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.