It simply means the program slowly uses more and more memory, which can make things slow and even stop working. Working of Memory Management in JavaJava has automatic garbage collection,
3 min read
Practice Java
Java Interview Questions and AnswersJava is one of the most popular programming languages in the world, known for its versatility, portability, and wide range of applications. Java is the most used language in top companies such as Uber, Airbnb, Google, Netflix, Instagram, Spotify, Amazon, and many more because of its features and per
15+ min read
Java Programs - Java Programming ExamplesIn this article, we will learn and prepare for Interviews using Java Programming Examples. From basic Java programs like the Fibonacci series, Prime numbers, Factorial numbers, and Palindrome numbers to advanced Java programs.Java is one of the most popular programming languages today because of its
8 min read
Java Exercises - Basic to Advanced Java Practice Programs with SolutionsLooking for Java exercises to test your Java skills, then explore our topic-wise Java practice exercises? Here you will get 25 plus practice problems that help to upscale your Java skills. As we know Java is one of the most popular languages because of its robust and secure nature. But, programmers
7 min read
Java Quiz | Level Up Your Java SkillsThe best way to scale up your coding skills is by practicing the exercise. And if you are a Java programmer looking to test your Java skills and knowledge? Then, this Java quiz is designed to challenge your understanding of Java programming concepts and assess your excellence in the language. In thi
1 min read
Top 50 Java Project Ideas For Beginners and Advanced [Update 2025]Java is one of the most popular and versatile programming languages, known for its reliability, security, and platform independence. Developed by James Gosling in 1982, Java is widely used across industries like big data, mobile development, finance, and e-commerce.Building Java projects is an excel
15+ min read