Java Program to Append a String in an Existing File

Last Updated : 11 Jul, 2025

In Java, we can append a string in an existing file using FileWriter which has an option to open a file in append mode. Java FileWriter class is used to write character-oriented data to a file. It is a character-oriented class that is used for file handling in Java. Unlike FileOutputStream class, we don't need to convert the string into a byte array because it provides a method to write a string directly.

Note: The buffer size may be specified, or the default size may be used. A Writer sends its output immediately to the underlying character or byte stream.

Let us see constructors used later on adhering towards as usual methods of this class

Constructor: FileWriter(File file, boolean append):

It Constructs a FileWriter object given a File object in append mode. Now let us toggle onto methods of this class which is invoked here and play a crucial role in appending a string in an existing file as follows:

Method 1: write()

This method writes a portion of a String

Syntax:

void write(String s,int off,int len);

Return Type: Void

Parameters:

Input string
int off
String length

Method 2: close()

This method closes the stream after flushing it.

Return Type: Void

Example

Java

// Java Program to Append a String to the // End of a File // Importing input output classes import java.io.*; // Main class class GeeksforGeeks {  // Method 1  // TO append string into a file  public static void appendStrToFile(String fileName,  String str)  {  // Try block to check for exceptions  try {  // Open given file in append mode by creating an  // object of BufferedWriter class  BufferedWriter out = new BufferedWriter(  new FileWriter(fileName, true));  // Writing on output stream  out.write(str);  // Closing the connection  out.close();  }  // Catch block to handle the exceptions  catch (IOException e) {  // Display message when exception occurs  System.out.println("exception occurred" + e);  }  }  // Method 2  // main driver method  public static void main(String[] args) throws Exception  {  // Creating a sample file with some random text  String fileName = "Geek.txt";  // Try block to check for exceptions  try {  // Again operating same operations by passing  // file as  // parameter to read it  BufferedWriter out = new BufferedWriter(  new FileWriter(fileName));  // Writing on. file  out.write("Hello World:\n");  // Closing file connections  out.close();  }  // Catch block to handle exceptions  catch (IOException e) {  // Display message when error occurs  System.out.println("Exception Occurred" + e);  }  // Now appendinggiven str to above  // created file  String str = "This is GeeksforGeeks";  // Calling the above method  appendStrToFile(fileName, str);  // Let us print modified file  try {  BufferedReader in = new BufferedReader(  new FileReader("Geek.txt"));  String mystring;  // TIll there is content in string  // condition holds true  while ((mystring = in.readLine()) != null) {  System.out.println(mystring);  }  }  // Catch block to handle IO exceptions  catch (IOException e) {  System.out.println("Exception Occurred" + e);  }  } }