Java - RandomAccessFile writeUTF(String str) method

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Description

The Java RandomAccessFile writeUTF(String str) method writes a string to the file using modified UTF-8 encoding in a machine-independent manner.

Declaration

Following is the declaration for java.io.RandomAccessFile.writeUTF(String str) method.

 public final void writeUTF(String str) 

Parameters

str − a string to be written.

Return Value

This method does not return a value.

Exception

• IOException − If an I/O error occurs.

Example - Usage of RandomAccessFile writeUTF(String str) method

The following example shows the usage of RandomAccessFile writeUTF(String str) method.

RandomAccessFileDemo.java

 package com.tutorialspoint; import java.io.RandomAccessFile; import java.io.IOException; public class RandomAccessFileDemo { public static void main(String[] args) { try { String s = "Hello world"; // create a new RandomAccessFile with filename test RandomAccessFile raf = new RandomAccessFile("test.txt", "rw"); // write a string in the file raf.writeUTF(s); // set the file pointer at 0 position raf.seek(0); // read string System.out.println(raf.readUTF()); // set the file pointer at 0 position raf.seek(0); // write a string at the start raf.writeUTF("This is an example"); // set the file pointer at 0 position raf.seek(0); // read string System.out.println(raf.readUTF()); } catch (Exception ex) { ex.printStackTrace(); } } } 

Output

Assuming we have a text file test.txt in current directory which has the following content. This file will be used as an input for our example program −

 ABCDE 

Let us compile and run the above program, this will produce the following result −

 Hello world This is an example 

Example - Writing and Reading a Single UTF String

The following example shows the usage of RandomAccessFile writeUTF(String str) method.

RandomAccessFileDemo.java

 package com.tutorialspoint; import java.io.RandomAccessFile; import java.io.IOException; public class RandomAccessFileDemo { public static void main(String[] args) { try (RandomAccessFile raf = new RandomAccessFile("utf1.dat", "rw")) { // Write a UTF string raf.writeUTF("Hello, World!"); // Reset file pointer to the beginning raf.seek(0); // Read the UTF string String result = raf.readUTF(); System.out.println("Read string: " + result); } catch (IOException e) { e.printStackTrace(); } } } 

Output

Let us compile and run the above program, this will produce the following result−

 Read string: Hello, World! 

Explanation

• writeUTF("Hello, World!") writes−

  • A 2-byte length prefix

  • Followed by the UTF-8 encoded bytes of the string

• readUTF() reads the length and the encoded string.

Example - Writing and Reading Multiple UTF Strings

The following example shows the usage of RandomAccessFile writeUTF(String str) method.

RandomAccessFileDemo.java

 package com.tutorialspoint; import java.io.RandomAccessFile; import java.io.IOException; public class RandomAccessFileDemo { public static void main(String[] args) { try (RandomAccessFile raf = new RandomAccessFile("utf2.dat", "rw")) { // Write multiple UTF strings raf.writeUTF("Java"); raf.writeUTF("RandomAccessFile"); raf.writeUTF("writeUTF"); // Reset pointer to start of file raf.seek(0); // Read the strings back System.out.println("1st string: " + raf.readUTF()); System.out.println("2nd string: " + raf.readUTF()); System.out.println("3rd string: " + raf.readUTF()); } catch (IOException e) { e.printStackTrace(); } } } 

Output

Let us compile and run the above program, this will produce the following result−

 1st string: Java 2nd string: RandomAccessFile 3rd string: writeUTF 

Explanation

• Each writeUTF() call writes−

  • 2-byte length + UTF-8 bytes of the string.

• You must read strings in the same order as written.

• Total file size = 2 bytes (length) + N bytes (string content) for each string.